CORAL SETTLEMENT, SURVIVABILITY, AND - USP Thesesdigilib.library.usp.ac.fj/gsdl/collect/usplibr1/index/assoc/HASH01... · Ronal Lal Date ... To the other co-supervisor of this project

CORAL SETTLEMENT, SURVIVABILITY, AND

DIVERSITY IN A HEAVILY STRESSED URBAN REEF

ENVIRONMENT IN THE FIJI ISLANDS

By

Ronal R. Lal

A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Marine Science

Copyright © 2016 by Ronal R. Lal

School of Marine Studies Faculty of Science, Technology, and Environment

University of the South Pacific

February, 2016

DECLARATION OF ORIGINALITY ____________________________________________________________________

Statement by Author

I, Ronal R. Lal, declare that this thesis is that of my own work, and I affirm that to the

best of my knowledge, it contains no material which has been previously published,

or substantially overlapping with material submitted for the award of any other Degree

at any other institution, except where due acknowledgement is made in the text.

26/02/16

______________ ______________

Ronal Lal Date

S11028170

Statement by Supervisors:

The research in this thesis was performed under my supervision and to my knowledge

is the sole work of Mr Ronal R. Lal.

26/02/16

______________ ______________

Prof. Ciro Rico (principal supervisor) Date

26/02/16

______________ ______________

Dr. Antoine De Ramon N’Yeurt (co-supervisor) Date

i

DEDICATION

____________________________________________________________________

I dedicate this thesis to the Lord Jesus Christ Almighty for His provisions of strength

and guidance, for without Him I would not have been able to accomplish any aspect

of this study.

ii

ACKNOWLEDGEMENTS ____________________________________________________________________

“Fear not; for I am with you: be not dismayed; for I am your God: I will strengthen

you; yea, I will help you; yea, I will uphold you with the right hand of my

righteousness” Isaiah 41:10

“He gives power to the faint; and to them that have no might He increases strength”

Isaiah 40:29

“And He said unto me, My grace is sufficient for thee: for My strength is made perfect

in weakness. Most gladly therefore will I rather glory in my infirmities, that the power

of Christ may rest upon me” 2 Corinthians 12:9

All credit for the work undertaken for this thesis, as well as for the findings of this

study go the Lord Almighty. When facing the prospect of completing back-breaking

field work, and amidst the most challenging conditions that I have ever faced above

and under water in the 29 years of my life, I called upon the Lord for help and He

delivered me through impossible situations each time and with unfailing success.

Thank you for blessing me with the knowledge to write this Father.

This project would not have existed if it were not for its founder the late Mr. Johnson

Seeto, who saw an interesting idea and was willing to accommodate an eager student

to pursue the idea. I will forever be in your debt and I pray that your soul may rest in

eternal peace. To the principal supervisor of this project Professor. Ciro Rico, my

deepest appreciation and thanks for coming aboard for this project, and for your

learned advice and recommendations. Your jovial hospitality and encouragement

throughout the duration of the project was highly appreciated.

My heartfelt gratitude to Dr. Ralph Riley, who was willing to go the extra mile and

spare excessive amounts of time and energy on numerous field trips in order to help

me secure monitoring equipment to the sea floor. Thank you also for helping me with

the experimental design of this project; you are an incredible person of whom I had

the great fortune and pleasure of meeting. To my good friend Mr. Jerome Taoi, words

alone cannot express my sincere gratitude to you for helping me in the establishment

of my primary study site; people of your caliber are very few and far between.

iii

To Mr. Celso Cawich, I cannot express my gratitude to you enough for being my dive

buddy and helping me with each monitoring trip. Your dependability and competence

was pivotal in the success of this project. To Mr. Kelly Brown and Mr. Rahul Tikaram,

thank you for coming along on fieldtrips when I had no dive buddy in order to assist

me in my work; I will most certainly return the favour one day. To Mr. Ed Lovell,

thank you so very much for meeting with me before, during, and after the project on

numerous occasions; and also for your invaluable recommendations on project design,

monitoring techniques, coral species identification and taxonomy, and for providing

me with general motivation and support. Thank you for your kindness and generosity,

I am in your debt always.

To the co-supervisor of this project Professor. John Bythell, a very big thank you to

you for taking the time out for a mere student whilst you were deputy vice-chancellor,

in order to visit my study sites with me for monitoring work, and also to provide

intellectual support in your office. Few leaders in such high offices display the level

of humility and character you possesses. To the other co-supervisor of this project Dr.

Antoine De Ramon N’ Yeurt, I am particularly grateful to you and I extend my sincere

thanks to you, for providing me with guidance and advice for this project, as well as

for going through my chapters and recommending excellent recommendations and

improvements. Your dedication towards helping me improve the quality of my thesis

was really touching. A very big thank you also to Dr. Johanne Poinapen for proving

me with a research assistant position through which I was able to continue my studies,

a very big thank you for this opportunity, and for your kind words and advice. To Mr.

Karuna Reddy of the research office, thank you from the bottom of my heart for

helping me in the organization and analysis of the acquired data; your kind hospitality

and expertise are a true asset to the university and this thesis would not have been

possible without your input. I am always in your debt my good friend.

Thank you as well to Mr. Jone Lima for providing me with all the necessary equipment

in the laboratory and for your kind persona and helpful attitude. To Captain Netani,

Captain Ramesh, and Captain Jim, thank you from the bottom of my heart for your

assistance and help when out at sea. Thank you also to Mr. Fiu Manueli for your help

and assistance with dive gear, and for streamlining the logistics involved in preparing

for boat trips.

iv

ABSTRACT

____________________________________________________________________

A relic inshore reef ecosystem located 400 meters from the Fijian capital City of Suva

and adjacent industrial area was monitored monthly from July 2014 to July 2015 for

coral cover, recruitment rates, sedimentation rates, light intensity, temperature,

salinity, and dissolved oxygen magnitudes (primary inshore site). Five permanent

quadrats, five settlement tile racks, five sediment traps, and two light and temperature

loggers were deployed in this primary site; and in a control site with a similar depth

profile located offshore (control offshore site). Despite a major sewage spill disaster

in Suva Harbour in December 2014, the stressed inshore primary site recorded higher

coral species diversity and similar abundances in comparison to the offshore control

site. A significant decrease in coral cover was observed between July 2014 (27.10%)

and January 2015 (20.33%) in the primary site; however, no significant decrease was

seen in July 2015 (18.47%). Coral spat abundance on artificial substrata (6720 cm 2

per site) was similar for both sites except for Family Poritidae; with relatively similar

total yearly spat abundance between sites: 106 spat inshore, 132 spat offshore. Annual

sedimentation was significantly higher in the inshore primary site (657.14 g.cm 2 ),

compared to the offshore control site (371.52 g.cm 2 ). Particulate Organic Matter

(POM) was also significantly higher in the inshore location (107.51 g.cm 2 ), compared

to the control site (43.37 g.cm 2 ). Mean light intensity was significantly lower for the

primary site (69.81 lum/ft 2 ) compared to the control site (239.26 lum/ft 2 ), with

Photosynthetically Active Radiation (PAR) also lower for the inshore site (800-

1066.66 µmol m 2� s 1� ) compared to the offshore site (3266.66-3600 µmol m 2� s 1� ).

Mean ambient site temperature was consistently similar for the inshore and offshore

sites; 26.87°C and 26.86°C respectively.

v

ABBREVIATIONS AND ACRONYMS ____________________________________________________________________

ADTCR Average Daily Sediment Trap Collection Rate

AFDW Ash Free Dry Weight

ANOVA Analysis of Variance

CC Coral Cover

CDOM Chromophoric Dissolved Organic Matter

COS Control Offshore Site

COTS Crown of Thorns Starfish

CPCe Coral Point Count with excel extensions

CITES Convention on International Trade in Endangered Species

DO 2 Dissolved oxygen (usually specified in mg L 1� )

DH Dynamite Hut

DP Dennis’ Patch

FCON Fish Eye Converter

FLMMA Fiji Locally Managed Marine Areas network

IMEL Industrial and Marine Engineering Limited

MAC Marine Aquarium Council

NOAA National Oceanic and Atmospheric Association

NSS Non-spawning season

PACE-SD Pacific Centre for Environment and Sustainable Development

PAR Photosynthetically Active Radiation

PIS Primary Inshore Site

POM Particulate Organic Matter

PPFD Photosynthetic Photon Flux Density

RSR Recruitment Station Rack

RSYC Royal Suva Yacht Club

vi

SCUBA Self-Contained Underwater Breathing Apparatus

SMS School of Marine Studies

SPSS Software Package for Statistical Analysis

SS Spawning Season

SST Sea Surface Temperature

USP University of the South Pacific

UV Ultra Violet

WWF World Wildlife Fund

vii

UNITS OF MEASUREMENT ____________________________________________________________________

cm centimetre

L litre

Lum/ft² lumens per feet squared

Lux/ m² unit of luminous output equivalent to lumens (lum) or lum/m 2

mgL 1� milligrams per litre

mm millimetre

ppt parts-per-thousand

μm micrometres/micron

µmol m 2� d 1� micromoles per meter per day

µmol m 2� s 1� micromoles per meter per second

viii

TABLE OF CONTENTS ____________________________________________________________________

Dedication i

Acknowledgements ii

Abstract ix

Abbreviations and acronyms v

Units of measurement vii

Table of contents viii

List of table’s xiv

List of figures xvii

Chapter 1 General Introduction

1.1 Coral Reefs: Their value and potential threats to sustainability 1

1.2 Status of Coral Reef’s in the Fiji Islands 1

1.2.1 Subsistence and commercial exploitation of coral reefs in Fiji 2

1.2.2 The Live Rock trade and coral reef sustainability 3

1.3 Coral bleaching events and coral health decline in Fiji’s history 4

1.3.1 Sewage intrusion and its impact on Fijian reef health 5

1.3.2 Turbidity and eutrophication impacts on coral reef health 6

1.3.3 Crown of Thorns starfish, eutrophication, and coral bleaching 8

1.4 Near shore reef resilience, adaptation and tolerance mechanisms 9

1.5 Adaptation of corals to thermal stress in rising sea surface temperatures 11

1.6 lagoon temperature mediation mechanisms and near-shore reefs 13

1.7 Coral recruitment in resistance and resilience after disturbance 15

1.8 Coral reef status, resilience, and recovery in the Fiji Islands 16

1.9 Rationale for study 17

1.10 Purpose and structure of this thesis 18

1.11 Thesis structure 19

1.12 Study areas 21

ix

Chapter 2 Evaluating coral cover and species diversity through monthly

permanent photo-quadrat monitoring

2.1 Introduction 27

2.1.1 Long term monitoring and the permanent photo quadrat method 27

2.1.2 The significance of coral cover 27

2.1.3 Coral cover estimates using photo-quadrats 28

2.1.4 The use of the permanent photo quadrat method 29

2.1.5 Image analysis disadvantages 30

2.2 Research Objectives 31

2.3 Methodology 31

2.3.1 Portable photo quadrat construction 32

2.3.2 Camera tripod stand construction 32

2.3.3 Permanent quadrats establishment 33

2.3.4 Monthly monitoring 33

2.3.5 Image processing and analysis 34

2.4 Results and Discussion 36

2.4.1 Coral cover percentage between sites and monthly trend 36

2.4.2 Coral cover change within sites 37

2.4.3 Coral species diversity between study sites 42

2.4.3.1 Acropora species 43

2.4.3.2 Porites species 44

2.4.3.3 Favites species 45

2.4.3.4 Pocillopora species 46

2.4.3.5 Miscellaneous species 47

2.4.4 Shannon Weaver diversity indices 47

2.5 Conclusion 49

2.5.1 Coral cover abundance: site comparison 49

2.5.2 Coral species diversity and abundance: site comparison 49

x

Chapter 3 Determination of coral recruitment rates in terms of family

abundance and diversity over a seasonal timescale: A site

comparison study

3.1 Introduction 51

3.1.1 Coral recruitment studies and coral health sustainability 51

3.1.2 Coral recruitment assessment methods 51

3.1.2.1 Artificial substrate used in coral recruitment studies 52

3.1.3 Coral recruitment and reef resilience after disturbance 52

3.1.4 Coral recruitment studies in the Fiji islands and reef resilience 53


3.3 Methodology 56

3.3.1 Coral spawning periods in the Fiji Islands 56

3.3.2 Seasonality and coral settlement 57

3.3.3 Settlement tile preparation 57

3.3.4 Recruitment Station Rack (RSR) 58

3.3.5 Study site Recruitment Station Rack field deployment 58

3.3.6 Study site field data collection 60

3.3.6.1 Coral Family “abundance” study 60

3.3.6.2 Coral Family “diversity” study 60

3.3.6.3 Settlement tile retrieval process 60

3.3.7 Laboratory analysis 61

3.3.7.1 Settlement tile laboratory conditioning and preparation 61

3.3.7.2 Dissecting Microscope calibration 62

3.3.7.3 Coral spat searching and identification 62

3.3.7.4 Settlement tile surface area and total coral spat density 63

3.3.7.5 Coral spat characterization 63

3.4 Results and Discussion 68

3.4.1 Coral spat abundance: two month collection intervals 68

3.4.1.1 Coral spat density and coral spawning 71

3.4.1.2 Coral spat abundance in wet and dry seasons 72

3.4.1.3 Zero coral spat count prospective cohort study 73

3.4.2 Coral spat diversity: six month collection intervals 74

3.4.2.1 Coral spat abundance in wet and dry seasons 77

xi

3.4.2.2 Zero coral spat count prospective cohort study 79

3.5 Conclusion 80

3.5.1 Recruitment between sites 80

3.5.2 Coral spat abundance between sites (Six-month study) 80

3.5.3 Coral spat abundance between sites (Two-month study) 81

3.5.3.1 Coral spat and spawning seasons (Two-month study) 81

3.5.4 Relative risk estimate for coral spat presence between sites 81

Chapter 4 Determination of long-term sedimentation rates in view of

identifying the magnitude of this stressor influence on coral health

4.1 Introduction 83

4.1.1 The use of sediment traps in coral reef health monitoring 83

4.1.2 Coral reef sedimentation in Fiji: Past evaluations 83

4.1.3 Impairment of coral fertility through high sedimentation 84

4.1.4 Coral persistence in high sedimentation environments 85

4.1.5 Coral physiological response to high sedimentation 86

4.1.6 Coral compensatory response in light deprived environments 86


4.3 Methodology 88

4.3.1 Sediment trap construction 88

4.3.2 Study site field deployment 89

4.3.3 Study site field data collection 90

4.3.4 Monthly consecutive deployment 91

4.3.5 Laboratory analysis 91

4.4 Results 93

4.4.1 Annual sediment dry weight between sites 93

4.4.1.1 Dry-weight and seasonality 96

4.4.2 Annual Particulate Organic Matter load between sites 96

4.4.2.1 POM and seasonality 99

4.4.2.2 POM percentage in sediment dry-weight between sites 100

4.4.3 Average Daily Sediment Trap Collection Rate (ADTCR) 103

4.5 Conclusion 106

xii

4.5.1 Sediment dry-weight between study sites 106

4.5.2 Sediment dry-weight and seasonality 107

4.5.3 Annual Particulate Organic Matter between sites 107

4.5.4 POM and seasonality 107

4.5.5 POM percentage in sediment dry weight between sites 108

4.5.6 Average Daily Sediment Trap Collection Rate between sites 108

Chapter 5 Long-term monitoring of in-situ temperature, light intensity,

salinity, and dissolved oxygen values in terms of stressor magnitude

identification

5.1 Introduction 109

5.1.1 Environmental conditions in coral resistance 109

5.1.2 Resilience and coral reef sustainability 110

5.1.3 Algal symbionts in acquired thermal tolerance 110

5.1.4 Photosynthetic Photon Flux Density (PPFD) 111

5.1.5 Zooxanthellae and light intensity tolerance 111

5.1.6 Eutrophication and Dissolved Oxygen 113

5.1.7 Salinity and its impact on coral fertility 115

5.1.8 Sea Surface Temperature, solar energy and coral health 115


5.3 Methodology 117

5.3.1 Data loggers and associated equipment 117

5.3.2 Data logger calibration 117

5.3.2.1 Light Intensity: method for standardised measure 117

5.3.2.2 Temperature: method for standardised 118

5.3.3 Study site field deployment 118

5.3.4 Data logger retrieval, data readout, and data tabulation 120

5.3.5 YSI-85 Salinity, and Dissolved Oxygen measurements 121

5.4 Results 121

5.4.1 Daily Light Intensity for coral photosynthesis in study sites 121

5.4.2 Daily Photosynthetic Photon Flux Density (PPFD) in study sites 125

5.4.3 Daily water temperature in study sites 129

5.4.3.1 Daily maximum site temperature 132

xiii

5.4.4 Monthly site salinity values between study sites 134

5.4.5 Monthly site dissolved oxygen values between study sites 136

5.5 Conclusion 137

5.5.1 Light intensity influence in the (PIS) 137

5.5.2 Mean site water temperature between sites 138

5.5.3 Mean monthly Salinity and Dissolved Oxygen in study sites 138

5.5.4 Recommendations for Suva Harbour coral assemblages 139

Chapter 6 General conclusion and recommendations

6.1 Review of objectives 141

6.1.1 Coral cover and species diversity in the (PIS) 141

6.1.2 Coral spat Family diversity and abundance 142

6.1.3 Environmental parameter magnitudes in the (PIS) 144

6.1.4 Recommendations for further study 146

References 148

Appendices

1.0 View of Suva City and Walu Bay Industrial area from within the (PIS) 154

1.1 Various coral species present in the (PIS) 155

1.2 Reduction in coral cover from 33.65 % to 6.67% in Quadrat 4 through 160

dredging works carried out in immediate (PIS), and photograph of

dredging equipment on barge

1.3 Recruitment Station Rack in the (PIS) showing sediment film 161

adhering onto settlement tile surfaces

xiv

LIST OF TABLES ____________________________________________________________________

Chapter 1

Table 1.0 GPS coordinates for individual permanent quadrats

23

Table 1.1 GPS coordinates for individual permanent quadrats

26

Chapter 2

Table 2.0 Major categories and respective site abundance

36

Table 2.1 Friedman’s test results: PIS

37

Table 2.2 Wilcoxon’s post-hoc test between observation months

38

Table 2.3 Friedman’s test results: COS

39

Table 2.4 Coral species percentage of monthly coral cover

42

Table 2.5 Acropora species Mann-Whitney U test values between sites

44

Table 2.6 Porites species Mann-Whitney U test values between sites

45

Table 2.7 Favites species Mann-Whitney U test values between sites

46

Table 2.8 Pocillopora species Mann-Whitney U test values between sites

46

Table 2.9 Miscellaneous species Mann-Whitney U test values between sites

47

Table 2.10 Coral species diversity between sites

48

Chapter 3

Table 3.0 Predicted mass spawning events in the Fiji Islands

57

Table 3.1 Coral spat identification key for differentiation at Family level using skeletal structural features

63

Table 3.2

Total coral spat from two month collection intervals

68

Table 3.3 Coral spat Family two-month interval abundance 70

xv

Table 3.4 Mann-Whitney U test for coral spat abundance between

sites

71

Table 3.5 Sum of coral spat found in differing spawning seasons

72

Table 3.6 Sum of coral spat found in wet and dry seasons

72

Table 3.7 Pearson’s Chi Squared test results for coral spat

abundance in alternate seasons

73

Table 3.8 Prospective cohort study in terms of zero coral spat count risk estimates

74

Table 3.9 Total coral spat from six month collection intervals

74

Table 3.10 Coral spat Family six-month interval abundance

76

Table 3.11 Mann-Whitney U test for coral spat abundance between sites

77


78

Table 3.13 Pearson’s Chi Squared test results for coral spat

abundance in alternate seasons

79

Table 3.14 Prospective cohort study in terms of zero coral spat count risk estimate

80

Chapter 4

Table 4.0 Annual mean and sum of sediment dry weight between study sites

94

Table 4.1 Mann-Whitney U test results for sediment dry weight between sites

96

Table 4.2 Mean sediment dry weight in alternate seasons between sites

96

Table 4.3 Annual mean and sum of sediment POM between study sites

97

Table 4.4 Mann-Whitney U test results for sediment POM between sites

99

Table 4.5 Mean sediment POM in alternate seasons between sites

100

xvi

Table 4.6 Mean and sum of POM percentage in dry-weight between sites

101

Table 4.7 Mann-Whitney U test results for POM content in

sediment dry weight between sites

103

Table 4.8 Mean and sum of ADTCR in terms of sediment dry-

weight between sites

104

Table 4.9 Mann-Whitney U test results for ADTCR in terms of

sediment dry weight between sites

106

Chapter 5

Table 5.0 Data logger depth values within each study site

122

Table 5.1 One-Way ANOVA test results and annual mean light intensity values recorded between sites at similar depth profile

124

Table 5.2 Tukey HSD post-hoc test results

124

Table 5.3 One-Way ANOVA test results and annual mean PPFD values recorded between sites at similar depth profiles

128

Table 5.4 Tukey HSD post-hoc test results 128

Table 5.5 Annual mean temperature between depth profiles in

study sites

129

Table 5.6 Daily mean and maximum temperatures (February 2015-March 2015)

130

Table 5.7 Annual mean maximum temperature between depth profiles in study sites

132

Table 5.8 Monthly mean salinity values between study sites

135

Table 5.9 Monthly mean dissolved oxygen values between study sites

136

xvii

LIST OF FIGURES ____________________________________________________________________

Chapter 1

Figure 1.0 Average coral cover at two depth categories from core survey sites on Fijian Reefs, depicting a clear recovery trend from the 2000 bleaching event and Crown-of-Thorns starfish.

16

Figure 1.1 Photograph of the “Dynamite Hut” structure taken on

15/07/14

21

Figure 1.2 General location of the ‘Dynamite Hut’ structure outlined

in red insert and in relation to Suva Harbour

22

Figure 1.3 Copious amounts of possible diesel or petroleum oil observed on water surface in immediate study area

23

Figure 1.4 General location of Dennis’ Patch reef outlined in red

insert and in relation to Suva Harbour, and geo-referenced permanent quadrat locations in aerial photograph

25

Chapter 2

Figure 2.0 Assembled 2×2 meter portable quadrat

32

Figure 2.1 Lateral view and top view of the tripod camera stand

33

Figure 2.2 A CPCe processed photograph from the primary study site: Permanent Quadrat 1 (sub-quadrat 16), showing 20 randomly generated points

35

Figure 2.3 Bar graph displaying major category abundance between study sites for months 1, 7 and 12

36

Figure 2.4 Coral cover comparison in study sites

41

Figure 2.5 Acropora species abundance between sites and over a twelve month duration

43

Figure 2.6 Porites species abundance between sites and over a twelve month duration

44

Figure 2.7 Favites species abundance between sites and over a twelve month duration

45

xviii

Figure 2.8 Pocillopora species abundance between sites and over a twelve month duration

46

Figure 2.9 Miscellaneous species abundance between sites and over a twelve month duration

47

Chapter 3

Figure 3.0 Frontal view of an assembled (RSR), and an (RSR) being deployed in the Primary study site by the researcher

59

Figure 3.1 Lateral view of a Recruitment Station Rack

59

Figure 3.2 Two of the three specially fabricated settlement tile collection trays

61

Figure 3.3 Photomicrograph of a Family Mussidae coral spat with visible skeletal structural features

64

Figure 3.4 Photomicrograph of a Family Poritidae coral spat with distinguishing septal teeth clearly visible

64

Figure 3.5 Photomicrograph of a Family Acroporidae spat with prominent septa visible, along with the distinctive lack of a columella

65

Figure 3.6 Photomicrograph of a Family Pocilloporidae spat with prominent columella clearly visible

66

Figure 3.7 Coral spat classified under the “Unidentifiable” category

67

Figure 3.8 Coral spat family abundance: two month collection interval

69

Figure 3.9 Coral spat family abundance: six month collection intervals

75

Chapter 4

Figure 4.0 Recommended sediment trap design, and constructed sediment trap

89

Figure 4.1 Sediment trap shown in situ at primary study site

90

Figure 4.2 Sediment traps prepared for retrieval, and retrieved traps ready for weight and composition analysis

90

Figure 4.3 Securing of fresh PVC traps

91

xix

Figure 4.4 Mean sedimentation between study sites

95

Figure 4.5 Mean POM between study sites

98

Figure 4.6 Mean POM percentage in sediment dry-weight between study sites

102

Figure 4.7 Mean ADTCR in terms of sediment dry-weight between study sites

105

Chapter 5

Figure 5.0 Maximal light intensity requirement of Pocillopora damicornis coral

112

Figure 5.1 Maximal light intensity requirement of Porites lobata coral

113

Figure 5.2 A HOBO data logger freshly deployed in the primary study site

119

Figure 5.3 Daily shallow zone comparative light intensity values between sites

122

Figure 5.4 Daily deep zone comparative light intensity values between sites

123

Figure 5.5 Daily shallow zone comparative PPFD values between sites

126

Figure 5.6 Daily deep zone comparative PPFD values between sites 126

Figure 5.7 Daily shallow zone comparative temperature values

between sites

131

Figure 5.8 Daily deep zone comparative temperature values between sites

131

Figure 5.9 Daily shallow zone comparative maximum temperature values

133

Figure 5.10 Daily deep zone comparative maximum temperature values

134

Figure 5.11 Monthly comparative salinity values between study sites

136

Figure 5.12 Monthly comparative dissolved oxygen values between study sites

137

Ronal Lal GENERAL INTRODUCTION

1

CHAPTER ONE

GENERAL INTRODUCTION

1.1 Coral Reefs: Their value and potential threats to sustainability

Coral reefs are exceptionally diverse marine ecosystems which serve as fundamental

habitats for a vast amount of fish and invertebrate species. They are instrumental to

human survival and to the economy of tropical countries in terms of coastal buffer

protection, subsistence seafood provision, and as natural infrastructure for eco-

tourism. Although it is known that coral reefs constitute less than 0.1% of the world’s

ocean surface (Brodie et al., 2005; Couce et al., 2012), they hold significant value in

terms of plant and animal biodiversity and account for up to 25% of marine species

(Rocha & Bowen, 2008; Rocha et al., 2005); and in addition to sustaining myriad

commercially-important marine species. In this regard it has been estimated that

services provided by coral reefs in terms of global eco-tourism and coastal buffer

protection amount to USD$29.8 billion annually (Cesar et al., 2003; Costanza et al.,

1997). The sustainability of coral reefs are threatened globally by anthropogenic

factors including pollution, sedimentation, freshwater influxes from waste water

runoff resulting in toxicity, salinity variation, variation in sea surface temperature

(SST) from global warming, and variation in light intensity through suspended

sediment in the water column. These stressors can have lethal or sub-lethal

consequences for corals in terms of reduced growth, reduced reproductive capacity,

increased respiration, and coral bleaching which is the expulsion of symbiotic

photosynthetic algae known as zooxanthellae from the coral polyp host, and which

may eventually lead to a bare coral skeleton and a dead coral reef.

1.2 Status of Coral Reef’s in the Fiji Islands

The Fiji Islands are known to host one of the largest coral reef systems in the South

West Pacific, numbering more than 1000 coral reefs and spanning more than 10 020

km 2 (Quinn & Kojis, 2008; Wilkinson, 2008). In addition to this, Fiji is also known

to host approximately 35 percent of all coral reef area in the entire South West Pacific

(Jupiter et al., 2012), with the variants of these reefs including fringing, barrier,

platform, oceanic, ribbon and drowned reefs (Chin et al., 2011). There is also a wealth


2

of biodiversity with 219 species of hard coral, 2031 species of coral reef fishes, 478

species of marine molluscs, and 422 taxa of marine algae (Chin et al., 2011). A report

by the Global Coral Reef Monitoring Network (GCRMN) states that Fijian coral reefs

have been constantly threatened since 2000 through overexploitation for commercial

and subsistence use, rising sea surface temperatures, pollution and mining , and refuse

disposal (Wilkinson, 2002). It is reported that over half the population of Fiji is rural,

with many of these communities primarily relying on commercial or subsistence

fishing for their livelihood, with over 75% of dietary protein being sourced from the

ocean for their nutrition (Morris, 2009; Sykes & Lovell, 2007). The Status of Coral

Reefs of the Pacific: 2011 handbook assigns an “evidence of change - medium

Confidence” status to Fiji reefs in terms of use of reef resources, stating: “There is

some information available that suggests that human use of Fiji’s coral reefs has

depleted some resources, and may threaten the long-term sustainability of these

extractive activities. The activities of most concern include subsistence and

commercial fishing, and potentially collecting for the marine aquarium trade” (Chin et

al., 2011).

1.2.1 Subsistence and commercial exploitation of coral reefs in Fiji

Through the findings of a socioeconomic survey conducted by the Institute of Applied

Sciences at the University of the South Pacific at 29 locations, it was learned that

marine resources comprised of a significant portion (FJD $636) of the average village

monthly income. In addition to this, a majority of the households also harvest marine

resources for domestic consumption, with the common methods of harvest involving

men using nets and spears to fish ; whilst women use nets, fishing lines, and also glean

the reef (Chin et al., 2011). Data acquired through the distribution of a log book and

coordinated by the Institute of Applied Sciences and FLMMA (Fiji Locally Managed

Marine Areas network), revealed that near shore fisheries in Fiji are critically

threatened as a direct result of commercialization of the aforesaid fisheries with up to

70% of the catch of fish and invertebrates being sold. The harvesting of juvenile fish

also compounds the situation as out of the two most common fish species targeted,

74% and 88% of individual fishes taken were below the size of maturity, thereby not

allowing for spawning before removal from the reef (Comley, 2008). With the advent

of increasing populations as well as developing technology, there is now greater

pressure on the fish stocks of the Fiji Islands.


3

1.2.2 The Live Rock trade and coral reef sustainability

The Fiji Islands have a lucrative aquarium products export industry which consists of

the exportation of ornamental fish, invertebrates, corals, and “live rock” which is

porous coral rubble material originating from dead coral. Live rock is typically covered

with coralline algae which is usually pink or purple in colour and is used in aquariums

to form a natural reef habitat for tropical fish, corals, and invertebrates. The coralline

algae on the live rock are considered highly beneficial as it helps keep aquarium water

clean (Morris, 2009; Owen, 2003; Sykes & Lovell, 2007). This particular trade is vital

to the livelihoods of some Fijian villages as the only viable source of income, and it

was reported that in 2000 over 800,000 kg of live rock was harvested and exported

from the Fiji Islands alone (Owen, 2003). This number was increased to 1.3 million

kilograms in 2004 (Baker, 2015). The actual process of live rock extraction involves

that of villagers selecting rock substrate covered in coralline algae light to dark pink

in colour, using iron rods to break and extract pieces of rock, loading the selected

pieces onto bamboo rafts (indigenously termed bilibili), transferring the harvest onto

the beach by way of horses, and then placing it into boxes to be transported to a

processing facility (Owen, 2003).

In July 2005 the CITES database with the Fiji Fisheries Department, reports that

169,143 ornamental fish along with 31,900 invertebrates were removed from Fijian

ecosystems and exported in order to supply the overseas aquarium trade. The Fiji

Fisheries Department also reports that in 2001 311, 097 aquarium fish were removed

and exported from the Fiji Islands (Baker, 2015). The sustainability of near shore coral

reefs in areas targeted for the live rock trade are directly threatened due to the removal

and destruction of marine habitats for fish and invertebrate species. It has been

recommended that the harvesting of stony corals and “live rock” in the South Pacific

region should be undertaken in a controlled manner until further evaluation of the

impact on ecological habitats is made available (Wright & Hill, 1993).

It has also been argued by Wood (1985) that the disruption and removal of stony corals

from their habitat would hold severe ecological repercussions. In this respect, the

harvesting and collection of corals and “live rock” has been banned in Florida and

Hawaii. However, it has also been suggested by Wright and Hill (1993), that the

harvesting of marine organisms for the aquaculture trade not be prohibited entirely due


4

to the considerable demand for it, and that with moderated harvesting protocols, the

sustainability of the coral reef ecosystem would be thus ensured. Sprung (1991), also

supports this notion and advocates for the continued harvest of “live rock” in Florida

on the basis of the commercial benefits of aquaculture.

The integrity of the reef structure itself is also compromised through the removal and

harvesting of the reef crest, which can induce underwater erosion and bring about

further habitat displacement and destruction. In addition to this there is also an

unnecessary destruction and extraction of habitats as not all harvested live rock is

selected, but discarded along beaches as reject pieces. Efforts employed by the Fiji

Government to regulate the live rock trade in 2001 included a call for an environmental

assessment to inform policy on the trade. With respect to this the World Wildlife Fund

(WWF) in partnership with the Marine Aquarium Council (MAC) initiated a project

and devised two objectives: to develop community based processes for wise coral

harvesting and management, and to help the government structure sound policies and

legislation that will support a sustainable aquarium trade (Owen, 2003).

Information presented in Lal and Cerelala (2005) shows the live rock trade in Fiji to

be still quite active, whereby, in the capital city of Suva the extraction of Porites

boulder coral used in the construction of septic tanks still continues unabated. The

researchers also emphasise that the worldwide harvest of “live rock” has been shown

to bring about deleterious effects to the ecological condition of coral reefs, as well

adverse impacts on the coastal fisheries stocks sustaining many rural communities. In

terms of the mariculture of “live rock” as an alternative to wild harvest in the Fiji

Islands, it was mentioned that due to the highly profitable and financially viable

venture of wild coral and “live rock” harvest conducted by qoliqoli (traditional fishing

ground custodians) members and exporters, a lack of incentive thereby exists in

engaging in the culture of these products due to lower profitability yields.

1.3 Coral bleaching events and coral health decline in Fiji’s history Coral health monitoring in the Fiji Islands between 1997 and 2007 revealed substantial

variability in terms of coral cover, signifying the diversity of Fiji’s reefs between

different areas, and changes over time attributed to episodic disturbances (Chin et al.,

2011). A major impairment to coral diversity in Fiji was the mass coral bleaching event


5

of 2000 due to warm water temperatures which caused a mass mortality of between

40% and 80% of hard coral colonies at reef sites (Morris, 2009). There were also coral

bleaching events in 2002 and 2006; however, these events were deemed more localised

and less severe. An analysis of water temperatures and coral cover recorded during

this period revealed a bleaching ‘threshold’ for Fiji corals whereby it was found that

exposure of corals to temperatures greater than 29 C for more than 60 consecutive

days leads to coral bleaching (Morris, 2009; Sykes & Lovell, 2007). Reduction in

coral cover during this period was also attributed to regional Crown-of-Thorns Starfish

(COTS) outbreaks, however, coral cover was restored to pre-bleaching levels by 2005

(Sykes & Lovell, 2007).

The National Oceanic and Atmospheric Administration (NOAA) bleaching alerts for

the Fiji Islands, report the hottest temperatures on record for the last three years. For

March and April, 2015 the NOAA predicted alert levels 1 and 2; with alert level 2

pertaining to widespread coral mortality. Future trends point to warmer temperatures,

and uncertain prospects for corals in the Pacific region, whereby for a period of 9-12

weeks commencing in November 2015, the outlook is predicted to be alert level 1

(NOAA, 2015).

1.3.1 Sewage intrusion and its impact on Fijian reef health

The process of eutrophication adversely impacts the health and development of coral

reefs. Eutrophication is defined as “The response of an aquatic ecosystem to the

addition of artificial or natural nutrients, mainly phosphates, fertilizers, sewage, or

detergents” (Schindler & Vallentyne, 2004). The discharge of raw untreated sewage

into marine ecosystems brings about the process of eutrophication. In a recent

occurrence, on the 6th of December 2014 at Suva Harbour, Fiji, data released by the

Water Authority of Fiji estimated that more than 200 litres per second of untreated

sewage was being discharged into the Laucala Basin and Suva foreshore throughout

16 days as result of a broken sewerage trunk line pipe. The spill remained uncontained

until December 24, whereupon a temporary bypass pipe was installed.

This environmental disaster holds severe repercussions for coral reef assemblages in

the Harbour in terms of macro algal proliferation due to nutrient enrichment, low light


6

availability through increased turbidity, along with smothering and change in surface

properties via increased sedimentation. The resilience and persistence of the existing

coral reef assemblages in Suva Harbour and their overall response to this major

anthropogenic stressor event has to be investigated; as it is documented that

eutrophication brings about reduced coral recruitment and diversity through

sedimentation, reduced photosynthetic activity and metabolic processes of corals

through turbidity, a prevalence of coral degrading Crown-of-Thorns starfish

(Acanthaster planci), and changes in trophic structure through the nutrient enrichment

of the water body (Fabricius, 2011).

The sustainability of coral reef assemblages in the Laucala Basin and Suva foreshore

are constantly threatened by watershed pollution (sedimentation, nutrients and other

land-based pollutants). An Integrated Threat Analysis carried out by the University of

the South Pacific for 15 regions around Fiji revealed that reef area in Viti Levu, Suva

experiences very high pollution, high sediment damage, high over-fishing, medium

destructive fishing, and medium coastal development (Morris, 2009). An Investigation

into coral recovery or resilience during post-sewage discharge conditions, and

persistence in polluted conditions on a long term basis is imperative in order to obtain

valuable information on coral larval recruitment during altered sedimentation regimes,

light availability in turbid conditions, local temperature conditions, photographic

monitoring in order to ascertain mortality and recovery phases, and sedimentation

rates. Most field studies investigating sewage-pollution effects on coral-reef

ecosystems have been short term and limited in scope (Pastorak & Bilyard, 1985),

however one credible study involving a sewage stressed ecosystem was conducted in

Kaneohe Bay, Oahu, Hawaii (Law & Redalje, 1982). This area experienced a decrease

in coral cover, taxonomic richness, water clarity, and decreased calcification rate as a

result of sewage effluent. Conversely, phytoplankton biomass and total primary

productivity was increased, as was evident in the increased biomass of the bubble alga

Dictyosphaeria cavemosa which caused the mortality of corals by smothering reef

organisms through the formation of thick contiguous mats.

1.3.2 Turbidity and eutrophication impacts on coral reef health

Turbidity is another major adverse mechanism arising from eutrophication which

serves to limit light availability for coral photosynthetic processes. Coastal reefs are


7

known to flourish at relatively high levels of turbidity; however, they tend to be

restricted to the upper 4-10 meters because of reduced coral photosynthesis and growth

at greater depth (Fabricius, 2011). It is also known that altered sedimentation regimes

are a direct consequence of eutrophication, as particulate matter eventually settles onto

the seafloor and also on benthic organisms. The smallest sediment grain fractions (clay

and silt particles) remain in suspension for extended periods of time and undergo

numerous cycles of deposition and re-suspension. It has been found that these small

particles carry more nutrients and pesticides, absorb more light, and cause greater

stress and damage to corals (Gibbs & Matthew, 1971; Moody et al., 1987; Weber et

al., 2006).

Research conducted in Thailand evaluating the impacts of storm water runoff and

sewage discharge in coastal waterways and reef communities discovered that these

pollutants bring about a decrease in dissolved oxygen levels in coastal water by

promoting microbial populations. It was found that the increased presence of nutrients

through wastewater influxes facilitated algal blooms, causing significant changes in

the percentage cover of corals and the depletion of critical fish species in the reef

communities (David et al., 2006). Fabricius (2011) also states that most studies have

shown that high levels of dissolved inorganic nitrogen and phosphorus arising from

eutrophication can cause significant physiological changes in corals but do not kill or

greatly harm individual coral colonies. The persistent presence of corals in these

unfavourable conditions is explained by Dubinsky and Stambler (2011), where the

authors state that tolerance which occurs in polluted populations may be attributed to

the fact that detoxification mechanisms present within coral are sufficient to deal with

elevated exposures to the pollutants, or due to dispersal and mixing between

contaminated regions and that of reference populations. The study also relates that

corals acclimate to their polluted surroundings through a compensatory physiological

response, and that this pre-exposure to chemicals can help to induce and enhance the

detoxification process; dramatically supplementing their resilience and persistence in

stressful environments. Rosenburg and Falkovitz (2011) also state that there are at least

two documented cases where corals became resistant to specific pathogens, Oculina

patagonica to Vibrio shiloi (Reshef et al., 2006), and Caribbean corals to the causative

agent of WPD Aurantimonas coralicidia (Richardson & Aronson, 2002 ).


8

1.3.3 Crown of Thorns starfish, eutrophication, and coral bleaching

Crown-of-Thorns starfish (Acanthaster planci) is known as a corallivore and is a major

cause of coral bleaching and mortality through its consumption of coral tissue. COTS

have also been the most common cause of coral mortality throughout many tropical

Indo-Pacific regions in the last five decades (Fabricius, 2011). They are often reported

in populations of tens to several hundred thousand and have brought about extensive

coral mortality e.g. The Great Barrier Reef, Australia in the 1960’s and 1980’s where

significant outbreaks of A. planci brought about reduced coral cover on some reefs by

more than 50% (Houk et al., 2007).

In the Fiji Islands coral reefs have been reported to be affected by COTS which

occasionally reach high population densities and consume large amounts of live coral

(Chin et al., 2011). There is anecdotal evidence from village elders over the age of 65

in the Fiji Islands, whereby it is stated that an increased frequency of COTS outbreaks

is more common in recent years, in comparison to earlier times (Zann et al., 1990).

Village elders also report extensive COTS outbreak events during the 1920’s and

1930’s, with smaller outbreak events during the 1940’s (Sulu, 2007). In 2002 and 2007

a marginal increase in COTS density was seen, followed by localized outbreaks

recorded in 2005-2006 (Sykes & Lovell, 2007). Control measures for populations of

COTS in Fiji include a COTS control program conducted in the Mamanuca Islands at

dive sites, and which reported a decreasing trend in COTS populations; purported to

be the result of successive COTS control procedures (Chin et al., 2011).

The proliferation of A. planci could be a direct consequence of eutrophication (Brodie

et al., 2005). It is reported through laboratory experiments that the survivorship of

pelagic larvae of COTS is limited to food availability; with steep increases in

survivorship observed in conditions where an increase in the availability of suitable

food at environmentally relevant concentrations was present (Brodie et al., 2005).

Through the process of eutrophication increased nutrient availability can increase the

abundance of large phytoplankton cells, and it has been observed that a strong temporal

and spatial relationship exists between heavy flooding from high continental islands

and outbreaks of COTS (Birkeland, 1997; Fabricius, 2011). This finding is supported

by studies substantiating evidence linking outbreaks of COTS to that of high nutrient


9

levels, and furthermore stating that the abstraction of COTS predators from the

ecosystem will also serve to exacerbate outbreaks (Houk et al., 2007).

The notion that A. planci outbreaks occur in regions with high phytoplankton

concentrations could become a very realistic occurrence in the study sites included in

this investigation; as these study areas are located in close proximity to the general

sewage discharge area in the Laucala basin. Through discussions with Fiji marine

biologist Mr. Ed Lovell, who regularly partakes in surfing activities in Suva Harbour,

he stated that he had observed a “brownish tinge and certain characteristic odour”

associated with the water near to the Suva barrier reef which he attributed to the

significantly heightened presence of phytoplankton; a condition which he had not

encountered prior to the sewage intrusion event (personal communication, January 27,

2015). In addition to this, outbreaks of COTS may also be observed in areas located

further afar from the region of contamination. It is reported that after primary A. planci

outbreaks have formed in locations with high phytoplankton concentrations, many of

their abundant larvae can be transported by currents to isolated and remote areas away

from the initial area of eutrophication (Fabricius, 2011).

1.4 Near shore reef resilience, adaptation and tolerance mechanisms

A study determining bleaching tolerance limits for near-shore corals and their controls,

found that a significant decrease in Gross Primary Production Rates in comparison

with no differences observed for off-shore corals, was revealed throughout the heat

treatment trial (Faxneld et al., 2011). In an earlier study Faxneld et al. (2010) found

that exposing corals to a combination of stressors i.e. high temperature, high nitrate,

and low salinity results in mortality after 24 hours; however, employing the same

stressors but with low temperature does not affect coral metabolism or survival. The

authors attributed this occurrence to a supposition that near-shore corals were probably

pre-exposed to specific stresses such as sedimentation, and land-based pollution; and

as such they would have an impaired and decreased tolerance to that of elevated water

temperatures. In this regard, it was elucidated that these near-shore corals were

probably at the limit of their physiological tolerance when sampled; and were therefore

predisposed to exhibit increased sensitivity to elevated variables i.e. sea surface

temperature (Faxneld et al., 2011). Contrastingly, off-shore corals would not have


10

been subjected to these pre-stressors; and would thereby exhibit significantly higher

tolerance limits.

There is contradiction within the above finding as Faxneld et al. (2011) then explains

that acclimatory ability may change between certain coral species; as it was found that

the species Porites lutea from a near-shore reef area was physiologically tolerant to

elevated temperatures no less than that of the tolerant off shore coral species. Similarly,

an inshore coral reef study site in the Great Barrier Reef which experienced high

sedimentation levels as well as coral bleaching, revealed that a certain coral species

(Acropora sp.) had similar growth rates when compared to the same species at an

offshore reef, and at the same depth (Browne, 2012). In reference to the variation in

bleaching response between that of near-shore reefs and off-shore reefs; with shallow

near-shore reefs purportedly experiencing more severe bleaching events as compared

to off-shore reefs, there is further evidence from similar studies which refute studies

claiming that near-shore reefs are more susceptible to more severe bleaching events.

This has been reportedly attributed to extrinsic environmental factors as well as

physiological intrinsic factors.

Palumbi (2014) carried out transplantation experiments of corals from a shallow hot

location to a shallow cool location, and vice versa in American Samoa. The study

showed that corals from the cool location which were transplanted into the hot location

acquired adaptive heat-tolerance; despite these corals having only half of the heat-

tolerant properties of the hot location corals before the transplantation experiment. It

was reported that these corals acquired immediate heat-tolerance attributes which

should only have been possible if there was a presence of sufficient standing genetic

variation that allowed these corals to quickly adapt to a warmer environment. This

work presents credible findings in terms of the adaptive responses of corals in

changing climatic conditions, as the water temperatures in some shallow American

Samoan reefs can reach up to 35° Celsius; a value high enough to cause coral mortality.

Specific extrinsic environmental factors which promote reef resistance comprise of

temperature systems which have become particular to that local region as well as

incoming solar radiation which brings about a rise in local Sea Surface Temperature

(SST); with a compensation of this mentioned temperature rise brought about by water


11

flushing rates typical to most near shore environmental regions. Moreover, the factor

of shading associated with near shore areas through increased cloud cover also affects

Sea Surface Temperature by limiting the amount of incoming solar radiation entering

the near shore area (Oxenford et al., 2008). Certain intrinsic physiological factors

which also play a part in aiding near-shore reef resistance includes the presence of

health indicators for corals, the type and nature of the coral host, as well as the

genotype of the symbiotic zooxanthellae algae. The genotype of the coral polyp also

plays an important role in the adaptation of the coral to stressors. Kenkel et al. (2011)

assessed the expression of 13 potential genes during excessive heat and light

conditions in Porites astreoides, and observed notably strong differences in gene

expression, and also found rapid return to baseline gene expression levels during a

recovery phase following the environmental stress.

1.5 Adaptation of corals to thermal stress in rising sea surface temperatures

The adaptive response of corals to rising sea surface temperatures involves a process

whereby standing genetic variation is subjected to the forces of natural selection,

whereby, the frequency of allelic variants for the phenotypic traits that positively

affect fitness increase over time, while those that reduce it may disappear completely

from the population (Cossins & Bowler, 1987; Willmer et al., 2004). Clearly reef

forming corals have adapted over time to a wide range of temperatures within tropical

and subtropical latitudes, but it seems likely that annual and daily variations in

temperature might also play a role, alongside maximal habitat temperatures, in

defining thermal tolerance (Brown & Cossins, 2011); therefore the thermal tolerance

of corals are defined not only by their maximum temperature exposure, but also by the

amount of solar radiation experienced (Fitt et al., 2001). The demonstration of

acclimatization of corals to thermal stress appears to involve several processes,

including “the replacement of bleaching susceptible zooxanthellae by genetically

distinct, bleaching resistant zooxanthellae, shifts in the dominant members of

zooxanthellae populations in corals which host multiple clades or types of algae, and

changes in the physiological/biochemical traits of both the coral host and/or its

zooxanthellae” (Brown & Cossins, 2011).

Early studies by Coles and Jokiel (1978) investigated the acclimation of corals to

thermal stress; including the evaluation of the effects of thermal effluent from a power


12

plant on corals in Hawaii. They found that Montipora verucosa was capable of

displaying thermal acclimation to temperatures of 1-2°C above the summer maximum

temperature, and that Montipora verucosa was able to tolerate fluctuating temperature

regimes. In addition to this, Coles et al. (1976) had earlier found that sub-tropical coral

species exhibited an upper lethal thermal limit which was 2 ̊ C lower than equivalent

species found in tropical locations. Similarly a study conducted on the Great Barrier

Reef, revealed the summer bleaching threshold for Pocillopora damicornis to be 1 ̊ C

higher than that of the winter bleaching threshold for the same species (Berkelmans &

Willis, 1999). In a later study, Berkelmans (2002) determined a correlation between

cross-shelf and latitudinal differences in bleaching thresholds and specific temperature

regimes on mid and outer-shelf reefs in terms of thermal adaptation on scales of 10-

100km on the Great Barrier Reef (Brown & Cossins, 2011).

It has been demonstrated in studies that reduced susceptibility to coral bleaching and

increased thermal tolerance limits may be attributed to pre-conditioning e.g. unusually

high solar radiation exposure of corals in months leading up to a seasonal maximum

temperature. This anomaly was observed in Phuket, Thailand in 1997 and 1998 when

it was found that the variables of temperature and solar radiation were considerably

higher than temperatures which were previously recorded during the extensive

bleaching periods in 1991 and 1995 (Dunne & Brown, 2001). The reduced bleaching

condition which was observed in 1997 and 1998 in this Indian Ocean ‘warm pool’

location depicted improved thermal tolerance, despite the onset of gradually rising

temperatures over 60 years. In addition to this no major bleaching events on the scale

of the 1991 and 1995 events were reported in recent years.

Increased thermal tolerance was also seen in three major coral genera (Acropora,

Pocillopora, and Porites) on the Great Barrier Reef in 2002 (Maynard et al., 2008).

Similarly this study found that that the prevalence of bleaching was 30-100% lower in

2002, when compared to the extensive bleaching event experienced in 1998, despite

the incidence of significantly higher levels of solar irradiance in 2002 compared to the

1998 event. It was stated that “prior experience of solar radiation before the 2002 event

and selective mortality of less tolerant genotypes, as a result of the 1998 bleaching ,

were not considered to be significant in explaining the observed increase in thermal

tolerance of corals” (Brown & Cossins, 2011). Conversely, the study suggested that


13

physiological acclimatisation, symbiont shuffling, trophic plasticity and/or

heterotrophic feeding may have been possible mechanisms leading to the improved

coral thermal tolerance seen in 2002 (Maynard et al., 2008).

The temperature tolerance of Goniastrea aspera colonies in Phuket, Thailand in

conditions of high irradiance was reported to be partly attributed to high levels of stress

proteins and antioxidants in the coral host, along with improved xanthophyll cycling

in the zooxanthellae (Brown & Cossins, 2011). The thermal tolerance ability of

Goniastrea aspera is also largely influenced by the fact that it hosts Clade D

zooxanthellae, a genotype which is acknowledged as the most thermally tolerant

zooxanthellae known to date (Rowan, 2004). The thermal resistance properties of this

genotype is clearly evident in a study whereby the branching coral Acropora millepora

which hosts both Clade C and Clade D zooxanthellae, was able to harness increased

thermal tolerance in terms of 1-1.15 ̊ C, by altering its dominant symbiont Clade to

Clade D zooxanthellae (Donner et al., 2005).

1.6 Lagoon temperature mediation mechanisms and near-shore reefs

Near shore local coral species may be well adapted to deal with variation in sea surface

temperature. In support of this notion, McCabe et al. (2010) formulated a conceptual

model demonstrating changes in mean lagoon temperature and the significance of

solar-tidal phase in lagoon heating. The findings of this aforesaid study state that

midday and midnight tides produce considerable temperature extremes in that of

shallow water, however, the presence of prevailing ocean currents divert these bodies

of lagoon water away without facilitating localized mixing (McCabe et al., 2010).

This strongly influences the temperature variation of lagoon water through the

offsetting of cooled and heated regions with that of moderate and temperate water

analogous with that of ideally natural conditions. In addition to this the presence of

internal tidal “bores” are also instrumental in alleviating the onset of thermal stress for

near-shore coral reefs from increased Sea Surface Temperature.

This is possible through the relocation of cooler, and more saline oceanic water from

higher regions located farther offshore. This relocation has been shown to occur at

depths greater than 50 meters over cross-shore distances and over 100’s of meters into

warmer less saline waters which are of 20 meters in depth and less (Storlazzi et al.,


14

2013). These cooling internal tidal bores are remarkable in that they serve to protect

shallow near-shore coral reefs from high sea surface temperatures and coral bleaching

while also simultaneously serving as a conduit for supplying food to corals which have

been subjected to thermal stress through ultra violet radiation; and resultant low

salinity levels through this temperature increase. These bores also aid in increasing the

genetic diversity and resilience of near-shore reefs by providing coral larvae for

recruitment from that of deeper off-shore reefs. These occurrences which are generated

when internal waves break at the leading edge of the internal tide, have been found to

be prevalent in coral reefs worldwide (Storlazzi et al., 2013). A prospective project

proposed by the Pacific Centre for Environment and Sustainable Development

(PACE-SD) at the University of the South Pacific aims to quantify internal waves in

Fiji waters (VERTemp Project).

Evidence of near-shore coral reef resilience is also supported by observations showing

that inshore temperature conditions present on that of shallow coral reefs differ greatly

from temperatures observed off-shore. This is reportedly attributed to increased

turbidity as a result of close proximity to landmasses and greater cloud cover; factors

which markedly reduce irradiance and the potential for bleaching. Bays, lagoons and

estuaries are spared from an increase in sea surface temperature due to intervening

factors of land mass, influence of inshore topography on wave action, and changes in

wind conditions and currents in near-shore reef habitats.

Chromophoric Dissolved Organic Matter (CDOM) was shown to lower coral mortality

due to bleaching in severely turbid waters in the Gulf of Kutch, Sri Lanka, whereby,

this dissolved organic matter has shown to absorb UV radiation considerably more

strongly than particulates such as detritus and phytoplankton, along with that of visible

radiation. This holds great significance for managing UV penetration in near-shore

reef areas (Jokiel & Brown, 2004). It has been acknowledged in previous studies,

however, that CDOM adversely affect the operation of ecosystems, with sewage and

river effluent material bringing about localised impacts (Dupouy et al., 2014). The

implementation of a Marine Protected Area could also serve to mitigate and reduce the

stress associated with sedimentation of near-shore reefs through the establishment and

facilitation of prolific populations of herbivorous fish. In this way the fish species

would abate algal growth to a certain extent and allow for the recovery of sediment


15

affected coral populations through the provision of lag time necessary for the corals to

recover (Halpern et al., 2013).

Cold-water upwelling processes on a small localized scale also have the potential to

negate the bleaching effects of bodies of heated sea surface water, and can provide

refuges for corals from thermal stress. Bridge et al. (2013) reported lower coral

mortality levels in an area which experienced periodic episodes of cold water

upwelling, and also experienced and reported on rapid upwelling-driven temperature

drops of 10° Celsius off the west coast of the Similan Islands. A condition known as

the “Island Mass Effect” can also counteract the process of bleaching through turbulent

and vertical mixing of water present on the leeward point of islands which experience

strong currents. A cooling effect is then seen through the upwelling of cool deeper

waters through this vertical mixing. There are also physical factors which decrease

light stress such as the role of Photosynthetically Active Radiation (PAR) (400-700nm

wavelengths) which intensify photo inhibition brought about through heat stress. This

is brought about through high levels of incident solar energy which cause sea surface

temperatures to rise (Jokiel & Brown, 2004). The physical location of a reef can also

significantly influence its resilience through the aiding of larval dispersal. In this

situation, favourable current patterns work to deliver coral larvae throughout certain

locations or to an area that hosts ideal physical conditions conducive to optimal coral

growth and development (Crabbe, 2010).

1.7 Coral recruitment in resistance and resilience after disturbance

Successful coral recruitment is a vital prerequisite for the recovery of corals from

disturbances i.e. bleaching, storms etc., (Fabricius, 2011). Successful coral recruitment

itself depends on several factors: the availability of crustose coralline algae on suitable

substrate which provide cues for larval settlement, the availability of coral larvae from

an external reference population, or larvae from the local brood (self-seeding). The

amount of available light intensity and spectral quality also affects the settlement

density of larvae from zone-specific coral species (Baird et al., 2003). Corals are very

vulnerable in their recruitment stage to pollution as newly settled coral larvae and

young colonies are extremely sensitive to adverse variables not conducive to their

survival. It is reported that very little settlement takes place on sediment covered


16

surfaces, and that the tolerance of coral recruits to sedimentation is at least one order

of magnitude lower than that of adult corals (Fabricius, 2011).

1.8 Coral reef status, resilience, and recovery in the Fiji Islands

Fijian coral reefs appear to display remarkable resilience to sudden catastrophic events

(Sykes & Lovell, 2007). After the major coral bleaching event of 2000 and 2002, it

was reported that affected reefs were making a strong recovery with increasing

densities of Acropora recruits observed at sites around Suva (Wilkinson, 2002). An

interesting point mentioned by (Sykes & Lovell, 2007) was that following the

recovery period, Fijian reefs showed a greater life-form diversity of Acropora and non-

Acropora corals than was present before the bleaching disaster (See Figure 1.0). The

decline in coral cover due to the bleaching events of 2000 was ascribed to the mortality

of faster growing Acropora corals, however, the rapid recolonization and growth of

acroporid corals on affected reefs lead to increasing coral cover; with some affected

areas reaching pre-disturbance levels by 2007, and some sites displaying 80% live

coral cover by 2006 (Morris, 2009). Current work in Fiji on coral bleaching and

recovery in the Fiji Islands, includes work done by (Whiteside, 2015) and conducted

at the University of the South Pacific.

Figure 1.0 Average coral cover at two depth categories from core survey sites on

Fijian Reefs; depicting a clear recovery trend from the 2000 bleaching event and Crown-of-Thorns starfish. Source: (Wilkinson, 2008)

The advent of cyclones during this period also assisted coral recovery by lowering sea

surface temperatures and clearing benthic substrate for coral settlement. This level of


17

recovery accredits Fiji’s coral reefs with the confident potential of strong resilience

and relative good condition. The Status of Coral Reefs of the Pacific: 2011 handbook

assigns a “STABLE-High Confidence” status to Fiji reefs in terms of coral reef status,

stating “Long-term surveys from many sites show that, while reefs are affected by a

variety of disturbance events, live coral cover has been increasing to pre-disturbance

levels, suggesting relatively stable coral cover over the long term. There is little

evidence of widespread and prolonged stress, damage, or loss of coral cover at the

reefs surveyed”. In terms of coral reef health and resilience The Status of Coral Reefs

of the Pacific: 2011 handbook assigns an “evidence of change - medium confidence”

status stating “Good, long-term information on Fiji’s coral reefs shows rapid recovery

(within 5 years) from significant declines in coral cover, indicating strong resilience.

Reefs appear to be relatively intact with little evidence of widespread, long-term

changes in reef communities or processes” (Chin et al., 2011). Sykes and Lovell

(2007) state that although Fiji’s reefs have recovered strongly from mass bleaching

incidents in 2000 and 2002, more research is required to adequately understand the

mechanisms promoting this recovery.

1.9 Rationale for study

A preliminary reconnaissance trip to the primary study site (Dynamite Hut) for this

study, revealed the persistent and healthy presence of reef building corals of the genera

Acropora, Porities, and Pocilliopora despite the constant stressors of high freshwater

influx through storm water drains, high turbidity through large sedimentation input

and continuous resuspension, oil and chemical pollution from the Suva Wharf and

industrial area in Walu Bay, and confirmed eutrophication through sewage input at the

Rewa River mouth and Nabukalou Creek entrance in Suva. In this regard a seasonality

study conducted on a yearly time scale would ideally serve to provide an in-depth view

into the variability in conditions experienced at the locality during alternating seasons,

and coral response through varying intensities of anthropogenic pollution experienced

on an annual basis.

A coral reef health monitoring study on coral assemblages present adjacent to the Walu

Bay industrial area would be very important in attempting to understand the influential

roles of key environmental variables in the persistent presence of reef corals in this

location, and in the midst of major anthropogenic stressors. This study would thereby


18

serve to generate valuable data on coral health and the magnitudes of associated

environmental variables in a highly polluted and stressed location situated in

immediate proximity to an industrial area and urban city mainland; as no previous

study of this nature and magnitude has been conducted in the Suva foreshore area to

date.

1.10 Purpose and structure of this thesis

The main purpose of this study will be to investigate coral health and local

environmental variables in the designated inshore anthropogenically-stressed primary

site (Dynamite Hut), and an offshore control site (Dennis’ Patch); which hosts a more

ideal coral reef ecosystem relatively devoid of major anthropogenic stressor

influences. This will be achieved using proven methods employed in routine coral

monitoring and through the conduction of a year- long investigation in order to acquire

and interpret data based on coral response in alternate seasons.

Hypotheses:

i. Coral cover variation is significantly higher in an anthropogenically-stressed site

between successive monitoring months, compared to a control site.

ii. Coral species diversity and abundance will be higher in the control site in

comparison to the Dynamite Hut site.

iii. Coral spat species diversity and abundance will be significantly higher in the

control site, in comparison to the Dynamite Hut site.

iv. Sedimentation and Particulate Organic Matter content in sediment will be

significantly higher in the Dynamite Hut site in comparison to the control site.

v. Temperature, light intensity, and Photosynthetically Active Radiation will be

significantly lower in the Dynamite Hut site in comparison to the control site.

vi. Salinity and Dissolved Oxygen values will be significantly lower in the Dynamite

Hut site in comparison to the control site.


19

The aforementioned hypotheses served as the basis for forming the following

objectives:

1. To identify and compare the health and growth phases of dominant coral species

(Order Anthozoa), between the polluted Walu Bay study site and the more

natural reef system at the Dennis’ Patch Reef site

2. To determine the recruitment rates of corals at the primary study site in

comparison with corals at the control site in order to identify post-settlement

resilience properties.

3. To construct a coral health Time Line at the primary study site and at the control

site in order to compare and contrast the magnitudes of relevant ambient

environmental parameters.

1.11 Thesis structure

This thesis is organised into five chapters.

Chapter 1 comprises of a general introduction which deals with the economic

importance of coral reefs, and threats to their sustainability on that of a global scale.

Insight into the subsistence and commercial exploitation of coral reefs on a national

scale in the Fiji Islands is also given, with emphasis also placed on anthropogenic

threats to near shore coral reef sustainability in the Fiji Islands.

Chapter 2 evaluates the health and growth phases of dominant coral species between

a polluted inshore primary site, and an offshore control site through permanent quadrat

monitoring. Coral cover and other major health category percentages was determined

from photographic data acquired using this method and between study sites; along with

individual coral species diversity and abundance using image analysis software Coral

Point Count with Excel extensions (CPCe v. 4.1).

Chapter 3 describes coral larval recruitment rates and coral spat diversity present

between study sites in order to identify coral tolerance and resilience to anthropogenic

environmental disturbance. Coral spat abundance was determined using two-month


20

settlement tile collection intervals, with six-month settlement tile collections intervals

describing coral Family diversity between sites for the duration of one year.

Chapter 4 documents annual sedimentation load present with each study site

environment, along with the Particulate Organic Matter (POM) content composition

in sediment matter. This latter evaluation attempted to provide insight on the water

quality and general health of each study site in terms of phytoplankton proliferation in

nutrient rich conditions. Average Daily Sediment Trap Collection Rates (ADTCR) are

described for both study sites in order to ascertain daily sediment influxes experienced

within individual study site environments.

Chapter 5 investigates the influence of certain key ambient environmental parameters

throughout changing seasons. This section describes recorded temperature, light

intensity, salinity, and dissolved oxygen magnitudes between sites in order to identify

potential stressor variables and their influence on coral reef health. Correlation

analyses were made between light intensity and sedimentation load within sites, in

order to examine water column turbidity and light availability for coral photosynthesis

in terms of Photosynthetically Active Radiation (PAR).

Chapter 6 provides a general summary of the key findings of this study, and provides

a number of recommendations for advancing this study in terms of elucidating the

genetic mechanisms, and the resilience and adaptive responses of corals to

environmental stressors which allows them to persist in heavily polluted areas. In

addition to this, suggestions are provided on how to further this study on that of a wider

scope, and the possibility of implementing potential ideas for doctoral research.


21

1.12 Study area’s

Primary study site: Dynamite Hut, Walu Bay, Suva foreshore

The primary study site (PIS primary inshore site hereafter), is located in very close

proximity to the industrial area in Walu Bay, Suva which is a distance of around 375

meters (See Appendix 1.0). The study area is situated directly adjacent to a World

War II concrete hut structure informally termed ‘Dynamite Hut’, with the depth profile

ranging from 1.64 to 2.15 meters. Numerous coral assemblages have been observed in

this immediate area following an exploratory dive to determine study feasibility.

Corals seen in the area include species from the genus Acropora, Porites, Fungia and

Pocillopora (See Appendix 1.1). Additionally, through initial discussions with a coral

biologist who is quite familiar with the study area, it was learned that the area where

the Dynamite Hut is located was previously “a luxuriant reef ecosystem, but the

remnants of which are now desperately hanging on and dwindling” (Lovell, E,

personal communication).

Figure 1.1 Photograph of the “Dynamite Hut” structure taken on 15/07/14


22

General and specific location of Primary Study Site

Figure 1.2 General location of the ‘Dynamite Hut’ structure outlined

in red insert and in relation to Suva Harbour (above), and geo-referenced permanent quadrat locations in aerial photograph (below)


23

Listed below is a table containing the latitudinal and longitudinal coordinates for the

specific locations of individual permanent quadrats in the primary study site. These

coordinates were obtained using a hand held Global Positioning System unit.

Table 1.0 Coordinates for individual permanent quadrats

Quadrat No. Latitude Longitude 1 18°09.056S 178°27.255E 2 18°07.452S 178°25.518E 3 18°07.453S 178°25.517E 4 18°07.454S 178°25.512E 5 18°07.456S 178°25.508E

This location receives very high sedimentation from possible resuspension of benthic

sediment and land runoff, and has visible oil pollution present on the surface of the

water (see Fig 2.4). There is also the possibility of effluent discharge from yachts

berthed in the immediate vicinity of the study site, and on previous data collection trips

workers from the floating dry dock ‘IMEL Naisiqasiqa’ (which is situated directly

adjacent to the study site), have been observed dumping anti-fouling paint and other

compounds into the water. These substances are known to contain lead and other heavy

metals which are toxic to corals.

Figure 1.3 Copious amounts of possible diesel or petroleum oilobserved on water surface in immediate study area.Photograph taken on 28/10/14


24

Base-line study site: Dennis’ Patch Reef, Nasese foreshore, Suva

Dennis’ Patch (COS control offshore site hereafter), is characterized as an offshore

lagoon patch reef in the Suva region located at 18 10’S Latitude and 178 25’E

Longitude. It holds a maximum depth of five meters and is designated as a slope in

terms of reef zone (Morris & Sykes, 2009). This area was selected as a base-line

comparative study site due to the fact that it holds a similar depth profile as the primary

study site, is not subjected to as many anthropogenic stressors as the primary study

site, and is also a more ideal and natural reef ecosystem.


25

General and specific location of control study site

Figure 1.4 General location of Dennis’ Patch reef outlined in red insert and in relation to Suva Harbour (above), and geo-referenced permanent quadrat locations in aerial photograph (below)


26

The following table contains the latitudinal and longitudinal coordinates for the

specific locations of individual permanent quadrats in the baseline comparative study

site. These coordinates were obtained using a hand held Global Positioning System

unit.

Table 1.1 Coordinates for individual permanent quadrats

The depth profile for the base-line site is from 1.5-2.0 meters for the shallow region,

and 3.0-4.0 meters for the deepest area. The area has very low turbidity and excellent

water clarity. A high diversity of reef building corals from various genera are present

including Acropora, Porities, Pavona, and Pocillopora. There are also numerous

species of reef fish and benthic invertebrates seen in the reef area.

Quadrat No. Latitude Longitude 1 18°10.051S 178°25.270E 2 18°10.050S 178°25.272E 3 18°10.050S 178°25.263E 4 18°10.048S 178°25.269E 5 18°10.055S 178°25.256E

Ronal Lal CHAPTER TWO

27

CHAPTER TWO

EVALUATING CORAL COVER AND SPECIES DIVERSITY THROUGH

MONTHLY PERMANENT PHOTO- QUADRAT MONITORING

2.1 Introduction 2.1.1 Long term monitoring and the permanent photo quadrat method

“Long-term monitoring is the repeated surveying of organisms or environmental

parameters over time in order to help us understand a variety of natural processes; with

monitoring programs also providing information on the abundance of the biota, the

diversity of the site, the condition of particular habitats, and changes in the

environment” (Rogers et al., 2001). The permanent photo quadrat method is primarily

employed for the purpose of monitoring the biological condition, mortality and

recovery phases, growth, and recruitment of corals in that of a permanently affixed

quadrat which is typically located at a depth of three meters on the reef slope (English

et al., 1997).

This method involves the capturing of still photographs of a fixed quadrat, which is

later analysed in the laboratory, and is extremely useful for observing temporal

changes in shallow macro benthos communities, estimating coral percent cover, the

diversity of species and their relative abundance, and density and size (Hill &

Wilkinson, 2004). It is envisaged that this study will produce noteworthy data worthy

of conservation efforts, as it is acknowledged that the generation of long-term data is

instrumental in helping us to predict the effects of human activities on ecological

processes; and without which we cannot make appropriate decisions on whether and

how a natural environment needs to be managed (Rogers et al., 2001)

2.1.2 The significance of coral cover

Coral cover is defined as a measure of the proportion of reef surface covered by live

stony coral instead of sponges, algae, or other organisms (McField & Kramer, 2008).

Scleractinian corals which are also known as hard or stony corals form the general

foundation of the reef framework, and are instrumental in providing the infrastructure

for critical habitat niches occupied by numerous organisms. The estimation of coral

cover is a routine monitoring parameter included in reef health monitoring programs,


28

and is considered a significant measure of the general health of a reef system. It is

acknowledged that a typically healthy reef would demonstrate attributes of relatively

high percentages of coral cover, a low percentage of fleshy macro algae, and that of a

moderate percentage of calcareous algae, crustose coralline algae, and short turf algae.

A study evaluating the status of reefs over a 20 year period and involving 60 sites

classified a coral cover percentage of more than 20 percent as “good”, with the

inclusion of low incidences of recent coral mortality, and high a number of coral

recruits (Morelock et al., 2001).

2.1.3 Coral cover estimates using photo-quadrats

A quadrat used to estimate coral coverage or coral health usually consists of a gridded

frame, which is either placed randomly at a certain locality, or is deployed repeatedly

at a pre-established study area through the placement of permanent reference points

i.e. iron pegs. In this way, the photographic series can be consecutively repeated in

order to record coral cover changes over a certain timespan. The permanent photo

quadrat is divided into several sub-quadrats which are individually photographed using

an underwater camera, and that of a frame for ensuring a uniform distance from the

substrate for all successive photographs. The percentage cover of coral species within

each sub-quadrat photograph is then estimated using a purpose-specific software such

as Coral Point Count (CPCe), with each sub quadrat photograph being analysed

cumulatively in order to generate a total percentage of coral cover within the entire

photo-composite quadrat.

The CPCe program is a Microsoft Windows based software which allows for the

determination of coral cover through the processing and analysis of photographs. The

program works by allowing for the calibration of each image, and by assigning a pre-

determined number of spatially random points on an image; with the features

underlying each point being user-identified thereafter. Following this, coverage

statistics can then be calculated and stored in Microsoft Excel spreadsheets for further

interpretation and analysis (Kohler & Gill, 2006).

The permanent photo quadrat monitoring method was considered to be ideally suited

for the conditions present in both of the selected sites in this study; as the depth profile

for the primary study site and baseline site range from between 1.8-3.2 meters and are


29

both located in the fore-reef zone. Moreover, the permanent photo quadrat method is

considered suitable for small-scale questions, and to follow the fate of individual coral

colonies; as is one of the premier objectives of this investigation (Hill & Wilkinson,

2004). This method also provides a logistical solution for addressing the other aims

included in this investigation, as this study proposes to observe and document coral

health and growth characteristics, coral settlement abundance and diversity patterns,

and site in-situ sedimentation rates. These variables are to be assessed on a monthly

period, with a general comparison to be drawn between a heavily stressed in-shore reef

environment which is located in very close proximity to the major urban city of Suva,

and that of a more ideal reef ecosystem located farther off-shore.

2.1.4 The use of the permanent photo quadrat method

Permanent photo quadrat monitoring is considered advantageous due to the fact that it

provides detailed and extensive information relating to a series of temporal changes in

individual coral colonies, along with coral recruitment phases in a specifically mapped

area. In relation to other quantitative sampling methods, the quadrat technique allows

for the rapid and cost-effective acquisition of data from the field, and is significantly

complemented by the provision of cost-effective computer software programs which

are now readily available to facilitate image processing. Permanently affixed photo

quadrats also generate data with the highest statistical power relative to visual quadrats

or video transects, can be undertaken and monitored by non-specialists, and produce

qualitative data in the form of photos which can be used to complement data presented

in graphs.

For coral cover monitoring an underwater camera is mounted on a specially

constructed tripod stand in order to ensure uniform distance from the substrate being

sampled, and a series of sub-quadrats are photographed in order to generate a detailed

photo-composite of the entire quadrat. The forming of sub-quadrats ensures that a high

level of image detail is acquired for accurate analysis, which would not otherwise be

possible through the photographing of the entire quadrat in a single frame. Successive

sampling of the permanent quadrat is undertaken in order to observe and record

changes in the health and growth of the relevant coral communities.


30

The disadvantages of the permanent photo quadrat method includes the difficulty

associated with the identification of small coral colonies in photographs without

detailed resolution and where large or abundant soft coral species often obscure the

presence of other species. It has also been acknowledged that large branching corals

e.g. Acropora palmata are difficult to sample using the quadrat method. The presence

of parallax error brought about by bottom substrate relief and the uneven surface of

many coral reefs is not taken into account, with this method also being very equipment

and time intensive; which is made more difficult in challenging conditions i.e. strong

currents. In addition to this, the quadrat technique grossly underestimates the coverage

of certain coral species which are oriented primarily in in the vertical plane (e.g. soft

corals); due to the fact that quadrat sampling only produces data on a two-dimensional

surface, with relatively flat surfaces required for photography.

Specific computer software is also required for photo-analysis purposes, where

measurements are determined through digitization or point sampling, with the task of

processing photographs for coral cover analysis also being very labour intensive. There

is also a risk of reef damage where the quadrat frame may lie atop of fragile coral

forms. An inaccurate representation of the general reef condition may also be acquired

through this method as only small areas are sampled and interpreted (Hill & Wilkinson,

2004).

2.1.5 Challenges involved in image analysis

The processing of images acquired through permanent photo-quadrat monitoring also

present certain noteworthy disadvantages. A recent study by (Jokiel et al., 2015) who

compare nine coral survey methods at various reef sites in Kaneohe Bay, Hawaii,

found the “classic” visual-estimate quadrat method to be significantly more efficient

than other methods in terms of the detection of a greater number of coral species. This

was found to be attributed to the fact that the classic quadrat method generally involves

“close and direct observation of the corals by a diver”, thereby aiding in the detection

and identification of certain coral species i.e. Pavona varians and Fungia scutaria

which typically grow in crevices and shaded areas, and which are often non-evident

on image analysis.


31

The authors also found that closer evaluation by a diver of the Montipora patula

species allowed for ease of recognition, which is not often differentiated from

Montipora capitata in photo images. This demonstrates the effectiveness of the visual-

estimate quadrat method in real-time, but also serves to highlight the limitations of the

permanent photo-quadrat method, whereby, the presence of certain cryptically settled

coral species can often be overlooked during the analysis of the image itself. Although

the photo-quadrat method is considered time consuming in terms of photo analysis,

and does not take into account parallax error in terms of bottom relief, it is, however,

strongly recommended for coral monitoring programs as it can provide accurate

information on reef cover, provides a permanent record of the coral reef and facilitates

future surveys of a pre-determined area, and is a powerful tool for training new

scientists; which is especially relevant in the Pacific context.

2.2 Research Objectives

The following hypotheses were formulated in order to encompass the nature of

research to be conducted in this chapter.

i. Coral cover variation is significantly higher in an anthropogenically-stressed site

(PIS) between successive monitoring months, compared to a control site

ii. Coral species diversity and abundance will be higher in the COS in comparison to

the PIS.

The following objective was devised in order to test the aforementioned hypotheses:

i. To identify and compare the health and growth phases of dominant coral

species (Order Anthozoa), between the polluted Suva Foreshore study site and the

more natural reef system at Dennis’ Patch Reef site under pre and post-sewage-

discharge conditions.

2.3 Methodology

The following sections indicate the various types of equipment, field techniques, and

laboratory analytical procedures that were employed in the attempt to determine coral

cover, and species diversity and abundance rate at both of the designated study sites.


32

2.3.1 Portable photo quadrat construction

The 2×2 meter portable quadrat used for field data collection was constructed from

(four) two meter lengths of PVC pipe which were 20mm in diameter. PVC pipe elbow

joints were used to connect adjoining two meter sections of PVC pipe in order to form

a square. The two meter sections of PVC were drilled throughout with holes at 0.5

meter intervals in order to accommodate lengths of nylon rope spanning the entire

width of the quadrat interior; and which facilitated the forming of 16 sub-quadrats

within the quadrat. Numbered underwater tags were then attached to the top left hand

corner of each sub-quadrat (See Figure 2.0).

Figure 2.0 Assembled 2×2 meter portable quadrat

2.3.2 Camera tripod stand construction

A camera tripod stand was constructed according to a design demonstrated in English

et al. (1997) in order to ensure a uniform distance from the substrate, and a specific

photo coverage of 0.5m 2 for each sub-quadrat being sampled. The frame was

fabricated by welding together sections of ¼’’ iron rods to form the general frame of

the tripod stand, with a thin aluminium plate forming a platform for camera placement

at the top of the assembly, along with a circular opening at the centre of the plate in

order to accommodate the camera lens. The height of the tripod stand ensured a

distance of 60mm from the substrate, which was a deviation from the original


33

specification mentioned in English et al. (1997) of 80mm; which was done in order to

account for increased turbidity observed in the PIS (See Figure 2.1).

Figure 2.1 Lateral view (Left), and top view of the tripod camera stand (Right)

2.3.3 Permanent quadrats establishment

Five permanent quadrats were established in each study site through the driving of

(four) 3/8’’ rebar iron markers into the substrate with a 4kg iron hammer, and at each

corner of the inside of the portable quadrat after placement on selected coral colonies.

Each rebar iron marker was 1.5 meters in length with the bottom end cut at an oblique

angle in order to allow for ease of insertion into the substrate, affixed with a bright red

plastic tag for ease of relocation, and protruded 0.5 meters from the substrate after

insertion. The top left hand marker of each permanent quadrat was affixed with an

aluminium tag which was punched with holes specifying the particular quadrat

number. In each study site Permanent Quadrat 1 was established in the shallowest

depth, with successive permanent quadrats being established in incrementally deeper

depths down the reef slope. A length of rope was then attached to one of the rebar iron

markers of each permanent quadrat, in order to allow for ease of relocation during

successive monitoring trips.

2.3.4 Monthly monitoring

For monthly monitoring in each study site, the portable quadrat was assembled

underwater and placed on each permanent quadrat station using the permanent


34

placement markers, and laminated A4 sheets of photographs displaying the correct

orientation of the quadrat as a guide. An Olympus Tough TG2 underwater digital

camera with an attached FCON-T01 Fisheye Converter lens was then placed atop of

the camera platform of the tripod stand, with the tripod stand then being placed exactly

atop of each sub quadrat and photographed. Sub-quadrats were photographed in a left-

right-left-right-left manner until all 16 sub-quadrats were photographed. This

procedure was then repeated for all remaining permanent quadrats.

It was endeavoured to keep the sampling dates for each study site as close as possible,

however, due to unforeseen weather conditions the sampling dates for each study site

sometimes deviated from one another by a factor of a few weeks at a time. In addition

to this, sampling could not be undertaken in both study sites for the period spanning

December 2014 – January 2015 due to a national environmental disaster which had

arisen due to a major raw sewerage spill into the Suva harbour area on December 6,

2014. An environmental emergency was declared by the Fiji Government on 3rd

January 2015, and entry into the study areas included in this study was prohibited.

Monitoring was resumed at the earliest allowable opportunity, which was in February

2015.

2.3.5 Image processing and analysis

Images collected from monthly monitoring trips were successively catalogued and

stored in a hard disc drive for later retrieval. For coral species identification in each

permanent quadrat and for both study sites, a coral identification key was used. Coral

Point Count with Excel extensions (CPCe v.4.1) software was then used to analyse

coral cover statistics in relation to other major categories e.g. macro algae, sand etc.,

as well as coral species abundance and diversity in terms of sub-categories.

Each sub-quadrat image was initially calibrated to scale (50cm×50cm) and then

overlaid with 20 software-generated random points; with the life form features

underlying each point subsequently identified (See Figure 2.2). Processed sub-

quadrat photos were then grouped under their relevant permanent quadrat station and

analysed collectively for coral cover, and coral species diversity and abundance.

Although monitoring was conducted every month for the duration of one year, only

data collected before and after every six months was analysed and used to compare


35

differences in coral cover and species diversity and abundance. This consisted of data

collected directly after site establishment, data collected seven months following site

establishment (lifting of environmental emergency declaration), and data collected

after twelve months of monitoring (conclusion of study). This was in accordance with

standard ecological monitoring practices (Hill & Wilkinson, 2004).

Figure 2.2 A CPCe processed photograph from the PIS: Permanent Quadrat 1 (sub-quadrat 16), showing 20 randomly generated points.


36

2.4 Results and Discussion

2.4.1 Coral cover percentage between sites and monthly trend

A notable difference in total mean coral cover percentage was observed between the

PIS (27.10 %), and the COS (68.33 %) at the start of the monitoring period in month

one (See Table 2.0). A decrease trend in coral cover within each study site was then

observed starting from month one and continuing through to month seven and month

twelve (See Figure 2.3 and Figure 2.4).

Table 2.0 Major categories and respective site abundances. PIS: Dynamite Hut; COS: Dennis Patch

Figure 2.3 Bar graph displaying major category abundance between study sites for months 1, 7 and 12

Major categories

Site and monthly abundance (mean %) Month 1 Month 7 Month 12

PIS COS PIS COS PIS COS Coral Cover 27.10 68.33 20.33 62.86 18.47 56.12 Dead Coral with Algae 8.19 5.89 7.31 10.79 9.25 17.32 Macro algae 5.56 0 25.68 0.06 27.81 0 Sand/Pavement/Rubble 58.20 21.12 47.84 26.09 43.44 25.61 Sponges 0.97 0.50 1.33 1.01 1.02 0.95 Other Live 0.32 0.56 0.19 0.38 0 0


37

2.4.2 Coral cover change within sites

A non-parametric Friedman’s test was performed in order to identify the possible

presence of significant differences in coral cover within each study site, and between

the particular monitoring periods being investigated. This test works by comparing

mean rank values between groups, and specifies how the groups differed. A post-hoc

analysis test is required subsequent to this, as the Friedman’s test only reports on the

presence of overall differences, but does not pinpoint exactly which groups differed

from each other. The following null and alternative hypotheses were therefore tested:

Ho: There is no statistically significant difference in Coral Cover between monitoring

periods within each study site

Ha: There is a statistically significant difference in Coral Cover between monitoring

periods within each study site

PIS

It was found that there was no statistically significant difference (p < 0.165) in coral

cover between the designated monitoring periods for the PIS (See Table 2.1).

Therefore, for this site the null hypothesis was accepted.

Table 2.1 Friedman’s test results: PIS

A non-parametric Wilcoxon’s multiple comparisons test was used as a post-hoc

analysis in order to verify the results of the Friedman’s analysis, and also to confirm

the presence of any significant difference between monitoring periods for the PIS. A

significant difference was found to be present between a pair of observation months

using this analysis. The following hypotheses were therefore coined in order to further

investigate the differences between observations:

Ho: There is no significant difference in mean ranks between pairs of observations

Ha: There is a significant difference in mean ranks between pairs of observations

Month Coral Cover mean rank

Asymptotic significance

1 2.60 0.165 7 1.40

12 2.00


38

Based on the results of the post-hoc analysis it was learned that a statistically

significant difference in mean ranks (p > 0.043), existed between the pair of

observations for month 1 and month 7 in terms of coral cover percentage. There was,

however, no statistically significant difference in mean ranks found between month 1

and month 12 (p < 0.500), and for month 7 and month 12 (p < 0.686). This means that

a significant decrease in coral cover percentage occurred between month 1 and month

7 in the PIS (See Table 2.2). A likely explanation for the decrease in coral cover

observed for this period would be the effects of dredging activity undertaken in Suva

Harbour and in the immediate study site area around 21/11/2014.

As a result of this destructive activity, the effects of heavy sediment resuspension was

observed in all permanent quadrat stations on the aforesaid date, in the form of

observed coral sediment smothering and sporadic mortality. A sediment sum value of

86.26 g.cm 2 was also measured during this period for this site (See Chapter 4, Table

4.0), and supposedly brought about the reduction in coral cover seen on the successive

sampling date on 22/12/14. Major mechanical damage from a dredging bucket to a

large Acropora species colony located in Quadrat 4 caused extensive mortality and a

reduction in coral cover percentage from 33.65 % to 6.67% for this particular station

(See Appendix 1.2). A data logger located in close proximity to this station was also

buried as a result of this destructive activity, and was only retrieved after arduous

digging and searching.

Table 2.2 Wilcoxon’s post-hoc test between observation months The continual decrease in coral cover trend seen in successive months for this site can

be attributed to the sewage spill disaster in Suva Harbour which occurred on the 6th of

December 2014. An increase in the abundance of Macro algae was seen in consecutive

months following the environmental disaster from 5.56% in month 1 to 25.68% in

month 7, and 27.81% in month 12; this increase was most likely due to eutrophication

(See Table 2.0 and Figure 2.2). A slight decrease in the percentage of dead coral

Observation month pairs


1-7 0.043 7-12 0.686 1-12 0.500


39

with algae was observed from month 1 (8.19 %) to month 7 (7.31%), with the highest

percentage recorded for month 12 (9.25%) (See Table 2.0). A decrease in

Sand/Pavement/Rubble from (58.20%) in month 1, to (43.44%) in month 12 was also

seen as this substrate space was gradually encroached upon by the increasing macro

algae percentage (See Table 2.0 and Figure 2.2). The appearance and consistency of

sand substrate in this site was that of dirty, and silt laden in texture.

It can be stated that the inshore relic reef ecosystem present at the PIS is very dynamic

in nature, with wave and current action playing a major role in influencing water clarity

in the area. The location also experiences heavy sedimentation by way of the Tamavua

River mouth, with this outlet also acting as a conduit for periodic freshwater influxes

and consequent variation in salinity. Sediment resuspension is also brought about by

the movement of vessels which are berthed at the Royal Suva Yacht Club which is

located in very close proximity to the study site. Anthropogenic disturbance is very

frequent in the area by way of damage to corals through boat anchors, and littering

individuals who use the Dynamite Hut structure as a recreational shelter. There are

also periodic toxic discharges of diesel fuel, oil, and anti-fouling paint material which

have been observed to be floating on the water surface at various sampling times.

These polluting substances are believed to originate from factories located in the

nearby Walu Bay industrial area, as well as the floating ship repair docks which are

stationed immediately adjacent to the study area.

COS

For the COS a statistically significant difference (p < 0.016) in coral cover between

monitoring periods was revealed after performing the Friedman’s test. The same

hypotheses as mentioned under the Friedman’s test section for the PIS were also

applicable here. Therefore, the null hypothesis was rejected (See Table 2.3).

Table 2.3 Friedman’s test results: COS

Month Coral Cover mean rank


1 2.70 0.016 7 2.30

12 1.00


40

The Wilcoxon’s multiple comparisons test was again used as a post-hoc analysis in

this section after the presence of a significant difference between monitoring periods

had been established through the Friedman’s test; and in order to determine the exact

location of the significant difference. The aforementioned hypothesis applicable to this

analysis, and which was also performed for the PIS, was also relevant to this section.

For the COS, there was found to be a significant difference in means ranks (p > 0.043)

between the pair of observations for month 1 and month 12, and for month 7 and month

12 (p > 0.043); in terms of coral cover percentage. There was, however, no statistically

significant difference in coral cover between month 1 and month 7 (p < 0.144). This

means that the greatest declines in coral cover percentage occurred between month 7

and month 12 in the COS. Visible incidences of coral mortality was observed in the

COS towards the conclusion of the monitoring study, with this occurrence supported

by the increasing percentage of dead coral with algae observed from month 1 (5.89%),

to month 7 (10.79%), and through to month 12 (17.32%) (See Table 2.0). These

patches of mortality were attributed to coral bleaching as a result of high sea surface

temperatures, and coupled with increased amounts of light intensity by way of the high

water clarity seen in this particular study site. These assumptions will be discussed in

more detail in Chapter 5, which examined light intensity and sea surface temperature

magnitudes through monitoring,

This site experienced very low incidences of macro algal outbreaks in comparison to

the PIS with month 1 recording (0%), month 7 (0.06%), and month 12 (0%). This

occurrence was attributed to the high current action experienced and observed in this

area, which played a pivotal role in diverting eutrophic waters away from the

ecosystem. In this regard, a high abundance of coral rubble was observed in this site

compared to the PIS, which is indicative of mechanical damage through current action.

In addition to this, very low incidences of Diadema antillarum Echinoidea species

were found throughout the year long monitoring duration in the COS, in comparison

to the PIS where this species was found to be prolific in number all year around. The

dense concentration of Diadema species in an ecosystem is a reliable indicator of

nutrient rich (eutrophic) and polluted waters, as was observed on a macro-algal

dominated and dead reef in Grenada during the late 1980’s (DeGeorges et al., 2010).


41

The substrate in the COS was mostly dominated by coral rubble and clean carbonate

sand. The percentage of sand substrate space in quadrat stations other than that which

was occupied through coral cover, was very minimal in comparison to the PIS which

demonstrated contrastingly low coral cover (See Figure 2.2). This was evident in the

percentage results for Sand/Pavement/Rubble: month 1 (21.12%), month 7 (26.09%),

month 12 (25.61%) (See Table 2.0).

The offshore reef ecosystem at the COS is an open system which is exposed to a

relatively high amount of current action. This is evident through the presence of a large

amount of coral rubble in this area. There is very little macro algae present in this

location and this site is considered to be a “more-ideal reef ecosystem” in comparison

to the PIS. The amount of mechanical damage or pollution present in this site through

anthropogenic influences is very minimal in comparison to the PIS.

Figure 2.4 Coral cover comparison in study sites


42

2.4.3 Coral species diversity between study sites

A total of 15 different coral species were identified in the PIS, compared to 14 different

species for the COS in the first month of monitoring. In the seventh month 11 different

species were identified in the PIS, with 13 identified in the COS. In month twelve, 15

species were again found and identified in the PIS, with 13 species identified in the

COS (See Table 2.4).

Table 2.4 Coral species percentage of monthly coral cover

Coral species Site and monthly abundance (mean % of

Coral Cover) Month 1 Month 7 Month 12

PIS COS PIS COS PIS COS Acropora elseyi 1.86 0.38 1.09 0.32 0.82 0.31 Acropora hyacinthus 0 0.25 0 0.25 0 0.25 Acropora micropthalma 1.51 2.90 2.88 2.59 1.52 2.64 Acropora millepora 3.73 0 0 0 0.64 0 Acropora nobilis 6.12 0.76 0.76 0.57 0.71 0 Acropora pulchra 0.20 0 0.63 0 0 0 Favites sp. 0.07 0 0 0 0.13 0 Favites halicora 0 0.25 0 0 0.13 0 Fungia repanda 1.77 0.19 2.66 0.38 2.21 0.44 Leptastrea purpurea 0 0.90 0.76 0 0.96 0.06 Millepora tenella 0 13.42 0 12.13 0 10.53 Porites australiensis 0 0 0 0.06 0 0.44 Porites cylindrica 0 2.83 0 2.21 0 2.08 Pocillopora damicornis 2.05 0.56 1.91 0.19 2.67 0.38 Porites lobata 5.39 15.03 6.40 14.39 15.14 5.71 Pocillopora 0.07 0 0 0 0 0 Porites sp. 0.52 0 0 0 0 0 Porites rus 2.19 31.57 1.72 29.57 0.82 23.46 Platygyra sinensis 0 0.06 1.72 0.06 0.06 0.25 Psammocora sp. 0.07 0 0 0.06 0.13 0.13 Pavona varians 0.13 0 0 0 0.25 0 Stylophora pistillata 0.39 0 1.39 0 1.70 0 Turbinaria reniformis 0 0.13 0 0 0 0

A non-parametric Mann-Whitney U Test was conducted on the percentage abundance

of each coral species in order to determine its relative abundance within each study

site, and within each monitoring period. The following null and alternative hypotheses

were therefore formulated in order to investigate the individual species abundances in

each site:


43

Ho: There is no statistically significant difference in coral species abundance between

the two study sites over a twelve month period

Ha: There is a statistically significant difference in coral species abundance between

the two study sites over a twelve month period

2.4.3.1 Acropora species

For the Acropora species present in both study sites, it was revealed that no statistically

significant difference in the abundance of Acropora elseyi, Acropora micropthalma,

Acropora millepora, Acropora nobilis, and Acropora pulchra species existed between

the PIS and COS. The null hypothesis was therefore rejected with respect to these

species. There was however, a statistically significant difference in species abundance

present for Acropora hyacinthus between the study sites; with a higher abundance of

this species seen to be present in the COS based on a higher mean rank value generated

for this site (See Table 2.5 and Figure 2.5).

Figure 2.5 Acropora species abundance between sites and over a twelve month duration


44

Table 2.5 Acropora species Mann-Whitney U test values between sites

2.4.3.2 Porites species

For the Porites species present in both study sites, it was revealed that no statistically

significant difference in the abundance of Porites australiensis, Porites lobata, and an

unidentified Porites species existed between the PIS and COS. The null hypothesis

was therefore rejected with respect to these species. There was however, a statistically

significant difference in species abundance present for Porites cylindrica, and Porites

rus between the study sites. A higher abundance of Porites cylindrica (mean rank =

20.00), was seen in the COS, along with a higher abundance of Porites rus in this site

as well (mean rank = 19.83) (See Table 2.6 and Figure 2.6).

Coral species Significance Mann-Whitney U

Mean Rank PIS COS

Acropora elseyi 0.079 75.00 13.00 18.00 Acropora hyacinthus 0.035 82.50 13.50 17.50 Acropora micropthalma 0.490 99.00 14.60 16.40 Acropora millepora 0.073 90.00 14.00 17.00 Acropora nobilis 0.313 95.50 14.37 16.63 Acropora pulchra 0.150 97.50 14.50 16.50

Figure 2.6 Porites species abundance between sites and over a twelve month duration


45

Table 2.6 Porites species Mann-Whitney U test values between sites

2.4.3.3 Favites species

For the Favites species present in both study sites, it was revealed that no statistically

significant difference in the abundance of unidentified Favites existed between the PIS

and COS. The null hypothesis was therefore rejected with respect to this unidentified

species. There was, however, a statistically significant difference in species abundance

present for Favites halicora species between the study sites. A higher abundance of

Favites halicora (mean rank = 17.50 was seen in the COS compared to the PIS (mean

rank = 13.50) (See Table 2.7 and Figure 2.7).


Mean Rank PIS COS

Porites australiensis 0.150 97.50 16.50 14.50 Porites cylindrica 0.001 45.00 11.00 20.00 Porites lobata 0.183 80.50 17.63 13.37 Porites rus 0.007 47.50 11.17 19.83 Porites 0.150 97.50 14.50 16.50

Figure 2.7 Favites species abundance between sites and over a twelve month duration


46

Table 2.7 Favites species Mann-Whitney U test values between sites

2.4.3.4 Pocillopora species

In terms of the two Pocillopora species present in both study sites, it was revealed that

no statistically significant difference in the abundance of Pocillopora damicornis, and

unidentified Pocillopora species existed between the PIS and COS study sites. The

null hypothesis was therefore rejected with respect to these two categories (See Table

2.8 and Figure 2.8).

Table 2.8 Pocillopora species Mann-Whitney U test values between sites


Mean Rank PIS COS

Favites halicora 0.035 82.50 13.50 17.50 Favites (unidentified) 0.079 75.00 13.00 18.00


Mean Rank PIS COS

Pocillopora damicornis 0.073 90.00 17.00 14.00 Pocillopora (unidentified) 0.490 99.00 14.60 16.40

Figure 2.8 Pocillopora species abundance between sites and over a twelve month duration


47

2.4.3.5 Miscellaneous species

For all of the miscellaneous species present in in both study sites which included

Leptastrea purpurea, Fungia repanda, Platygyra sinensis, Pavona varians, and

Psammocora species; it was revealed that no statistically significant difference existed

in terms of species abundance between sites. The null hypothesis was therefore

rejected with respect to these species (See Table 2.9 and Figure 2.9).

Table 2.9 Miscellaneous species Mann-Whitney U test values between sites

2.4.4 Shannon Weaver diversity indices

Diversity indices are often seen as indicators of the well-being of ecosystems

(Magurran, 2004). The Shannon-Weaver index is a commonly used measure in the

assessment of biodiversity and species richness in ecological literature. It is calculated

as follows:


Mean Rank PIS COS

Leptastrea purpurea 0.490 99.00 14.60 16.40 Fungia repanda 0.073 90.00 17.00 14.00 Platygyra sinensis 0.313 95.50 14.37 16.63 Pavona varians 0.150 97.50 14.50 16.50 Psammocora 0.079 75.50 13.00 18.00

Figure 2.9 Miscellaneous species abundance between sites and over a twelve month duration


48

P i : The proportion of species i in relation to the total number of species

Shannon-Weaver index values typically range between 1.5 and 3.5 in ecological

studies, with the index not normally exceeding a value greater than 4. An increase in

the Shannon index is directly correlated with an increase in the species richness and

community evenness within the ecosystem (Shannon & Weaver, 1949).

Each diversity index for respective monitoring months was calculated using Coral

Point Count with Excel extensions software (CPCe v.4.1), in order to compare and

contrast the diversity of species in each of the two study sites. It was found that the

PIS recorded the highest coral species diversity in each of the monitoring periods in

comparison to the COS (See Table 2.10).

This occurrence would be attributed to PIS reef being seeded with coral larvae from

nearby coral reef ecosystems which host large coral species diversity. Favourable

current patterns within Suva Harbour would play a major part in facilitating the

transport of larvae to the stressed reef system observed at the PIS. A much larger

diversity than that which was observed could be possible in this site, however, the lack

of sediment-free settlement substrate serves as a major impediment to coral settlement

and survival. It was surmised that coral larvae transported to this site originated from

areas around the nearby Fish Patch reef, as well as the Muaivuso Marine Protected

Area; reef ecosystems which are known to contain a fair amount of coral species

diversity. Conversely, the COS is an isolated reef system, which would rely on the

transport of coral larvae for recruitment and subsequent settlement.

Table 2.10 Coral species diversity between sites

Month Shannon-Weaver Index (Coral Cover) PIS COS

1 1.34 0.69 7 1.30 0.68 12 1.49 0.72


49

2.5 Conclusion

2.5.1 Coral cover abundance: site comparison

Coral cover percentage in the PIS in the initial month of monitoring was significantly

lower in comparison to coral cover in the control site; which is a stark reflection of the

reef ecosystem health present in each study site. A general decline in coral cover with

respect to both study sites was observed throughout the monitoring period. The PIS

saw the greatest decline in coral cover between month 1 and month 7 of monitoring,

with the greatest increase in macro algae percentage also seen during this aforesaid

period. This occurrence was attributed to the sewage spill event which occurred in the

Suva Harbour on 6 December 2014.

Significant loss in coral cover in quadrat 4 in the PIS was a result of mechanical

damage through dredging activity in the area, which also brought about copious

sediment resuspension in the site, and consequent sporadic coral mortality. Coral cover

did not decrease significantly from month 7 to month 12 in this site, with the presence

of visible coral recruitment serving as a testament to the resilience of this stressed relic

reef ecosystem. A large number of Diadema Echinoidea species are present in this site,

which indicates the presence of eutrophic and nutrient rich waters.

The COS experienced the greatest decline in coral cover between months 7 and 12.

This site did not experience a high incidence of macro algal presence in any period of

monitoring, however, the presence of high current action was evident in this site

through a high coral rubble percentage observed through successive monitoring

months. Sporadic bleaching was observed in this site towards the conclusion of the

study and this can be attributed to the sewage spill disaster in December 6 2014.

2.5.2 Coral species diversity and abundance: site comparison

The stressed PIS recorded higher species diversity in all monitoring months in

comparison to the COS. In terms of individual coral species abundances, the PIS

recorded a majority of species abundances which were not statistically different from

the abundances of similar species seen in the COS; except for Acropora hyacinthus,

Porites cylindrica, Porites rus, and Favites halicora. Both study sites displayed the


50

highest species diversity in month 12 of monitoring, however, the PIS still presented

with a greater diversity index value in this period as well.

Ronal Lal CHAPTER THREE

51

CHAPTER THREE

DETERMINATION OF CORAL RECRUITMENT RATES IN TERMS OF

FAMILY ABUNDANCE AND DIVERSITY OVER A SEASONAL

TIMESCALE: A SITE-COMPARISON STUDY

3.1 Introduction 3.1.1 Coral recruitment studies and coral health sustainability

The measuring of recruitment patterns of marine organisms is of fundamental

importance for understanding the mechanisms that regulate their populations and for

mediating species coexistence (Underwood & Fairweather, 1989). Recruitment is also

recognized as one of the most important factors driving the ecology of marine

invertebrates. In terms of coral reef ecosystems, the recruitment of coral juveniles are

considered a major determinant of community structure in marine ecosystems, and this

has been highly featured in coral reef literature in recent years, where recruitment is

recognized as a fundamentally important influence affecting the distribution and

abundance of organisms (Babcock & Mundy, 1996; Harriot, 1992).

In the midst of declining worldwide coral reefs, conventional coral health monitoring

methods only focus on the current state of coral reefs, with predominant emphasis

placed on measuring the quantity and coverage of corals, along with identifying the

community structure, living forms, and dominant groups of adult corals (Kakaskasen

et al., 2013). It has been acknowledged that these aforementioned methods are

considerably lacking in their capacity to forecast the future health and sustainability of

coral reefs, whereas an assessment of the recruitment of juvenile corals serves to

provide an insight into the viability of young generations of corals in restoring and

promoting the recovery of degraded reef ecosystems.

3.1.2 Coral recruitment assessment methods

There are currently two methods used to assess the recruitment of scleractinian corals.

The first method involves the recruitment of juvenile corals (>1cm) diameter onto that

of natural substrate surfaces, and which is termed “visible” recruitment. The

recruitment of corals at a comparatively earlier and smaller stage is measured using

artificial substrata in the form of settlement plates which can be later removed and


52

microscopically examined; and this is referred to as “invisible” recruitment (Wallace,

1983). It has been acknowledged by Harrison and Wallace (1990), that the recruitment

of juvenile coral spat using the artificial substrate method of removable settlement

plates, is more representative of the availability of coral larvae at the study site as

compared to the observation of visible juvenile corals (> 1cm) onto natural substrata.

This advantage relating to the “invisible” recruitment monitoring method which

involves the sampling of newly settled coral larvae using artificial substrata, takes into

account the minimization of operational influences related to post-settlement processes

such as the effect of post-settlement mortality on the observed coral larvae recruitment

itself (English et al., 1997; Harrison & Wallace, 1990).

3.1.2.1 Artificial substrate used in coral recruitment studies

Coral recruitment studies in the past have previously employed a variety of artificial

substrate surfaces in study sites in order to assess the settlement rates of juvenile coral

spat. Settlement surfaces which have been used include glass, terracotta or ceramic

tiles, PVC surfaces or plastic petri dishes, concrete blocks, tridacnid clam shells, slices

of coral blocks, and the outer surfaces or pieces of dead coral (Harriot & Fisk, 1987).

Unglazed terracotta tiles were selected as the settlement substrate of choice for this

study as it has been previously demonstrated that the use of terracotta tiles was

generally conducive to the recording of higher coral spat settlement densities, when

compared to ceramic tiles. This aspect was reportedly related to the coarse surface

present on terracotta tiles which facilitated the anchorage of settled spat into crevices

present on the tile surface, and thereby minimized dislodgment from the substrate as a

result of depth current action, and predation (English et al., 1997; Vave, 2005).

Previous coral larval studies have also shown a significant increase in genetic diversity

linked with an increase in surface irregularity, with a strong suggestion that a success

in the settlement of rare corals is influenced by the topography of the benthic surface

(Carleton & Sammarco, 1987).

3.1.3 Coral recruitment and its vital role in reef resilience after disturbance

A period of at least 10-20 years are required in order to regenerate coral cover to

original pre-disturbance levels after a disturbance event, whilst entertaining the

assumption that the environment in question is not unremittingly exposed to physical


53

or biological stressors which inhibit or impede coral recruitment i.e. the settlement of

coral larvae, and factors affecting its growth and survival (Coles & Brown, 2007).

Coral recruitment rate is affected by a multitude of factors, some of which include

depth, orientation of the substratum, competition with other organisms, grazing, and

larvae availability as well as dispersal (Banks & Harriot, 1996). The reproductive

capacity of a reef ecosystem is vital to its sustainability, with the viability of its

community structure being largely reliant upon the coral reef communities themselves

being either self-seeding- where the coral larvae can be retained on a reef system

through water flow patterns (Black et al., 1991), or dependent upon the transportation

of larvae from adjacent reefs (Fisk & Harriot, 1990). In this regard, the understanding

of temporal and spatial variations in coral recruitment patterns is considered to be

imperative in attempting to understand the various mechanisms that drive the

resilience of coral reefs after catastrophic disturbances (Salinas-de-Leon et al., 2013).

In a study evaluating the role of recruitment on coral cover change in an impacted reef

system in Hawaii, following that of a major hurricane event, it was found that periodic

pulses in recruitment was the principal determinant responsible for stimulating the

recovery process for the degraded reef system, and also for the re-establishment of

coral cover after the disturbance event (Coles & Brown, 2007). In this situation, it was

found and reported that recruitment was directly linked to sequences of changes in

coral cover observed for two species of Porites corals for a period of between 10-15

years. The integral role of these minor pulses of recruitment which was observed in

this reef recovery scenario, was described by the authors as “important in maintaining

corals that may be marginally surviving on wave impacted reefs in Hawaii and with

relatively low species diversity”

3.1.4 Coral recruitment studies in the Fiji islands and reef resilience

A study conducted in 2008 in the Fiji Islands investigated the variation in coral

recruitment patterns between three sites: the Great Astrolabe Reef, a site in Taveuni,

and with specific significance to this study; a site within the Suva Harbour. The study

recognized that although the Fiji Islands possess one of the largest coral reef systems

in the South-West Pacific, there is very little information or data is available relating

to coral recruitment processes on any of the reefs. The authors emphasized the fact that


54

many of the previously conducted ecological studies dealing with coral reefs in the Fiji

Islands have been limited to species lists, or surveys of bleached corals; with no

previous studies specifically dealing with variation in the coral recruitment rates of

corals in the Fiji Islands having been conducted (Quinn & Kojis, 2008).

In terms of the two survey sites chosen to assess coral recruitment rates in the Suva

Harbour, one was located within the lagoon adjacent to the Suva channel, with this

area designated as “polluted” due to its close proximity to the main shipping port of

Suva City, and on the basis of previous reports verifying the presence of contaminants

in the harbour (Naidu & Morrison, 1994) . This Suva Channel (SC) site recorded the

lowest total overall recruitment rate (51 ± S.D. 29 recruits m 2� yr 1� ), compared to the

highest recruitment rate seen at the Great Astrolabe Reef (YIS) site (1812 ± S.D. 1275

recruits m 2� yr 1� ). It was reported that the second Suva Harbour site (FP), produced

the second highest recruitment rate, with the third site at Taveuni (TA) generating the

third highest recruitment rate.

The authors report that the density of coral recruits at most study sites in Fiji were

comparatively higher than those reported from other tropical sites which had employed

a similar sampling method, however, it was stated that “the only Fijian site with a low

recruitment rate was the turbid water site in the Suva channel” (Quinn & Kojis, 2008).

Although it was found that the Great Astrolabe Reef (YIS) site produced the highest

mean sedimentation rate compared to the other two sites surveyed, and was

periodically subjected to very high sediment loads, it was also unexpectedly

discovered that this same site also produced the highest coral larval recruitment rate

compared to the other two Great Astrolabe Reef (GAR) sites within the same general

vicinity as well (3.5 times greater, with summer recruitment rates at the other two

(GAR) sites being within 10% of each other) (Quinn & Kojis, 2008).

The authors attribute this anomaly of persistent recruitment to the reduced effects of

sedimentation which occurred throughout relatively short periods of rainfall; the

effects of which were dissipated quickly and did not ultimately affect reproduction. In

addition to this, sites found to produce high recruitment were reportedly located on

reefs boasting high coral coverage and fecundity, high species diversity, and a large


55

number of Acroporid broadcast spawning corals; with this coral family producing a

very high abundance frequency of coral larvae in the study. Another interesting

discovery was that the study revealed no evidence of coral bleaching or associated

mortality at the (YIS) site, as it has been documented through literature that highly

turbid environments which produce conditions of low light availability reduce the

depth range of coral species and also bring about coral bleaching and subsequent

mortality (Rogers, 1979). It was also surmised that the conservative mixing of reef

waters within the lagoon, in tandem with the coordinated mass spawning of Acroporid

coral larvae, allowed fertilization success. The retention of coral larvae in this situation

through fertilization, thereby would have generated the high coral recruitment rates

which were observed. This notion, however, was not deemed applicable to the other

two sites within the general area that produced low recruitment rates.

A study by Vave (2005) evaluated the settlement and recruitment of coral larvae in

three different sites around Suva Harbour in the Fiji Islands using various settlement

plate surface types, at varying depths, and during the major and minor coral spawning

season periods specific to the region (Mildner, 1991). The sites located on Suva Reef

included: Fish Patch Reef, Shipwreck, and another selected site located within the

vicinity of the general study site. The findings of the study documented five hundred

and ninety two coral spat which had settled on 288 tiles, and which were deployed

during the aforementioned spawning periods. Coral spat settlement density was

reportedly higher in the shallow depth zone during the major spawning season period

(October-December), and conversely, settlement density was higher in the deep depth

zone during the minor spawning season (March-April). It was determined from this study that coral spat from the genus Acropora were

predominant in the major spawning season, whilst coral spat from the Pocillopora

genus were shown to be more abundant in the minor spawning season; Acropora spat

were also second in abundance for this specific period. Seriatopora spat were stated to

be rare in both spawning periods.


56


Research which was undertaken for this chapter was aimed at testing the following

hypothesis:

i. Coral spat Family diversity and abundance will be significantly higher in the

control site, in comparison to the Dynamite Hut site

The following objective was therefore devised in order to wholly answer the

aforementioned research questions.

i. To determine the coral recruitment rates at the PIS, in comparison with the

base-line site in order to identify resilience and sustainability properties specific to

the PIS.

3.3 Methodology

Techniques and procedures employed in this section of the study were adopted from

English et al. (1997); with applied revisions and modifications to these techniques

based upon guidelines and recommendations from one of the co-supervisors of this

project (Bythell, J, personal communication).

3.3.1 Coral spawning periods in the Fiji Islands

The coral recruitment monitoring period for the “coral spat abundance” aspect of the

study, coincided with the coral mass spawning events previously determined for the

Fiji Islands. On the basis of a study conducted by Mildner (1991) on a Suva Reef site

in Fiji, it was established that the major coral spawning season occurs from early

October to December, with the minor coral spawning season occurring from March to

April; therefore, the occurrence of these two coral spawning events which occur

annually, were reliably predicted 5-6 nights following a full moon, and within the

aforesaid spawning periods determined by Mildner (1991), and adapted by Vave

(2005) (timeanddate.com, 2015). The following table (Table 3.0), outlines the dates

for the full moon phases in the Fiji Islands with respect to the duration of this study,

and the predicted major and minor coral spawning periods thereafter.


57

Table 3.0 Predicted mass spawning events in the Fiji Islands; adapted from (Vave, 2005)

Year 2014 2015

Coral mass spawning Major spawning Minor spawning Full Moon 8th Oct 7th Nov 6th Mar 5th Apr Predicted spawning date 14th Oct 13th Nov 12th Mar 11th April

3.3.2 Seasonality and coral settlement

The Fiji Islands experience a distinct wet season and a dry season. The dry season falls

between the months of May to October, with the wet season typically occurring

between November to April ("The Climate of Fiji," 2006). The monitoring duration

for this study encompasses these two major periods of seasonality, and will attempt to

evaluate the difference in total coral spat density recorded from both study sites, in

both the wet and dry season periods.

3.3.3 Settlement tile preparation

Terracotta tiles used for this chapter were cut to the recommended dimensions of 12cm

× 12cm (English et al., 1997). (Four) tiles were affixed to (one) recruitment station

rack (RSR), with each tile placed adjacent to each other with an allowable spacing of

at least 2.0 cm between each tile. Two tiles were placed adjacent to each other on the

upper portion of the (RSR) working surface, with the remaining two tiles also placed

adjacent to each other and on the bottom-most portion in a general square formation.

Each of the four corners of each terracotta tile was drilled throughout using a tungsten-

carbide tipped 6mm hole-saw bit, and using a bench drill press in order to facilitate the

fastening of each corner to the (RSR) frame using a 200mm plastic cable tie.

Terracotta tiles chosen for this study had corrugations present on the underside of each

tile, and were therefore only uniform in surface area on the upper surface. This was

allowed in order to observe and test the assumption that the planulae larvae of some

coral species show a preference for low-light, cryptic micro-habitats for settlement

(Harriot & Fisk, 1987), and would thereby predominantly settle on this irregular

underside surface.


58

3.3.4 Recruitment Station Rack (RSR)

Recruitment station racks (RSR) were constructed using sections of welded wire mesh

which was bent in the middle of the measured section at a general 90° angle, in order

to allow for a raised oblique angled surface upon which to secure settlement tiles (See

Figure 3.0 (left) and Figure 3.1). Measured sections were specifically sized in order

to accommodate approximately four tiles per rack in a two-by-two square orientation.

Pre-drilled tiles were washed in fresh water to remove debris arising from drilling, and

attached to the rack using 200mm cable ties before deployment. Care was taken to

avoid affixing tiles which were located at the lower portion of the rack, at a position

too close to the substrate, so as to minimize premature fouling of the settlement plates

by re-suspended sediments; hence a 5.0 cm gap was accounted for at the extreme lower

portion of the rack. Tiles were not soaked in seawater prior to deployment, as this was

recommended but not deemed significantly mandatory (English et al., 1997).

3.3.5 Study site Recruitment Station Rack field deployment

The (RSR)’s were individually transported to each allocated deployment area within

each study site and permanently secured onto the substrate with four U-shaped hooks

per (RSR), which were fashioned out of ½” thick construction rebar iron, sharpened at

each driving point, bent at a 180° angle, and secured at each corner of the (RSR). Each

study site had (five) racks, with (one) rack deployed alongside each permanent quadrat

which had been established earlier on in the study. Each (RSR) was placed at a location

earmarked for permanent establishment, and then secured by driving U-shaped hooks

tethering the rack frame, into the substrate using a four pound iron mallet (See Figure

3.0 (right)).

An attempt was made to orient the racks in both study sites in a direction such that the

settlement tile surfaces were facing away from the general direction of the mainland,

and towards the deeper channel area. This was aimed at minimizing sediment-fouling

of the settlement tile surfaces, from sediment influx originating from the direction of

the mainland itself. Each of the numbered racks accompanying its relevant permanent

quadrat station, was linked to subsequent racks by way of a general linear formation,

so as to acquire maximum representation of the selected study area.


59

For both study sites, (RSR) stations were strategically deployed in order to ensure the

placing of (RSR) stations in gradually increasing depth profiles. In this regard, the

(RSR) rack from quadrat 1 (for both sites) was located in the shallowest region, with

successive racks placed in increasingly deeper water until the placement of the (RSR)

from quadrat 5 in the deepest section of the study site.

Figure 3.0 Frontal view of an assembled (RSR): (Left), and an (RSR) being deployed in the PIS by the researcher: (Right)

Figure 3.1 Lateral view of a Recruitment Station Rack


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3.3.6 Study site field data collection

3.3.6.1 Coral Family “abundance” study

Out of the (five) recruitment rack stations deployed within each study site, tiles from

the Quadrat 2 and 4 racks were designated for assessing the “Abundance” aspect of

coral larval families for the duration of the entire study; and were therefore

consecutively collected every two months, as this was the minimum recommended

deployment period allowing for larval settlement, prevention of the over-growth of

algae on settlement tiles, and for minimizing the influence of post-settlement processes

i.e. mortality (English et al., 1997; Harrison & Wallace, 1990; McClanahan, 1997).

Fresh settlement tiles were deployed immediately after the scheduled collection of tiles

under this category of observation using cable ties and cutting pliers.

3.3.6.2 Coral Family “diversity” study

Tiles from racks allocated to Quadrat 1, 3, and 5 in each study site, were designated

for the “Diversity” aspect of the study, and were collected every six months for the

entire duration of the investigation. Fresh settlement tiles were deployed immediately

following collection. Despite the certain influence of post-settlement processes on

settled spat in this context, this procedure was nonetheless undertaken in order to

ascertain the diversity of planulae larvae undergoing settlement and establishment on

a semi-annual timescale in both study sites; an occurrence which would otherwise not

be observable on settlement tiles which were collected every two months under the

abundance aspect of the study. In addition to this, the extended collection duration for

tiles under the “diversity” aspect allowed for the sufficient development of skeletal

features of settled coral spat, and therefore aided in the positive identification of spat

to Family level.

3.3.6.3 Settlement tile retrieval process

Settlement tiles were collected with three specially constructed, labelled, and sectioned

wooden trays in order to minimize damage to settled spat during the transport of

collected tiles to the laboratory (See Figure 3.2). These trays were constructed with

recessed cavities which allowed trays to be stacked one atop of each other without

abrading upon tiles contained within. The trays were marked according to the quadrat

number and the relevant recruitment station where the tiles were retrieved from; with


61

retrieved tiles also marked with the point of a diving knife indicating the number of

the tile from the top left hand corner to the right hand side. Trays were stacked atop of

each other in an open plastic crate, which was also taken underwater in order to aid in

the retrieval process. All tiles were retrieved simultaneously during the retrieval

process. The plastic crate was then taken to the surface and placed in the waiting vessel

before being transported to the laboratory for subsequent processing.

Figure 3.2 Two of the three specially fabricated settlement tile collection trays

3.3.7 Laboratory analysis

3.3.7.1 Settlement tile laboratory conditioning and preparation

Retrieved tiles were washed under a steady stream of fresh water at the Marine Studies

jetty upon arrival from data collection trips, in order to slough off thick mats of

sediment and algae which had covered the surface of the settlement tiles. The relatively

clean tiles were then placed in stainless steel trays which were labelled according to

the quadrat number the tiles had originated from. The trays were then filled with a 10%

bleach solution until the tiles were completely immersed, and then covered and left to

stand for 24 hours in order to remove organic material and reveal distinctive skeletal

features. The bleach solution which was used for this study was comprised of a mixture

of 100mL of CLOROX Concentrated house bleach, which contained 8.25% of Sodium

Hypochlorite, and 900mL of Distilled water.


62

Tiles were then removed from the bleach immersion trays and washed with fresh water

under a faucet, and allowed to dry to ambient temperature before being searched twice

for coral spat in accordance with a protocol developed by Harriot (1992).

3.3.7.2 Dissecting Microscope calibration

An Olympus SZ51 Binocular Microscope was used for observing the presence of coral

spat on recovered tiles, with each tile placed on layers of tissue placed on the stage of

the dissecting microscope in order to prevent damage to coral spat present on the

underside of the tile. Following an initial microscope calibration using a stage

micrometer and eyepiece reticle it was determined that one ocular unit was equivalent

to 26.67 (μm) at an objective of 3X. Calibrations were done at each objective power

and recorded relevant to photographs taken. This allowed for the obtaining of

measurements for each coral spat in micrometers (μm).

3.3.7.3 Coral spat searching and identification

Each visible surface of the tiles were searched for coral spat at the lowest magnification

setting (0.8X) in a “zigzag” manner as demonstrated by Vave (2005), with the aid of

a miniature fluorescent desktop lamp which was used as the primary source of

illumination. Corrugations present on the underside of the tile were intensively

searched up and down the length of each furrow and concavity, and where applicable

a small steel spatula was used to remove calcareous or organic matter in order to

expose the underlying tile surface in an attempt to locate coral spat. Upon discovery

of coral spat, the magnification was then increased to 4X and the coral spat was

identified down to Family level based on the structural features presented by the coral

skeleton.

Identification work conducted in this chapter consisted of classifying coral spat to

Family level, therefore, the measuring of spat corallite diameters was not necessary;

as this is only a requisite when identifying further to genus level. Four coral families

were definitively identified throughout the course of the study, and these were: Family

Acroporidae, Pocilloporidae, Poritidae, and Mussidae. An identification technique

coined by Babcock et al. (2003), and summarized by Vave (2005) was applied here;

where the significant skeletal characteristics of coral spat such as the Coenosteum type,


63

Septa type, and the presence or absence of a Collumelae could be reliably used to

differentiate spat into family classes (See Table 3.1).

Table 3.1 Coral spat identification key for differentiation at Family level using skeletal structural features, adapted from (Vave, 2005) Acroporidae Pocilloporidae Poritidae Mussidae

Coenosteum Porous Solid Solid Solid

Septa Prominent Prominent Septa with teeth Septa exert with numerous irregular spines

Collumellae Absent Present Absent Present (rudimentary)

3.3.7.4 Settlement tile surface area and total coral spat density

The shape of each tile was classified as a right rectangular prism with fixed dimensions

of Length equaling 12cm, Width equaling 12cm, and Height equaling 1cm. The

surface area of each tile was therefore calculated using the formula:

A = 2(wl + hl + hw). Therefore, the surface area for individual tiles used in this study

was found to be 336cm 2 . Total surface area relating to each observation duration in

each study site was therefore calculated in order to make a correlation with total coral

spat density for a fixed area, and during a given period of time.

3.3.7.5 Coral spat characterization

Family Mussidae

Coral spat which are categorised under Family Mussidae have several distinguishing

skeletal structural features which allow them to be classified apart from other family

categories. Family Mussidae have septa which are exert with numerous irregular

spines, a rudimentary collumelae, and the presence of a solid coenosteum (Babcock et

al., 2003). Spat from Family Faviidae e.g. Platygyra sinensis bear similar appearance

to spat from Family Mussidae e.g. Lobophyllia corymbosa, however, upon closer

observation they are separated on the basis of their septal structures. The septal spines

present in Family Mussidae are described as “robust, nodular, and club-like”, and are

set apart from Family Faviidae spat, which have septal spines which have a more

blade-like and saw-toothed appearance aimed above the septal wall (See Figure 3.3).


64

Figure 3.3 Photomicrograph of a Family Mussidae coral spat with visible skeletal structural features

Family Poritidae

Spat from the Family Poritidae also possess a distinguishing skeletal structural feature

which separates them from other coral spat; with this being the presence of prominent

vertical teeth on each of the primary septa (Babcock et al., 2003). Family Poritidae

are also identified through the absence of a columella at the centre region of the spat

which is also a notable feature. In addition to this, coral spat in this family also possess

a solid coenosteum (See Figure 3.4).

Figure 3.4 Photomicrograph of a Family Poritidae coral spat with distinguishing septal teeth clearly visible


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Family Acroporidae

Coral spat from the family Acroporidae also display the distinct lack of a Columella

at the centre of the spat structure, as is also seen in Family Poritidae. This Family is

readily identified through the presence of prominent Septa which is distinctly visible.

The Coenosteum has a porous appearance in this family, and is not solid as is shown

in Families Mussidae and Poritidae (See Figure 3.5).

Figure 3.5 Photomicrograph of a Family Acroporidae spat with prominent septa visible, along with the distinctive lack of a columella.


66

Family Pocilloporidae

Spat categorised under this family demonstrate the presence of a prominent columella;

with this key structural feature allowing this spat to be characterised apart from other

families. There is also the presence of prominent Septal walls in Family

Pocilloporidae, with the Coenosteum structure observed to be solid (See Figure 3.6).

Figure 3.6 Photomicrograph of a Family Pocilloporidae spat with prominent columella clearly visible.


67

Unidentifiable coral spat

Numerous unidentifiable coral spat were encountered from both study sites throughout

the course of the study. These spat specimens could not be accurately identified to

family level due to evident damage to the skeletal structure, or that of insufficient

skeletal development required in order to make a distinctive classification. (Figure

3.7) illustrates a few of these aforesaid unidentifiable spat specimens:

Figure 3.7 Coral spat classified under the “Unidentifiable” category, in what appears to be insufficient skeletal growth for positive identification (Top-Left), damage to skeletal structure (Top-Right), fusion with calcareous matter (Bottom-Left),and insufficient skeletal growth and/or possible damage (Bottom-Right).


68


A total of 242 coral spat were positively identified from both study sites throughout

twelve months of monitoring, and on a combined number of 144 terracotta settlement

tiles. A subtotal of 110 spat were found from the coral spat “Abundance” category,

compared to 132 spat recorded from the “Diversity” category.

Interestingly, the stressor-influenced PIS recorded a relatively high total coral spat

density for the entire duration of the study; which was 106 spat on a surface area of

6720cm 2 from 20 tiles, compared to the control site which revealed the settlement of

132 spat on 6720cm 2 from the same number of tiles.

3.4.1 Coral spat abundance: two month collection intervals

In the coral spat abundance investigation where eight settlement tiles were deployed

and collected every two months in each study site, and for the entire duration of the

study; 110 coral spat were found and identified from both study sites. (See Table 3.2).

Table 3.2 Total coral spat from two month collection intervals; PIS: Dynamite Hut, COS: Dennis’ Patch

Coral spat Family

Coral spat sum in sites COS (Sum) PIS (Sum)

Acroporidae 3 3 Pocilloporidae 31 28

Poritidae 33 12 Mussidae 0 0

Unidentifiable 11 6

The histogram below (Figure 3.8), illustrates the total abundance of coral spat families

found between study sites, after (six) two month collection intervals replicated for a

12 month duration. Coral spat from Family Mussidae were notably absent from this

collection category, as this family was exclusively found in only the six month interval

collection category.


69

Figure 3.8 Coral spat family abundance: two month collection interval

No coral spat was recorded on any settlement tile, in any study site, after the first two

months of monitoring in September 2014 (See Table 3.2). The absence of coral spat

from any settlement tile within both sites, confirmed this period of monitoring to be

that of a “non-spawning” period; as the Major and Minor Spawning periods were

earlier predicted to span from the 14th of October 2014 to the 11th of April 2015.

However, the rationale behind deploying settlement tiles during this period was the

expectation that coral spat from certain species which were “year-round spawner’s”

e.g. Family Poritidae, could be found and identified from tiles collected during this

period.

In month four, 6 Pocilloporidae spat were found in the PIS, compared to 3

Pocilloporidae spat in the COS. The COS also presented with 1 Acroporidae spat in

this period compared to 0 Acroporidae spat found in the PIS. In month six + eight the

COS presented a higher number of coral spat in each of the coral Families compared

to the PIS; with the number of unidentifiable coral spat in the COS for this period

consisting of 4 spat, compared to 1 spat recorded for the PIS. Conversely, in month

ten the PIS presented with a higher number of coral spat in each Family category

compared to the COS; with 2 unidentifiable spat found in the PIS, compared to 3 spat


70

in the COS. In month twelve, no Family Acroporidae, and Poritidae spat were found

in the PIS, however, 10 Family Pocilloporidae spat were found in this site, compared

to 11 for the same Family in the COS. For this period 4 unidentifiable coral spat were

found in the COS compared to 3 in the PIS.

Table 3.3 Coral spat Family two-month interval abundance

*Month 6 and month 8 data collection trips coincided as entry into study sites was prohibited due to the December 06, 2014 sewage spill disaster and Environmental Emergency Declaration.

Coral family abundance: Differences analysis using the Mann-Whitney U test

The Mann Whitney U test was ideal for analysing the data presented in this chapter as

the abundance of coral recruits in Family categories from the two study sites tend to

vary from 0 to any particular value, thus resulting in counts which are not restricted.

Therefore, the Mann-Whitney test is the ideal test which can be applied in this situation

in order to deal with data which is discrete and categorical in nature, and also in order

to find a significant difference in the abundance of coral spat families between sites.

The following null and alternative hypotheses were therefore suggested in order to

investigate the presence of statistically significant differences in coral spat family

abundances between study sites:

Ho: There is no statistically significant difference in coral spat family abundance between the two sites

Ha: There is a statistically significant difference in coral spat family abundance between the two sites

Through the Mann-Whitney U test analysis it was demonstrated that there was a

significant difference in the abundance of Family Poritidae coral spat between the two

study sites (U=605.00, p > 0.022). The null hypothesis was therefore rejected for this

Month

Coral spat Family, Site, and Abundance (Sum) Acroporidae Pocilloporidae Poritidae Mussidae Unidentifiable PIS COS PIS COS PIS COS PIS COS PIS COS

2 0 0 0 0 0 0 0 0 0 0 4 0 1 6 3 0 0 0 0 0 0

6+8* 0 1 5 12 1 19 0 0 1 4 10 3 1 7 5 11 8 0 0 2 3 12 0 0 10 11 0 6 0 0 3 4


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coral spat Family. Looking at the mean ranks in the below table (See Table 3.4), it can

be learned that the COS presented a higher abundance of Family Poritidae, in

comparison to the PIS. This result was expected as a larger diversity and abundance of

Porites species were observed in the COS during the coral cover analysis described in

Chapter two.

For all other coral spat Families there was no significant difference in coral spat

recruitment between sites (p-value > 0.05), which means that there is insufficient

evidence in the data to reject the null hypothesis. In terms of Family Acroporidae it

can be seen that there is absolutely no significant difference in terms of coral spat

family abundance between the two study sites (U=800.0, p < 1.000). Family

Pocilloporidae also presents with no significant difference in abundance between the

two study sites (U=764.5, p < 0.706). With regards to the Unidentifiable category there

is also no significant difference seen in terms of the number of unidentifiable coral

spat found between the two study sites (U=734.0, p < 0.349).


3.4.1.1 Coral spat density and coral spawning

After interpreting the percentages of coral spat from the total sum which was found

and identified after the completion of monitoring, it was generally found that more

coral spat from all family categories, and for both study sites, were found and identified

during the spawning seasons (SS) - Major Spawning Season: 14th October to 13th

November, and Minor Spawning Season 12th March to 11th April, in comparison to the

non-spawning season (NSS) (See Table 3.5). The percentage of coral spat for both

sites during the spawning season (SS) was found to be 65%, with the percentage of

coral spat for both sites and during the non-spawning season (NSS) being only 35%.

Coral spat Family

Significance value

Mann-Whitney U Mean Rank PIS COS

Acroporidae 1.000 800.000 40.50 40.50 Pocilloporidae 0.706 764.500 39.61 41.39 Poritidae 0.022 605.000 35.63 45.38 Unidentifiable 0.349 734.000 38.85 42.15


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Table 3.5 Sum of coral spat found in differing spawning seasons

3.4.1.2 Coral spat abundance in Wet and Dry seasons

Based on a Fiji Meteorological service information sheet release, the Fiji Islands

experiences a distinct dry Season from May-October, and a distinct wet season from

November-April ("The Climate of Fiji," 2006). A shoulder season is reported to exist

between the seasons and falls within the period (May-June).

Coral spat abundance from both sites were found to be the most highest during the dry

Season (n=74), with a contrastingly lower spat number recorded for the wet Season

(n=53) (See Table 3.6). In terms of the effect of seasonality on coral spat abundance

in each study site, the PIS recorded the highest coral spat settlement density during the

dry season (n=36), and (n=13) for the wet season. Conversely, however, the COS

recorded a marginally higher coral spat settlement density during the wet season (n=

40), and (n=38) for the dry season.


The Pearson’s Chi Squared test was then performed in order to investigate the possible

presence of statistically significant associations between coral spat family abundances

found in both study sites and seasonality. The following hypotheses were therefore

formulated in order to test the aforesaid assumption:

Acroporidae Pocilloporidae Poritidae Unid

Site

PIS

Spawning Season

NSS 0 10 0 3 SS 3 18 12 3

Total 3 28 12 6

COS Spawning

Season NSS 0 11 6 4 SS 3 20 27 7

Total 3 31 33 11

Coral spat

Family

Site, Season, coral spat sum Dry Wet

PIS COS PIS COS Acroporidae 3 1 0 2

Pocilloporidae 17 16 11 15 Poritidae 11 14 1 19

Unidentifiable 5 7 1 4 Total 36 38 13 40


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Ho: There is no statistically significant association between coral spat family

abundance in both study sites and seasonality

Ha: There is a statistically significant association between coral spat family

abundance in both study sites and seasonality

No significant association (p-value > 0.05) between any particular coral spat family

and season was found after performing the Pearson’s Chi Squared test. The null

hypothesis was therefore accepted. However, based on coral spat counts observed

from generated cross-tables, it was learned that Family Acroporidae spat recorded

slightly higher counts in the dry season compared to the wet season, along with

correspondingly lower 0 coral spat counts in the dry season compared to the wet

season. Family Pocilloporidae also recorded insignificantly higher spat counts in the

dry season compared to the wet season, however, there was a higher number of 0 spat

counts seen in the dry season in comparison to the wet season for this coral family. For

Family Poritidae there were also slightly higher spat counts in the dry season

compared to the wet season, with higher 0 coral spat counts found in the dry season

compared to the wet season also. For the unidentified coral spat category, high coral

spat counts were observed in the dry season compared to the wet season. A higher

number of 0 coral spat counts were also observed for the dry season compared to the

wet season for this unidentified category (See Table 3.7).

Table 3.7 Pearson’s Chi Squared test results for coral spat abundance in alternate seasons

3.4.1.3 Zero coral spat count prospective cohort study

Pollution and resultant water contamination is a significant and documented factor at

the PIS which is located within Suva Harbour (Naidu & Morrison, 1994). This limiting

variable was projected to have an impact on the existence of coral spat families in this

site, therefore, it was assumed that the presence of a “0 coral spat count” would indicate

Coral spat Family

Pearson Chi Square

value

Significance value

Season and Spat Count

WET DRY Acroporidae 0.120 0.729 2 4 Pocilloporidae 0.890 0.828 15 22 Poritidae 6.275 0.280 8 17 Unidentified 1.410 0.494 5 10


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the lack of coral recruitment in this site and support this notion of impaired

sustainability. A Prospective Cohort Study was then undertaken in order to investigate

the relative risk of a particular site in having a zero coral spat count.

It was found that for Family Acroporidae a non-significant likelihood (p-value > 0.05),

of one site having a higher 0 coral spat count than the other site existed. There was an

equal likelihood of a 0 coral spat count occurring in the PIS (risk estimate: 1.000), as

well as in the COS (risk estimate: 1.000). For Family Poritidae a significant likelihood

(p-value < 0.05) of a 0 coral spat count occurring in the PIS existed (risk estimate:

1.818), in comparison to a lesser likelihood of this occurrence for the COS (risk

estimate: 0.615). Family Pocilloporidae also recorded an insignificant likelihood (p-

value > 0.05), of one particular site having a greater 0 coral spat count in comparison

to the other site. For this coral Family the PIS presented with a higher risk estimate of

1.107, with the COS having a risk estimate of 0.904 (See table 3.8).


3.4.2 Coral spat diversity: six month collection intervals

In the coral spat diversity investigation where twelve settlement tiles were deployed

and collected every six months, and in each study site, for the entire duration of the

study; 132 coral spat were found and identified from both study sites (See Table 3.9).

Table 3.9 Total coral spat from six month collection intervals

Coral Family

Coral spat sum in sites COS (Sum) PIS (Sum)

Acroporidae 28 9 Pocilloporidae 25 31

Poritidae 11 20 Mussidae 5 3

Unidentifiable 14 24 Total 83 87

Coral spat Family

Pearson Chi Square

value

Sig. value

0 count (spat sum)

>1 count (spat sum)

Risk estimate

PIS COS PIS COS PIS COS Acroporidae 0.000 1.000 3 3 37 37 1.000 1.000 Pocilloporidae 0.202 0.653 23 21 17 19 1.107 0.904 Poritidae 4.713 0.030 32 23 8 17 1.818 0.615


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The histogram below (Figure 3.9), illustrates the total abundance of coral spat families

found between study sites, after (two) six month collection intervals replicated for a

12 months duration. Coral spat from Family Mussidae were present in this collection

category, as this Family was exclusively found in only the six month interval study

category.

Figure 3.9 Coral spat family abundance: six month collection intervals

The PIS recorded a slightly higher total coral spat count (n= 87), in comparison to the

COS (n= 83) after the completion of twelve months of monitoring (See Table 3.9). In

this aspect of the study, the coral spat Family Mussidae was present in both sites,

however, a slightly higher abundance of this Family was observed in the COS

compared to the PIS.

In comparison with the two-month collection interval study, both sites individually

presented with higher total abundances of Family Acroporidae. Similar abundances of

Family Pocilloporidae were also seen in both sites compared to the former study. The

PIS saw a large increase in Family Poritidae spat in this study aspect, with the COS

seeing a converse decline in the abundance of this coral spat Family; compared to a

previous high abundance trend observed in the two month collection interval. A higher


76

number of Unidentifiable coral spat were also noted for both study sites in this six-

month interval aspect, compared to the former.

The first collection of settlement tiles for this category had to be undertaken in month

eight due to restricted access into study sites within Suva Harbour as a result of the

December 06, 2014 sewage spill disaster. In month eight the COS recorded a relatively

large abundance of Acroporidae spat (n= 27), in comparison to the PIS (n= 8). The

COS also recorded a slightly higher abundance of Pocilloporidae spat (n=16),

compared to the PIS for this same collection period (n= 11). A marginally higher

abundance of Family Poritidae was seen in the PIS (n= 6), compared to the COS (n=

3). For Family Mussidae, zero spat were found in the PIS, whereas (n=5) spat from

this coral Family were found in the COS. Similar Unidentified spat numbers were seen

in both sites for this collection period (See Table 3.10).

In month twelve, both study sites recorded similarly low Acroporidae spat abundances.

For Family Pocilloporidae the PIS recorded a relatively high abundance (n= 20), in

comparison to a low spat count for the COS (n= 9). For Family Poritidae the PIS once

again recorded a relatively higher coral spat abundance (n= 14), compared to the COS

(n= 8). For Family Mussidae (n=3) coral spat were found in the PIS, compared to zero

spat found in the COS. A relatively high number of Unidentifiable coral spat were

found in the PIS (n= 14) for this study aspect, compared to (n= 3) spat for the COS.

Table 3.10 Coral spat Family six-month interval abundance

*Data collection was conducted in month 8 as opposed to month 6 as entry into study sites was prohibited due to the December 06, 2014 sewage spill disaster and Environmental Emergency Declaration

Month

Coral spat Family, Site, and Abundance (Sum) Acroporidae Pocilloporidae Poritidae Mussidae Unidentifiable PIS COS PIS COS PIS COS PIS COS PIS COS

8* 8 27 11 16 6 3 0 5 10 11 12 1 1 20 9 14 8 3 0 14 3


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Coral family diversity: Analysis using the Mann-Whitney U test

The aforementioned null and alternative hypotheses which were previously suggested

for the two-month collection interval study, will also be applicable here for the six-

month collection interval study; in order to investigate the presence of statistically

significant differences in coral spat family abundances between study sites.

Looking at the asymptotic significances in the below table (See Table 3.11) after

performing the Mann-Whitney U test, it can be inferred that there is no statistically

significant difference in the abundance of any particular coral spat Family category

between study sites (p-value > 0.05). Therefore there is insufficient evidence in the

dataset to reject the null hypothesis with respect to all coral spat family categories.


Based on the respective coral spat family abundance mean ranks in each site (See

Table 3.11), it can be learned that the COS study site presented a slightly higher

(statistically insignificant) abundance of Family Acroporidae and Mussidae coral spat,

compared to the PIS over a 12 month period. For Family Pocilloporidae and Poritidae

coral spat, the PIS also presented a slightly higher (statistically insignificant)

abundance of coral spat in each Family category compared to the COS. In terms of the

Unidentifiable spat category, the PIS again presented with a slightly higher abundance

mean rank value compared to the COS.

3.4.2.1 Coral spat abundance in Wet and Dry seasons

Coral spat abundance from the six-month interval study was found to be most abundant

throughout the wet season (n= 97), compared to the abundance of coral spat discovered

and identified in the dry season (n= 73). In terms of the effect of seasonality on coral

spat abundance in each study site, the PIS recorded the highest coral spat settlement

density during the dry season (n=52), and (n=21) for the wet season. The COS also

Coral spat Family

Significance value


Acroporidae 0.121 225.000 21.88 27.13 Pocilloporidae 0.688 269.500 25.27 23.73 Poritidae 0.259 240.000 26.50 22.50 Mussidae 0.649 274.500 23.94 25.06 Unidentifiable 0.184 229.000 26.96 22.04


78

recorded its highest coral spat settlement density during the dry season (n= 62), and

(n=35) for the dry season (See Table 3.12).


Similar to the two-month collection interval study, a Pearson’s Chi Squared test was

again performed for the six-month interval study in order to investigate the possible

presence of statistically significant associations between coral spat family abundances

found in both study sites and seasonality. The aforesaid hypotheses relevant to this test

in the previous two-month interval category was also applicable here.

Contrary to the two-month interval study, a statistically significant association (p >

0.011) between Family Acroporidae and seasonality existed (See Table 3.13). Based

on coral spat counts observed from generated cross-tables it was ascertained that

Family Acroporidae spat were more predominant in the wet season, compared to the

dry season. This was correlated with a higher number of 0 coral spat counts which

were seen for the dry season (n= 22), compared to (n= 10) for the wet season.

For the rest of the coral Families, no significant association (p-value > 0.05) between

any particular coral spat family found in both sites, and season, was found after

performing the Pearson’s Chi Squared test. For Family Pocilloporidae, it was observed

from cross-tables that an insignificantly higher number of coral spat counts were

recorded in the dry season (n= 16), compared to the wet season (n= 12); with a

correspondingly higher number of 0 coral spat counts (n= 12) observed for the wet

season, compared to (n= 8) for the dry season also. For Family Poritidae it was also

observed that an insignificantly higher number of coral spat were present in the dry

season (n= 11), compared to (n= 8) for the wet season; with lower 0 coral spat counts

also seen in the dry season (n= 13), compared to the wet season (n= 16). In Family

Coral spat

Family

Site, Season, coral spat sum Dry Wet

PIS COS PIS COS Acroporidae 1 1 8 27

Pocilloporidae 20 9 11 16 Poritidae 14 8 6 3 Mussidae 3 0 0 5

Unidentifiable 14 3 10 11


79

Mussidae, the coral spat counts seen in both seasons deviated slightly from each other

with (n= 4) coral spat recorded in the wet season, and (n= 3) spat found in the dry

season. The number of 0 coral spat counts in each season were also similar with (n=

20) for the wet season, and (n= 21) for the dry season.

Table 3.13 Pearson’s Chi Squared test results for coral spat abundance in alternate seasons

3.4.2.2 Zero coral spat count prospective cohort study

A prospective cohort study was also performed for the six-month interval study in

order to investigate the relative risk of a particular site in having a zero coral spat count.

For Family Acroporidae in the six-month interval study, no significant likelihood (p-

value > 0.05), of one site having a higher 0 coral spat count than the other site existed.

There was, however, an insignificantly higher likelihood of a 0 coral spat count for

Family Acroporidae occurring in the PIS (risk estimate: 1.500), compared to a lower

risk estimate for the COS (risk estimate: 0.700). For Family Pocilloporidae there was

absolutely no likelihood (p-value= 1.000), of one site having a higher 0 coral spat count

than the other site. There was an equal risk estimate value (risk estimate 1.000)

generated for both study sites with respect to this coral family.

With regards to Family Poritidae, no significant likelihood (p-value > 0.05), of one

site having a higher 0 coral spat count than the other site existed. For this coral Family,

however, the COS surprisingly presented with a greater risk (risk estimate: 1.310), of

having a higher 0 coral spat count than the PIS (risk estimate: 0.774). Family Mussidae

also presented with no significant likelihood (p-value > 0.05), of one site having a

higher 0 coral spat count than the other site. For this coral Family, the PIS presented

with a greater risk (risk estimate: 1.195), of having a higher 0 coral spat count than the

COS (risk estimate: 0.854) (See Table 3.14).

Coral spat Family

Pearson Chi Square

value

Significance value

Season and Spat Count

WET DRY Acroporidae 14.786 0.011 14 2 Pocilloporidae 3.018 0.555 12 16 Poritidae 7.577 0.056 8 11 Mussidae 1.024 0.599 4 3


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3.5 Conclusion

3.5.1 Recruitment between sites

In conclusion, the data obtained in this study does not support the hypothesis that coral

spat Family diversity and abundance will be significantly higher in the COS, in

comparison to the PIS, as the latter exhibited remarkably noteworthy coral recruitment

rates in comparison to the offshore control site. In terms of a total annual yield of coral

spat from within both study sites, the PIS displayed an abundance of coral spat and

level of recruitment which was observed to be on the same level as that of the offshore

site; which was not directly impacted by a high magnitude of anthropogenic stressors.

This finding could form the basis of the assumption that the high level of recruitment

seen in the PIS, is one of the more important factors influencing the persistence and

resilience of the relic reef ecosystem observed in this particular area; made possible

through the seeding of coral larvae from nearby coral reef ecosystems i.e. Fish Patch

Reef, and by way of favourable current patterns in Suva Harbour diverting coral larvae

into this location.

3.5.2 Coral spat abundance between sites (Six-month study)

In the six-month interval (long term) recruitment study, an interesting finding revealed

the presence of no statistically significant difference in the abundance of any particular

coral spat Family category between study sites. This discovery highlights the resilience

capacity of the PIS reef ecosystem in terms of a clear persistence in a sub-optimal

environment, amidst varying magnitudes of stressor variables. A clear demonstration

of coral post-settlement survival is evident here as well, as coral spat in latter growth

stages were observed on settlement tiles retrieved from the PIS. This survivability may

be explained through the possibility of coral larvae using the PIS as refugia from heat

Coral spat Family

Pearson Chi Square

value

Sig. value

0 count (spat sum)

>1 count (spat sum)

Risk estimate

PIS COS PIS COS PIS COS Acroporidae 1.500 0.221 18 14 6 10 1.500 0.700 Pocilloporidae 0.000 1.000 10 10 14 14 1.000 1.000 Poritidae 0.784 0.376 13 16 11 8 0.774 1.310 Mussidae 0.167 0.683 21 20 3 4 1.195 0.854


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and light stress; as Chapter Four of this study describes inherent low light and turbid

conditions observed and recorded in the PIS throughout monitoring intervals.

In general the number of coral spat found on settlement tiles deployed in the six-month

interval study for both sites was found to be more predominant in the wet season in

comparison to the number of spat found from both sites in the dry season. In terms of

individual site abundance, however, the PIS recorded higher spat numbers in the dry

season, with the COS also recording higher dry season spat abundance.

3.5.3 Coral spat abundance between sites (Two-month study)

In the two-month study the total abundance of coral spat Families was again found to

be similar between both study sites; except for Family Poritidae which was found to

be significantly higher in abundance in the COS. This interesting finding serves to

consolidate the notion that the stressed inshore site does demonstrate a noteworthy

resilience capacity; and that of which serves as a testament to its persistent

sustainability.

For the two-month interval monitoring study, however, in general coral spat for both

sites were more predominant in the dry season in comparison to the wet season. With

regards to individual site abundance, the PIS recorded higher spat counts in the dry

season, with the COS having more spat abundance in the wet season for this category.

3.5.3.1 Coral spat and spawning seasons (Two-month study)

The predicted spawning dates proposed in the methodology section of this chapter

were confirmed by the finding which reported a higher abundance of coral spat which

were collected and identified in the spawning season (Major Spawning Season: 14th

October to 13th November, and Minor Spawning Season 12th March to 11th April), as

opposed to the non-spawning season. It can therefore be suggested that on the basis of

this study, the coral spawning dates for the Fiji Islands as suggested by Mildner (1991)

are an accurate and reliable measure of coral spawning periods.

3.5.4 Relative risk estimate for coral spat presence between sites

A reliable rate of recruitment conducive to reef sustainability was observed in the PIS

study area. However, on the basis of results obtained from a prospective cohort study


82

performed on data obtained in both monitoring study intervals, it was observed that

notwithstanding the high level of recruitment seen in this site, that there is still a

statistically high risk of obtaining zero coral spat abundance in the PIS compared to

considerably lower risk estimates obtained for the COS. This finding serves to

highlight the tenuous nature of the PIS reef ecosystem, and questions the sustainability

of this site whilst persisting through multiple inshore disturbances (See Appendix 1.3).

Ronal Lal CHAPTER FOUR

83

CHAPTER FOUR

DETERMINATION OF LONG-TERM SEDIMENTATION RATES IN VIEW

OF IDENTIFYING THE MAGNITUDE OF THIS STRESSOR INFLUENCE

ON CORAL HEALTH

4.1 Introduction 4.1.1 The use of sediment traps in coral reef health monitoring

Sediment traps are referred to as “standard tools” for monitoring sedimentation rates

in coral reef environments. They are defined as “containers deployed in the water

column for the purpose of a) acquiring a representative sample of the material settling

vertically through the water column, and b) providing an integrated particle collection

rate and particle properties over the time of deployment” (Field et al., 2011). Sediment

traps have been used to assess the levels of sedimentation in hermatypic coral reef

environments since the 1970’s, and are still favoured as a reliable environmental

monitoring tool due to their relatively simple design and construction, and their

application in a wide variety of uses. Sediment traps are also recommended as reliable

and cost-effective environmental monitoring tools in order to determine the influence

or efficacy of land-use practices on surrounding ecosystems.

4.1.2 Coral reef sedimentation in Fiji: Past evaluations

There is evidence that coral reef deterioration observed in the Fiji Islands was found

to be ascribed to voluminous overland runoffs of terrigenous material from agricultural

practises (Dadhich & Nadaoka, 2012). This was primarily due to the expansion of

croplands and the conversion of forestlands for the purpose of agriculture, which

brings about the consequent erosion and transport of fine sediments and nutrients into

near shore reef areas. It is also reported that dissolved heavy metals and numerous

other toxic substances adhere to fine-grained terrestrial sediment and are then

transported as overland runoff within the near shore reef ecosystem (Dickson et al.,

1987)

The removal of mangroves from coastal regions further exacerbates this situation

through increased sediment deposition, and produces turbid conditions which reduce

water transparency as a result of sediments remaining in suspension. Coral health is


84

resultantly affected by these turbid conditions through the limited amount of light

available for photosynthetic organisms residing in coral i.e. zooxanthellae.

This situation is further compounded by the continuous resuspension of sediments

through wind driven wave action; which bring about large fluctuations in turbidity (0-

>100 mg/l) (Browne, 2012). Nutrients which are carried into inshore reef areas in

suspension, also serve to stimulate macro-algal proliferation, which can also directly

kill corals, trap sediments, inhibit and prevent coral settlement, and also dominate

benthic space (McClanahan et al., 2012).

4.1.3 Impairment of coral fertility through high sedimentation

Sedimentation in coral reef environments has been known to significantly affect the

survivability and sustainability of scleractinian corals by impairing and affecting

growth and calcification processes, reproduction, respiration, feeding and

photosynthesis, fecundity, community structure, and larval settlement onto substrate

(Salinas-de-Leon et al., 2013). Suspended sediments which cause turbidity is the

portion of sediment which is transported by fluid flow and settles at a very slow rate

seldom touching the bed. It is primarily composed of clay, silt, fine sand, and is

maintained in suspension by the velocity and turbulence of flowing water. In the

findings of a related study concerning laboratory trials investigating the effects of

various types of suspended sediments, inorganic nutrients and salinity on that of coral

fertilisation rates and embryo development; it was revealed that an increase in

sedimentation rate had a directly adverse effect on that of fertilisation rates. It showed

that fertilisation rates displayed a marked decrease in correlation with increasing

sedimentation rates as well as a decline in salinity levels. It was also incredulously

noted that the fertilisation rates of corals were reduced by more than 50% when

suspended sediments of 100mgL 1� and a salinity concentration of 30 parts-per-

thousand was simulated in trials (Humphrey et al., 2008). Furthermore; there was a

prevalence of development stage abnormalities in 100% of embryos and no

fertilisation at a salinity concentration of 28 parts-per-thousand. This finding is also

consolidated by Gilmour (1999) who found that suspended sediments of 50-100 mg L1� substantially reduced larvae survivability and settlement; along with significantly

reduced fertilisation rates in Acropora digitifera reef building coral.


85

4.1.4 Coral persistence in high sedimentation environments

However, a study conducted at a site in Yanuyanu-i-Sau at the Great Astrolabe Reef

south of Viti-Levu, Fiji revealed that high sedimentation rates in that area did not result

in low coral recruitment rates. (Quinn & Kojis, 2008). Typically, it is acknowledged

that sedimentation significantly reduces the potential reproductive capacity of corals

(Kojis & Quinn, 1984), however in this particular study site it was unexpected that

such a high coral recruitment rate was generated in the site with the highest

sedimentation rate.

Moreover, an extensive study conducted in the Great Barrier Reef area in Australia

found that high coral growth was observed at a designated Middle Reef area which

experienced turbid conditions. This study disputes previous reports stating that corals

living in turbid waters exhibit slower growth rates compared to corals growing on clear

water reefs due to an onset of increased sedimentation through land-use changes and

resultant coastal runoff which reduce water quality and limit light availability (Couce

et al., 2012).

The corals on Middle Reef were reported as having adapted to their marginal growth

conditions, high sediment loads and reduced water quality; whereby, they displayed

temporally stable growth rates regardless of continuous coastal development in the

area throughout the last 30 years (Browne, 2012). In support of this, the adaptation of

coral species to various levels of short-term exposure to sedimentation in the

Caribbean has also been reported by Rogers (1983). Similarly, Fabricius (2011), also

states that adult corals are able to persist in eutrophic environments with high

sedimentation rates due to the fact that they are able to tolerate prolonged periods of

low light and also have the ability to compete with macro algal populations which have

arisen as a result of nutrient enrichment of their habitat. It is further elucidated that

hard corals demonstrate their resilience through their capacity to occupy several

trophic levels and from their uptake of dissolved organic and inorganic nutrients in

eutrophic conditions.

In environments experiencing excessive sedimentation loads the coral organism has to

expend additional energy in order to slough off sediment particles, which can also

cause the death of entire coral colonies which become buried through excessive


86

sediment deposition (Rogers, 1990). In spite of this, studies have shown that even

though the burial of corals usually leads to their mortality after a certain number of

hours, certain species have been found to be capable of withstanding applications of

large amounts of sediments in a laboratory setting (Hubbard & Pocock, 1972; Lasker,

1980), as well as in the field environment itself (Lasker, 1980; Rogers, 1983).

Sedimentation also adversely affects the future sustainability of the reef ecosystem by

eliminating the presence of viable hard substrate required by juvenile coral recruits for

settlement, as well as reducing the fecundity of corals at depth (Kojis & Quinn, 1984;

Rogers, 1990).

4.1.5 Coral physiological response to high sedimentation

The mechanisms that corals employ to withstand and persist in high sediment-influx

environments include the use of their tentacles and cilia, stomodeal distension through

the uptake of water, and the entanglement of particles in mucous which later sloughs

off the coral colony surface (Hubbard & Pocock, 1972; Rogers, 1990). Certain coral

species also tend to differ in their ability to inhibit sediment coverage, and this attribute

directly pertains to the general morphology of the coral colony and the coral calyx

structure. In this regard, it was found in a study that colonies of Agaricia agaricites

adapted to sedimentation stress through a shift in the coral colony orientation and also

through changes in its morphological characteristics (Bak & Elgershuizen, 1976).

Moreover, Logan (1988) attributes the frequently observed orientation of the large

calyx in Scolymia cubensis which projects at a steep angle from the horizontal plane,

to be an adaptive mechanism exhibited by the species in order to allow for efficient

sediment removal.

4.1.6 Coral compensatory response in light deprived environments

Fabricius (2011), also acknowledges that most hard coral species have the potential to

adapt to variations in light intensity as well as food availability in a matter of days.

The survivability of hard coral species are also remarkable, whereby it is known that

whilst high levels of inorganic nitrogen as well as phosphorus bring about noteworthy

changes in the physiology of corals; they do not induce mortality or generate

significant harm to the individual coral colonies themselves. Hard corals utilise

particulate organic matter (POM) in order to compensate for energy lost through lack

of photosynthetic activity in light deprived and turbid conditions, and also harness


87

POM for tissue thickness provisions, photosynthetic pigment concentrations, and in

order to stimulate calcification for growth and development. In this regard,

Chromophoric Dissolved Organic Matter (CDOM) which is the light absorbing

fraction of dissolved organic carbon in the water column (Rochelle-Newall & Fisher,

2002), was shown to lower coral mortality due to bleaching in severely turbid waters

in the Gulf of Kutch, Sri Lanka, whereby, this dissolved organic matter has shown to

absorb UV radiation considerably more strongly than particulates such as detritus and

phytoplankton, along with that of visible radiation. This holds great significance for

managing UV penetration in near-shore reef areas (Jokiel & Brown, 2004).

Evidence of near-shore coral reef resilience is also supported by observations showing

that inshore temperature conditions present on that of shallow coral reefs differ greatly

from temperatures observed off-shore. This is reportedly attributed to increased

turbidity as a result of close proximity to landmasses and greater cloud cover; factors

which markedly reduce irradiance and the potential for bleaching. Bays, lagoons and

estuaries are spared from an increase in sea surface temperature due to intervening

factors of land mass, influence of inshore topography on wave action, and changes in

wind conditions and currents in near-shore reef habitats.


The following hypothesis was formulated in order to encompass the nature of research

to be conducted in this chapter.

i. Sedimentation and Particulate Organic Matter content in sediment will be

significantly higher in the Dynamite Hut site in comparison to the control site.

The following objective was devised in order to test the aforementioned hypothesis:

i. To monitor and identify the sedimentation rate at the (PIS) and at the control

site as part of a general coral health timeline in order to compare and contrast coral

health and growth characteristics.


88

4.3 Methodology

The following sections indicate the various types of equipment, field techniques, and

laboratory procedures that were employed in the attempt to determine sedimentation

rate at both of the designated study sites. The methodology applicable to this chapter

was developed under the guidance of the co-supervisor of this study (Bythell, J,

(personal communication).

4.3.1 Sediment trap construction

Sediment traps used for field data collection in each of the two study sites were

constructed according to guidelines recommended in English et al. (1997). (One)

sediment trap was deployed alongside each of the (five) Permanent Quadrats in each

of the two study sites. Each sediment trap was comprised of (three) PVC pipe traps

placed exactly adjacent to each other, with sealed bases, and affixed with cable ties

onto a rebar construction rod which was 0.5 inches in diameter and 1.50 meters in

length (See Fig. 4.0). Each PVC trap was 5 centimeters in diameter, and cut to 11.5

centimeters in length. The use of baffles placed at the mouth of sediment traps prevent

the intrusion of fish and invertebrates, and the subsequent disruption of settled

sediment matter, however, no baffles were placed at the mouth of PVC traps used in

this study as it was found that the use of baffles may result in the decreased trapping

efficiency of sediment traps (Knauer & Asper, 1989). The base of each PVC trap was

sealed using a specifically adapting PVC pipe cap, and PVC cementing solution was

used for ensuring permanent adhesion.


89

Figure 4.0 Recommended sediment trap design extrapolated from (English, et al., 1997): (Left), and constructed sediment trap: (Right).

4.3.2 Study site field deployment

In accordance with recommendations from English, et al. (1997), each sediment trap

was positioned exactly 20 centimetres above the substratum in each of the study sites.

Each rebar construction rod forming the frame of the sediment trap proper, was clearly

marked at the correct position extending from the top most section in order to verify

correct insertion and allowance of this predetermined measurement. The bottom

section of the rebar was cut at an oblique angle in order to produce a sharp point and

allow ease of insertion into the substrate itself. The rebar rod was then hammered at a

90 degree angle directly into the substrate until such a position at where upon placing

the PVC traps on the rod, the traps were positioned at exactly 20 centimetres above

the substrate, and such that the top most point of the rebar was not protruding above

the top level of the secured PVC traps (See Fig. 3.7).


90

Figure 4.1 Sediment trap shown in situ at the PIS

4.3.3 Study site field data collection

(Five) sediment traps were established in each study site, and were collected once

every month from the date of establishment for the period of (twelve) months using

SCUBA apparatus. Prior to the retrieval of each PVC trap, each of the traps was capped

off with a specifically adapting PVC pipe cap. A thick rubber band was then stretched

across the longitudinal length of each trap in order to prevent inadvertent cap removal

and sediment sample loss in the retrieval process. The two cable ties securing each

individual trap to the rebar iron were then cut with cutting pliers, and each of the

capped and secured traps were then placed in a zip-lock plastic bag labelled according

to the quadrat from where it was retrieved, and each of the bags in turn placed in a

large hard plastic container (See Fig. 4.2).

Figure 4.2 Sediment traps prepared for retrieval: (Left), and retrieved traps ready for weight and composition analysis: (Right)


91

4.3.4 Monthly consecutive deployment

Fresh PVC traps were deployed following the scheduled retrieval of traps in both

study sites. Clean and empty PVC traps were taken to the sediment trap stations in

the hard plastic retrieval container and systematically replaced with full PVC traps

using two cable ties per PVC trap (See Fig. 4.3).

Figure 4.3 Securing of fresh PVC traps

4.3.5 Laboratory analysis

Following retrieval from the study site, each PVC trap was then de-capped, and the

contents carefully transferred directly into clean and labelled 50mL Eppendorf

centrifuge tubes using a clean metal spatula. Depending upon the quantity of sediment

received at any given collection interval, the contents of each PVC trap were

sometimes distributed amongst several labelled 50mL Eppendorf centrifuge tubes for

centrifuging and subsequently combined for the latter part of the analysis. The

centrifuge tubes were individually labelled according to the quadrat from which the

PVC trap contents were retrieved from, along with the PVC trap number i.e. 1, 2 or 3.

Distilled water was used to aid in the removal of the sediment sample from the PVC

trap, and also to fill each tube up to the 50 mL mark. Algal growth and encrusting

matter found along the inside of each trap was not collected for analysis, however,

distilled water was used to thoroughly flush and retrieve any ensnared sediment matter

from these growths. This was done in order to ensure unbiased results pertaining to

particulate organic matter content (POM).


92

Each tube was then centrifuged for 10 minutes at 4500 revolutions-per-minute and at

26 degrees Celsius in a (Thermo IEC Centra CL3R) Refrigerated Centrifuge.

Following this, the supernatant was then poured off and the centrifuge tube was then

filled to the 30mL mark with distilled water. The tube was then shaken to stir the

contents, and then re-centrifuged at 4500 RPM for 10 minutes. This was done in order

to ensure the removal of salts from the remaining sediment pellet.

After centrifuging, the supernatant was again poured off from each centrifuge tube,

and the sediment pellet was then transferred to a pre-conditioned, pre-weighed, and

labelled Crucible. A spatula along with distilled water was used to remove the

sediment pellet from the centrifuge tube and into the prepared crucible.

Crucibles used in this analysis section; were conditioned by placing them in a (Ceramic

Engineering OELMEC) Muffle Furnace for 4 hours at 450 degrees Celsius. The

crucibles were labelled prior to conditioning according to quadrat number and PVC

trap number. The crucibles were removed from the Muffle Furnace and placed

immediately in a desiccator with fresh silica gel for 30-40 minutes for cooling. The

initial weight of individual crucibles were then taken and recorded in a laboratory

notebook.

Following the transfer of sediment pellets into the relevant crucibles, the crucibles

themselves were placed collectively in a tray, and were then placed in an OSK 9519A

Drying Oven from between 12-14 hours at 60 degrees Celsius, or until a constant

weight was achieved for individual crucibles with the sediment pellet. The crucibles

were then removed from the drying oven and placed immediately in a desiccator with

fresh silica gel for 30-40 minutes for cooling. The crucibles were then weighed after

cooling and the Dry-Weight in (g.cm 2 ) recorded after correction for crucible weight.

The crucibles were then placed into the Muffle Furnace for 4 hours at 450 degrees

Celsius in order to undergo ashing. The crucibles were allowed to cool to moderate

temperature and then immediately transferred to a desiccator with fresh silica gel. The

crucibles were then re-weighed and the Ashed Weight in grams recorded after

correction for crucible weight. Ash-Free Dry Weight (AFDW) was then calculated by


93

calculating the difference between the dry-weight and the ashed weight, which is

equivalent to the ‘organic matter content’ for that particular sediment sample. This

‘organic matter content’ was expressed as a percentage of the total dry weight and

categorized as Particulate Organic Matter (POM).

The average daily sediment trap collection rate in grams per day was calculated for

each PVC pipe trap by dividing the total dry weight mass of sediments in each trap by

the cross-sectional area of the trap mouth in square centimeters, and further dividing

this figure by the number of days the particular trap was deployed in the study site

collecting sediment (DeMartini et al., 2013; Field et al., 2011). The cross-sectional

area of each sediment trap mouth was calculated using the formula: , and it

was determined that with a sediment trap mouth diameter of 5 centimeters, the cross-

sectional area of each trap mouth was found to be 19.625 cm 2 .


4.4.1 Annual sediment dry weight between sites

The PIS recorded the highest total accumulated sediment weight after a monitoring

duration of twelve months, and incorporating both aspects of seasonality (657.14 g.cm2 ). In the same context the COS, recorded a lower total sediment value of (371.52

g.cm 2 ) (See Table 4.0).

The PIS experienced the highest sedimentation at the start of the monitoring period

which was July 2014 (181.61 g.cm 2 ). This was assumed to be attributed to the

influence of strong winds in the Suva area during this period which caused possible

re-suspension of settled sediment in this site. The COS, however, recorded the highest

amount of sediment received during the month of April 2015 (69.00 g.cm 2 ).


94

Table 4.0 Annual mean and sum of sediment dry weight between study sites

Month/Year

Site, mean and sum sediment dry-weight PIS COS

Mean (g.cm 2 )

Sum (g.cm 2 )

Mean (g.cm 2 )

Sum (g.cm 2 )

July 2014 12.11 ± 0.74 181.61 1.92 ± 0.23 28.87 Aug 2014 1.62 ± 0.34 24.30 2.55 ± 0.31 38.31 Sept 2014 3.05 ± 0.51 45.79 .75 ± 0.19 11.30 Oct 2014 6.12 ± 1.04 91.79 1.08 ± 0.14 16.17 Nov 2014 2.09 ± 0.23 31.30 .86 ± 0.28 12.90

Dec 2014 + Jan 2015*

5.75 ± 0.40 86.26 1.60 ± 0.42 23.94

Feb 2015 4.03 ± 0.79 60.41 1.61 ± 0.19 24.13 Mar 2015 2.96 ± 0.64 44.35 2.59 ± 0.41 38.87 Apr 2015 2.02 ± 0.31 30.32 4.60 ± 0.50 69.00 May 2015 2.20 ± 0.17 32.99 3.96 ± 0.64 59.41 Jun 2015 1.87 ± 0.16 28.02 3.24 ± 0.50 48.62

*Monthly collection unable to be conducted due to a restriction in access to study site due to the December 06, 2014 sewage spill disaster and Environmental Emergency Declaration

It was observed that after an initial high sediment dry weight value for the PIS at the

start of the monitoring exercise in July 2014, a considerable decrease in sedimentation

was noticed in this site until the period November 2014 to January 2015; where a large

increase was again seen. The increase in sedimentation during this period coincided

with the December 06 sewage spill disaster in the Suva Harbour, and this catastrophic

event was presumed to be directly responsible for the increase in sedimentation seen

during this period. A general decrease in sedimentation trend was then observed until

the conclusion of sedimentation monitoring in June 2015 (See Figure 4.4).

Conversely, for the COS a relatively lower initial sediment dry weight value was seen

in July 2014; and similar to the PIS, a steady decline in sediment dry weight was

observed until the month of November 2014. A steep increase in sedimentation was

then noticed in this site from November 2014 to April 2015; where a steep decrease

was then noticed from the latter date until the conclusion of monitoring in June 2015.

Similar to the PIS, the increase in sedimentation observed from November 2014 in the

COS can also be attributed to the Suva Harbour sewage spill disaster; an occurrence


95

which would have greatly impacted normal sedimentation regimes in this general

region.

Figure 4.4 Mean sedimentation between study sites

Sediment dry-weight: Differences analysis using the Mann-Whitney U test

The Mann-Whitney U test was performed in order to investigate whether a statistically

significant difference in sediment dry-weight existed between study sites for the entire

monitoring duration.


investigate for the presence of any statistically significant difference in sediment dry-

weight between study sites:

Ho: There is no statistically significant difference in sediment dry-weight between the

two study sites

Ha: There is a statistically significant difference in sediment dry-weight between the

two study sites


96

Upon interpretation of the results of the Mann-Whitney test and by looking at the

asymptotic significance for the below table (U= 10733.500, p-value < 0.05), it can be

observed that there is a statistically significant difference in sediment dry-weight

between the PIS and the COS. The null hypothesis can therefore be rejected. Based on

the mean rank value generated for both sites it was learned that a greater total sediment

dry-weight amount was found in the PIS (177.42), compared to the COS (147.95) (See

Table 4.1).

Table 4.1 Mann-Whitney U test results for sediment dry weight between sites

4.4.1.1 Dry weight and seasonality

In terms of mean sediment dry-weight between study sites in alternating seasons, there

is a difference in dry-weight observed for both study sites, in each separate season.

The PIS recorded a mean value of 3.96 grams of sediment in the dry season, and a

lower value of 3.37 grams in the wet season. The COS also recorded a higher sediment

dry-weight value of 2.79 grams in the dry season and 2.25 grams in the wet season.

It is evident from the table below that both study sites recorded the highest

sedimentation values (in terms of dry-weight) in the dry season, with lower dry-weight

values for both sites observed for the duration of the wet season (See Table 4.2).

Table 4.2 Mean sediment dry-weight in alternate seasons between sites

4.4.2 Annual Particulate Organic Matter load between sites

The PIS recorded the highest total Particulate Organic Matter (POM) content as a

composition of the total dry-weight (107.51 g.cm 2 ), compared to the COS throughout

both wet and dry seasons, and after a monitoring duration of twelve months. The COS

recorded a comparatively lower total POM content value of (43.37 g.cm 2 ), which was

Significance value


0.005 10733.500 177.42 147.95

Site, Season, and dry weight mean Dry Wet

PIS COS PIS COS 3.96 2.79 3.37 2.25


97

accumulated for the same duration of study and throughout both seasons (See Table

4.3). Large amounts of brown algae fragments, small gastropods, as well as small

crustaceans were observed in sediment collected from the PIS, and due to time

constraints these materials were not filtered out and the sediment samples were

subsequently processed inclusive of these organic materials. It can be assumed, that

the aforesaid organic matter did have an influence on overall total POM content values

specific to the PIS.

The highest POM content in sediment from the PIS was observed at the start of the

monitoring period which was July 2014 (40.18 g.cm 2 ). The COS recorded the highest

amount of POM during the month of April 2015 (11.21 g.cm 2 ). The total mean POM

for the PIS was found to be 0.53 g.cm 2 , compared to 0.39 g.cm 2 for COS.

Table 4.3 Annual mean and sum of sediment POM between study sites

Month/Year

Site, mean and sum POM PIS COS

Mean (g.cm 2 )

Sum (g.cm 2 )

Mean (g.cm 2 )

Sum (g.cm 2 )

July 2014 2.68 ± 0.29 40.18 .18 ± 0.02 2.64 Aug 2014 .30 ± 0.08 4.53 .37 ± 0.06 5.50 Sept 2014 .48 ± 0.08 7.23 .14 ± 0.03 2.09 Oct 2014 .85 ± 0.14 12.74 .10 ± 0.01 1.49 Nov 2014 .29 ± 0.03 4.28 .27 ± 0.20 4.11

Dec 2014 + Jan 2015*

.71 ± 0.06 10.60 .14 ± 0.03 2.13

Feb 2015 .93 ± 0.35 14.01 .13 ± 0.02 1.96 Mar 2015 .28 ± 0.05 4.13 .20 ± 0.03 3.04 Apr 2015 .23 ± 0.03 3.38 .75 ± 0.16 11.21 May 2015 .26 ± 0.02 3.89 .26 ± 0.04 3.85 Jun 2015 .17 ± 0.02 2.54 .36 ± 0.14 5.35


For the PIS it was observed that POM decreased sharply from the month of July 2014

to August 2014. This steep decrease in POM correlated with the correspondingly large

decrease in sediment dry-weight for this site which was seen from July 2014 to August


98

2014. Furthermore, from August 2014 to October 2014 a sharp increase in POM in the

water column of this site was also observed, with a slower decrease gradient continuing

on to November 2014. Interestingly, a sharp increase in POM was again observed from

November 2014 to February 2015; with the outcome of this occurrence being

attributed to the December 06 Suva Harbour Sewage Spill disaster. The increase in

POM content in this site through sewage pollution in the water column, would be

brought about by the direct increase in phytoplankton abundance which utilise

dissolved nitrates in eutrophic conditions. A decrease in POM was then observed from

February 2015 to March 2015 until a gradual decrease was again seen until May

2015.The steady decline then continued from May 2015 until the conclusion of

monitoring in June 2015.

Contrary to the PIS, the COS saw a sharp increase in POM from July 2014 to August

2014. A sharp decrease in POM was then observed from August 2014 to September

2014. A gradual decrease was then observed till October 2014, until a steep increase

was again observed extending towards November 2014. A decrease in POM was then

seen until December 2014 and January 2015, and continued on till February 2015. A

steep increase was then seen until April 2015, with a steep decrease in POM then

continuing till May 2015. A gradual increase was then observed until the conclusion

of monitoring in June 2015. (See Figure 4.5).

Figure 4.5 Mean POM between study sites


99

Sediment POM: Differences analysis using the Mann-Whitney U test


significant difference in sediment POM existed between study sites for the entire

monitoring duration.


investigate for the presence of any statistically significant difference in sediment POM

between study sites:

Ho: There is no statistically significant difference in sediment POM between the two

sites

Ha: There is a statistically significant difference in sediment POM between the two

sites

Based on the results of the Mann-Whitney test and the asymptotic significance in the

below table (U = 12588.00, p-value < 0.528), it can be discerned that no statistically

significant difference in total annual POM content between the PIS and the COS exists.

Therefore, there is insufficient evidence in the data to reject the null hypothesis. The

mean rank values of the PIS (159.18) and the COS (165.74) in terms of total annual

POM content, are within range of each other (See Table 4.4). This finding can be

explained by relating the fact that both study sites are located within the general

vicinity of the Suva Harbour; and were thus both equally exposed to the deleterious

effects of the December 06 sewage spill disaster; and the resultantly high POM content

in the water column brought about by the proliferation of phytoplankton.

Table 4.4 Mann-Whitney U test results for sediment POM between sites

4.4.2.1 POM and seasonality

Mean particulate organic matter (POM) composition in the dry-weight of collected

sediment from both study sites was found to be the highest in in the dry season. This

trend was also similarly observed in the sediment dry-weight aspect of study.

Significance value


0.528 12588.000 159.18 165.74


100

The PIS recorded a mean value of 0.65 grams of POM in the dry season, and a lower

value of 0.38 grams in the wet season. The COS also recorded a higher POM value of

0.42 grams in the dry season and 0.35 grams in the wet season (See Table 4.5).

Table 4.5 Mean sediment POM in alternate seasons between sites

4.4.2.2 POM percentage in sediment dry-weight between sites

From the below table (See Table 4.6), it can be seen that higher percentages of POM

composition in sediment dry weight, were found in sediment retrieved from the PIS

compared to the COS for the duration of monitoring work. This can be attributed to

the variation in the amount of sediment collected from each study site; as the PIS

generally receives a higher influx of sedimentation, and a higher amount of particulate

organic matter would consequently be present in sediment as a result of this. In

addition to this, the PIS is also subjected to higher amounts of direct anthropogenic

pollution i.e. sewage intrusion due to its extremely close proximity to an urban

landmass.

site, season, and dry weight mean Dry Wet

PIS COS PIS COS 3.96 2.79 3.37 2.25


101

Table 4.6 Mean and sum of POM percentage in dry-weight between sites

Month/Year

Site and POM% in sediment dry-weight PIS COS

Mean (g.cm 2 )

Sum (g.cm 2 )

Mean (g.cm 2 )

Sum (g.cm 2 )

July 2014 26.20 ± 4.49 393.07 10.19 ± 1.20 152.86 Aug 2014 21.91 ± 5.13 328.67 18.42 ± 4.41 276.28 Sept 2014 16.96 ± 1.92 254.43 27.62 ± 6.36 414.33 Oct 2014 13.21 ± 1.07 198.09 10.56 ± 1.61 158.44 Nov 2014 14.05 ± 0.50 210.73 18.22 ± 6.18 273.35

Dec 2014 + Jan 2015*

12.01 ± 0.49 180.21 10.27 ± 0.52 154.07

Feb 2015 17.29 ± 2.51 259.37 7.85 ± 0.48 117.73 Mar 2015 13.35 ± 2.07 200.30 8.32± 0.54 124.81 Apr 2015 11.70 ± 0.53 175.45 14.89 ± 2.61 223.38 May 2015 11.71 ± 0.21 175.71 6.27 ± 0.15 94.06 Jun 2015 8.88 ± 0.31 133.14 8.97± 1.73 134.58


It was observed that for the PIS, there was a major steep decrease in POM percentage

in sediment dry-weight at the start of the monitoring period from July 2014 to October

2014. A steep increase was then observed continuing from October 2014 toward

November 2014, where a steep decrease was then again seen till December 2014 and

January 2015. Another steep increase in POM percentage in dry-weight was then seen

until February 2015, with a steep decrease again seen until March 2015. A decrease in

POM percentage in dry-weight was then seen from March 2015 to April 2015, with a

slight and gradual increase then noted toward May 2015. A drastic decrease was then

observed from May 2015 until the conclusion of monitoring work in June 2015.

For the COS a steep increase in the POM percentage in dry-weight was observed from

the start of monitoring in July 2014 till September 2014. This was contrary to the

occurrence in the PIS which saw a steep exponential decrease in POM content during

the same period. A drastic decrease in POM content was then observed from

September 2014 till October 2014; which was similar to the decrease in POM content

seen in the PIS for this same period. An increase in POM content in dry-weight was

then observed in this site until November 2014. A steep then steady decrease was then


102

noted continuing until February 2015, until a gradual increase in POM content in dry-

weight was then again observed until March 2015. A steep rise in POM content in

dry-weight was then noted until April 2015, with another sharp decrease continuing

till May 2015. A sharp rise was then observed until the conclusion of monitoring in

June 2015.

Figure 4.6 Mean POM percentage in sediment dry-weight between study sites

POM percentage in sediment dry-weight: Differences analysis using the Mann-

Whitney U test

The Mann-Whitney U test was then performed in order to investigate whether a

statistically significant difference in POM percentage in sediment dry-weight existed

between study sites for the entire monitoring duration.


investigate for the presence of any statistically significant difference in POM

percentage in sediment dry-weight between study sites:

Ho: There is no statistically significant difference in monthly POM percentage in total

sediment dry-weight between the two sites


103

Ha: There is a statistically significant difference in monthly POM percentage in total

sediment dry-weight between the two sites

There is a statistically significant difference (U = 10045.00, p-value > 0.000) in POM

percentage in total sediment dry-weight between the two sites. Therefore the null

hypothesis can be rejected.

Looking at the mean ranks in the below table (See Table 4.7), it is made evident that

the PIS recorded higher monthly percentages of POM in total sediment dry-weight

(187.12), compared to the COS (143.88). This comparatively high POM percentage in

sediment dry-weight for the PIS, can be attributed to increased phytoplankton

concentrations in the water column arising as a consequence of the December 06

sewage spill disaster in the Suva Harbour.

Table 4.7 Mann-Whitney U test results for POM content in sediment dry weight between sites

4.4.3 Average Daily Sediment Trap Collection Rate (ADTCR)

Upon initial observation of the monthly mean and sum values for ADTCR in each site

shown in the below table (See Table 4.8), it can be inferred that the PIS presented with

higher ADTCR values for a majority of monitoring months in comparison to the COS;

with this site also earlier presenting with a significantly higher total annual sediment

dry-weight value.

Significance value


0.000 10045.000 187.12 143.88


104

Table 4.8 Mean and sum of ADTCR in terms of sediment dry-weight between sites

Month/Year

Site and ADTCR of sediment (dry-weight) PIS COS

Mean (mg.cm 2 )

Sum (mg.cm 2 )

Mean (mg.cm 2 )

Sum (mg.cm 2 )

July 2014 16.67 ± 1.26 250.00 1.33 ± 0.91 20.00 Aug 2014 .67 ± 0.67 10.00 2.00 ± 1.07 30.00 Sept 2014 4.67 ± 1.33 70.00 .00 ± 0.00 .00 Oct 2014 9.33 ± 1.53 140.00 .00 ± 0.00 .00 Nov 2014 1.33 ± 0.91 20.00 .00 ± 0.00 .00

Dec 2014 + Jan 2015*

5.33 ± 1.33 80.00 .00 ± 0.00 .00

Feb 2015 6.67 ± 1.59 100.00 .67 ± 0.67 10.00 Mar 2015 4.67 ± 1.33 70.00 4.67 ± 1.33 70.00 Apr 2015 2.00 ± 1.07 30.00 6.67 ± 1.26 100.00 May 2015 .00 ± 0.00 .00 5.33 ± 1.33 80.00 Jun 2015 .00 ± 0.00 .00 5.33 ± 1.33 80.00


For the PIS it was noticed that from the first month of monitoring in July 2014 to the

month of August 2014, a steep decrease in ADTCR occurred. This occurrence was the

opposite of what was noticed in the COS, whereby, an increase in ADTCR was seen

in this site from July 2014 to August 2014. A steep and prolonged increase in ADTCR

was then observed in the PIS from August 2014 to October 2014. For the COS a

decrease in ADTCR was seen from August 2014 to September 2014, with a prolonged

lack of daily sedimentation until December 2014 and January 2015. The PIS

experienced a steep then gradual increase in ADTCR from November 2014 till

February 2015; with the COS experiencing a gradual then steep increase in ADTCR

from December 2014 and January 2015 until April 2015. The PIS then experienced a

prolonged and steep decrease in ADTCR from February 2015 till May 2015; with no

sedimentation recorded from the month of May 2015 until the conclusion of

monitoring in June 2015. The COS experienced a steady decline in ADTCR from April

2015 until May 2015, with a consistently high ADTCR value observed in this site until

the conclusion of monitoring in June 2015 (See Figure 4.7).

Ronal Lal CHAPTER FIVE

105

Figure 4.7 Mean ADTCR in terms of sediment dry-weight between study sites

ADTCR in terms of sediment dry-weight: Differences analysis using the Mann-

Whitney U test


significant difference in ADTCR in terms of sediment dry-weight existed between

study sites for the entire monitoring duration.


investigate for the presence of any statistically significant difference in ADTCR in

terms of sediment dry-weight between study sites:

Ho: There is no statistically significant difference in ADTCR between the two sites

Ha: There is a statistically significant difference in ADTCR between the two sites

There is a statistically significant difference (U= 11296.500, p-value > 0.001), in

Average Daily Trap collection Rate between the two sites. Therefore the null

hypothesis can be rejected.


106

Looking at the mean ranks in the below table, it is evident that the PIS recorded higher

ADTCR values in monitoring months (179.54), compared to the COS (151.46) (See

Table 4.9). This finding proved to be quite interesting as the PIS was expected to

generate the highest ADTCR, however, looking at the mean rank value pertinent to the

COS, it was noted that this site also generated noteworthy ADTCR values. Relative to

this, it can be stated that due to the high current velocity environment at the COS, a lot

of carbonate sand sediment resuspension was observed in this site; with carbonate sand

and coral rubble comprising of the majority of sediment collected in traps in this site.

Therefore, this occurrence would have contributed to the high ADTCR values seen in

this control site. In the PIS, it was observed in Table 4.6 that this site received

periodically high influxes of sedimentation e.g. July 2014, October 2014, and February

2015; compared to the control site.

Table 4.9 Mann-Whitney U test results for ADTCR in terms of sediment dry-

weight between sites

4.5 Conclusion

4.5.1 Sediment dry-weight between study sites

In terms of sediment dry-weight between study sites, the PIS recorded a significantly

higher total annual percentage of sediment in terms of dry-weight, compared to the

COS. This can be expected as the PIS is an inshore reef ecosystem which is subjected

to a high magnitude of anthropogenic stressors, and is located in close proximity to a

river mouth. In this context, the COS is a more ideal offshore reef ecosystem which

does not receive sedimentation influx of a magnitude of that which was seen in the

PIS.

With regards to the nature of sediment found between sites, it was noticed that no silt

or mud sediments were found in sediment collected from the COS, however, it was

visually observed that a lot of carbonate sand was frequently present in traps from this

site; with this presumably attributed to sediment resuspension through high current

action, which was typical of environmental conditions in this control site.

Significance value


0.001 11296.500 179.54 151.46


107

The nature of sediment collected from the PIS, however, typically had a silty and

muddy texture. This observation can be explained by considering the close proximity

of this site to the mouth of the Tamavua River, and the influx of deltaic deposits which

would arise from overland runoff carried by this river. Additionally, the PIS is also

located in relatively close proximity to a mangrove swamp, and it can be expected that

sediment of a silty and muddy texture will be found in sediment traps deployed in this

location.

4.5.2 Sediment dry-weight and seasonality

The PIS and the COS both recorded high sediment dry-weight percentages in the dry

season, with comparatively lower percentages of dry-weight in the wet season.

According to a Fiji Meteorological Information Sheet, the dry season in Fiji falls

between May and October, with the wet season experienced from November to April.

However, this was contrary to what was experienced during the first four months of

monitoring work for this study (July 2014 to October 2014); whereby constantly rainy

and wet conditions were observed, and which went unabated until February 2015.

4.5.3 Annual Particulate Organic Matter between sites

The PIS presented with the highest annual POM as a percentage of the sediment dry-

weight. The COS showed a considerably lower annual POM percentage in sediment

dry-weight which was expected as this site is not exposed to a high magnitude of

anthropogenic stressors. This interesting finding which reports on unusually high POM

content in the water column in the PIS, can also serve to substantiate the assumption

that the sustained and persistent survival of coral species in this environment, could be

attributed to the uptake of POM by coral as a compensatory survival response during

reduced photosynthetic activity in light deprived conditions.

4.5.4 POM and seasonality

It was observed that both study sites presented with higher mean POM in sediment

dry-weight values in the dry season. For both study sites it was noticed that POM

content was the highest in the first six months of the monitoring study, with this period

classified predominantly under the “dry season”. Although this period of monitoring

was stipulated as a dry-period in the Fiji Islands, constantly rainy conditions were

experienced in both sites from the start of monitoring in July 2014, till February 2015.


108

A major factor influencing this aspect of the study was the December 06 sewage spill

disaster in the Suva Harbour area, whereby, high POM matter (phytoplankton) in the

water column would arise as a result of high amounts of available dissolved nitrates.

4.5.5 POM percentage in sediment dry weight between sites

The PIS recorded overall higher percentages of POM composition in sediment dry-

weight, in comparison to the sediment samples retrieved from the COS. This

occurrence was attributed to the higher influxes of sedimentation (dry-weight), which

was observed and collected from the PIS, and which would positively correlate with

higher POM values. In addition to this, large amounts of brown algae, gastropods, and

small crustaceans were frequently found in sediment traps from this inshore site, and

this would have influenced overall POM content values. The sedimentation (dry-

weight) collected from the COS was very minimal in comparison to the amounts of

sediment periodically received from the PIS.

4.5.6 Average Daily Sediment Trap Collection Rates between sites

The PIS presented with significantly higher ADTCR values, compared to the COS,

with this primary site also presenting with significantly higher total annual sediment

dry-weight values. This can be explained by taking into account the location of each

study site, as well as important environmental conditions which influence sediment

deposition and resuspension. The PIS is an extremely inshore environment (400 meters

from the mainland), and is a comparatively placid reef environment. It is influenced

by current action but not to the extent of that which is seen in the COS. Large amounts

of sediment are deposited in this inshore site through periodic discharges from the

Tamavua River mouth, as well as through storm water drains and outlets from the

mainland during rainy conditions. This site is influenced by sediment resuspension but

not on a consistently daily basis, as compared to the COS. The control site is an

offshore high current energy environment, and also due to its relatively shallow depth

profile (1.5-4.0 meters), daily sediment resuspension of carbonate sand along with the

constant presence of coral rubble is seen in this environment.


109

CHAPTER FIVE

LONG-TERM MONITORING OF IN-SITU TEMPERATURE, LIGHT

INTENSITY, SALINITY, AND DISSOLVED OXYGEN VALUES IN TERMS

OF STRESSOR MAGNITUDE IDENTIFICATION

5.1 Introduction

5.1.1 Environmental conditions in coral resistance

Coral resistance in shallow water environments can be attributed to the influence of

cloud cover, winds, inshore currents, wave action, and location-specific bathymetry;

factors which help in changing local temperature conditions, water motion, irradiance,

as well as a host of associated biological and physical factors known to bring about

coral bleaching (Jokiel & Brown, 2004). This occurrence has been noted at a particular

site within the Suva foreshore where the persistent presence of reef building corals of

the genera Acropora, Porities, and Pocilliopora was observed, despite the influence

of unfavourable variables such as freshwater influx through storm water drains, high

turbidity through large sedimentation input, oil pollution from the Suva Wharf, and

possible eutrophication through sewage input at the Nabukalou Creek entrance.

As is applicable to the study site in this investigation, literature states that localised

coral bleaching events are frequently attributed to anthropogenic stressors including

that of freshwater influxes and pollution, with the prevention of this occurrence

achieved through the inhibition of the particular stress at its origin (West, 2003). The

study site is also reportedly highly polluted with dangerous levels of Tributyltin (TBT)

in molluscs gathered within the harbour; and workers have also reported on the

pollution in the harbour (Garimella et al., 2002; Naidu & Morrison, 1994). However,

the sustained presence of coral species in this situation can be justified by Dubinsky

and Stambler (2011) who state that tolerance which occurs in polluted populations may

be attributed to the fact that detoxification mechanisms present within coral are

sufficient to deal with elevated exposures to the pollutants, or due to dispersal and

mixing between contaminated regions and that of reference populations. The study

also relates that corals acclimate to their polluted surroundings through a

compensatory physiological response, and that this pre-exposure to chemicals can help


110

to induce and enhance the detoxification process; dramatically supplementing their

resilience and persistence in stressful environments.

5.1.2 Resilience and coral reef sustainability

It has been acknowledged that resilience is comprised of two key factors; the ability

of a community in surviving or resisting a disturbance, and the rate at which that

community can recover to its original condition (McClanahan et al., 2012). The

factors which determine coral reef recovery are high levels of coral recruitment in

order to re-establish bleached locations, the presence of suitable substratum for coral

settlement, and low macro algae cover. Resilience of corals in unfavourable

environments can therefore be attributed to the ability of a reef in exchanging genetic

diversity through the interchange of larvae with other adjacent coral reefs through a

mutual connectivity basis (Oppen & Gates, 2006).

This interchange is vital due to the fact that the acquisition and integration of new

genetic alleles through reproduction would consolidate and augment the ability of the

reef to withstand certain disturbances through selection; due to these newfound genetic

alleles incorporating disturbance resistance and resilience properties. Moreover,

stress-resistant coral species which display reduced susceptibility to thermally driven

mortality are considered a fundamental resistance factor in climate change. Also, the

presence of stress-resistant symbionts i.e. zooxanthellae which are less vulnerable to

heat stress and high annual temperature variation on any particular reef, serves to

promote coral tolerance in irregular temperature conditions (McClanahan et al., 2012).

It is imperative that further knowledge be acquired in this area in order to significantly

supplement efforts directed towards coral restoration and replanting activities in

bleached areas.

5.1.3 Algal symbionts in acquired thermal tolerance

Evidence from studies have shown that corals containing different variants of algal

symbionts do vary in their response to bleaching events; with an overall change in the

community structure of these symbionts occurring during the onset of environmental

change. In a study involving algal symbionts and coral adaptive response Baker et al.

(2001) found that corals containing unusual algal symbionts which exhibit thermal

tolerance in high temperature environments, were found to be highly prevalent on reefs


111

which had been impacted by climate change. Baker et al. (2001) explains that these

devastated reefs now hold more potential for future resistance to thermal stress as a

significantly longer extinction time for surviving coral would now be entertained; as a

result of the initial adaptive shift in symbiont communities. Surprisingly, the study also

found that corals from the genus Porites were most notably found on devastated reefs

despite the fact that they did not contain the thermally-tolerant Clade –D variant of

symbiont. This occurrence was also noted in that of our PIS, where predominance in

Porites corals was observed. There is therefore a need to examine certain

environmental variables within the PIS in order to gain further insight on the

persistence of these corals in adverse conditions.

5.1.4 Photosynthetic Photon Flux Density (PPFD)

Photosynthetically Active Radiation (PAR) is defined as the amount of active or

available light radiation for the process of photosynthesis; usually between the

wavelengths of 400 to 700 nanometres. Photosynthetic Photon Flux Density (PPFD)

is used to quantify PAR and describes the number of photons of light contacting a

given area in a given amount of time; and is represented in micromoles per meter

square per second (µmol m 2� s 1� ). PPFD or light intensity is critically important to

the health of corals, whereby, in conditions with diminished light availability, and

where the minimum light requirements of zooxanthellae algal cells is not met, the

zooxanthellae cells may eventually perish through reduced photosynthetic activity.

5.1.5 Zooxanthellae and light intensity tolerance

Zooxanthellae algal cells possess the ability to adapt to variable levels of light

intensity, however this potential is largely dependent upon the past exposure of the

algal cells to sunlight. A study in Hawaii investigating the light requirements of the

scleractinian coral Pocillopora damicornis (See Figure 5.0), found that maximum

photosynthesis in the zooxanthellae algal cells of this coral species took place at a low

light intensity (PPFD) of approximately 200 µmol m 2� s 1� (Riddle, 2013). This

occurrence is explained by the fact that Hawaiian Pocillopora species typically host

clade C zooxanthellae; strains of which have demonstrated reduced tolerance of high

light intensity. Furthermore, it was discovered that in the natural environment this

coral reached photosaturation in the early morning, and tended to regulate


112

photosynthetic processes throughout the rest of the day; which was contrary to the

findings from other researchers which demonstrated a rise in the rate of photosynthesis

in the latter part of the day, and correlated with a decrease in light intensity.

Figure 5.0 Maximal light intensity requirement of Pocillopora damicornis coral (Riddle, 2013)

In a continuation of the same study, the researcher also evaluated the light intensity

requirements of the coral Porites lobata (See Figure 5.1), which is common in shallow

water environments. It was found that maximal photosynthetic activity in this coral

species took place at a light intensity (PPFD) value of about 350 µmol m 2� s 1� , with

no photoinhibition observed at the maximum experimental value of 590 µmol m 2� s1� (Riddle, 2013). The researcher interprets the above findings to be indicative of the

tolerance of Porites lobata to intense lighting, even though it does not harness most of

the available light for photosynthesis. The ability of Pocillopora damicornis in

harnessing light intensity during low light conditions for maximum photosynthetic

function was also a noteworthy finding, with a similar study also demonstrating the

photosynthetic efficiency of some coral species in low light conditions (Kinzie &

Hunter, 1987).


113

Figure 5.1 Maximal light intensity requirement of Porites lobata coral

(Riddle, 2013)

5.1.6 Eutrophication and Dissolved Oxygen

Research conducted in Thailand evaluating the impacts of storm water runoff and

sewage discharge in coastal waterways and reef communities; discovered that these

stressors bring about a decrease in dissolved oxygen levels in coastal water through

the proliferation of microbial populations. Furthermore, it was found that the increased

presence of nutrients through wastewater influxes also facilitated algal blooms,

causing significant changes in the percentage cover of corals and the depletion of

critical fish species in the reef communities. It is found that these disturbances cause

alterations in reef fish community compositions; which in turn increase the

vulnerability of reef fish communities (David et al., 2006). It was stated that water

quality parameters in the study areas were considerably worse in the wet season; with

this being attributed to freshwater runoff inputs and the subsequent perturbation of

sediments on the coastal floor. In this regard, it was found that dead corals were more

abundant in locations experiencing poor water quality, with a proliferation in macro

algae at locations experiencing turbidity and eutrophication; with low coral cover

(Reopanichkul et al., 2010).

It is known that corals have the ability to tolerate and adapt to reduced oxygen

concentrations, however, this tolerance threshold is primarily determined by the

concentration and duration of exposure to this reduced oxygen stressor variable (Haas

et al., 2014). In the event that the reduced oxygen tolerance levels are exceeded, the


114

rapid loss of coral tissue and mortality ensues; with hypoxic water conditions

reportedly being the main causal agent for coral tissue loss in interactions involving

corals and Macro Algae. In the findings of a study investigating reduced dissolved

oxygen concentrations on the physiology of hermatypic corals and benthic algae, it

was reported that dissolved oxygen concentrations in coral reef ecosystems which are

dominated by algae, can reach concentrations as low as 4 MgL 1� (Haas et al., 2010).

The above findings are in direct contradiction with the occurrence at the PIS, whereby

there is a notable presence of isolated but healthy coral growth despite the significant

influence of fresh water runoff influx from that of storm water pipes located at certain

intervals along the length of the Suva foreshore sea wall. It was also noted during a

pilot reconnaissance study to the primary site that dissolved oxygen concentrations

were as high as 7.12 Mg L at 2.5 meters below the surface of the water. In addition to

this, it is believed that the presence of algal blooms in the PIS area is a direct result of

sewage intrusion into the water system. It is known that eutrophication resulting from

sewage intrusion brings about several unfavourable conditions through nutrient

enrichment. This nutrient influx stimulates macro algal growth whereby the enhanced

growth of certain species of macro algae are directly related to nutrient availability;

with small increases in dissolved organic nutrients and particulate organic matter

directly correlating with a proliferation in macro algal populations.

In this way macro algae presence is noted as an important reef health indicator due to

the fact that the abundance of this algae brings about a substantial decrease in coral

photosynthetic productivity through limited light availability, and a change in surface

properties through sedimentation. In terms of alteration to the reef trophic structure a

reduction in coral larval recruitment is usually typical of macro algal blooms along

with outbreaks of coral-feeding crown-of-thorns starfish, and in some cases

replacement of the actual corals with the macro algae itself (Fabricius, 2011).

However, Crown of Thorns Starfish Acanthaster planci was not visible during an

exploratory dive into the PIS area, as well as in the control study site.


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5.1.7 Salinity and its impact on coral fertility

Variation in salinity is a valuable parameter in determining coral habitat water quality

due to the fact that crucial preliminary stages in the development of coral reefs such as

that of fertilisation, metamorphosis and settlement, and fertilisation are significantly

dependant and sensitive to variation in water quality levels (Humphrey et al., 2008). It

has been acknowledged through literature that the interactive effects of suspended

sediments, salinity variation, and nutrients within environmentally pertinent values

have brought about adverse effects to the reproductive success rates of corals

themselves. A healthy and unimpeded reproductive cycle is imperative to the

persistence and resilience of coral reefs following that of a disturbance due to the fact

that this directly pertains to the rate at which the colony will recover and re-establish

itself. In a study highlighting the effects of salinity variation on reproduction it was

found that a reduction in salinity from 35- 28 ppt (parts-per-thousand), significantly

undermined successful fertilisation, and further resulted in a 50% impairment in

development in terms of active and motile swimming planulae larvae (Humphrey et

al., 2008).

The latter study specifically discovered that at a salinity concentration of 30 ppt (parts-

per thousand) there was a marked decline in fertilisation rate; further compounded by

a complete abating of the fertilisation of coral eggs at 28 ppt. This therefore

demonstrates the critical tolerances associated with salinity and its effect on

reproduction; and is further corroborated by a study Richmond (1993), which noted a

sharp drop in fertilisation rates in corals from Guam from 88% to that of 25% following

an induced salinity drop from 34-28 ppt. The study also investigated corals from

Okinawa, Japan and learned that a fluctuation in salinity from 35-31.5 ppt generated a

drop in fertilisation rate from 58% to 34%. It was also further noted that abnormalities

in the developmental stages of corals also frequently occurred at the lower salinity

value of 30 ppt as compared to that of higher salinity levels of 35 and 32 ppt

(Humphrey et al., 2008).

5.1.8 Sea Surface Temperature, solar energy and coral health

The issue of elevated Sea Surface Temperatures (SST) has a direct correlation with

high levels of total solar energy; with a raised threshold of solar energy consequently

bringing about an elevation in sea surface temperature itself (Couce et al., 2012). The


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coral ecosystem health is directly affected as SST has a direct correlation with that of

gas solubility, and inevitable coral bleaching through the thermal stress tolerances of

the corals themselves being surpassed (McCabe et al., 2010). In the aforesaid study,

solar energy was complemented by an increase in water transparency during the

warming period. In addition to this, it was further noted that water transparency in the

study area exhibited a negative correlation with that of wind speed. What this

ultimately meant for the study area was that water transparency was further increased

due to the absence of re-suspended benthic sediments; which would have undergone

excitation through wind aided wave action; with this factor absent in this case.

High levels of solar energy infiltration have also shown to bring about a reduction in

photosynthetic rate for zooxanthellae, coupled with the factor of heat stress. The

abundance and diversity of heat tolerant coral species which host various strains of

zooxanthellae algae, and which have become acclimated to temperature variability, are

therefore vital in providing the best resistance to climate change in terms of rising sea

surface temperature.


The following hypotheses were formulated in order to encompass the nature of

research to be conducted in this chapter.

i. Temperature, light intensity, and Photosynthetically Active Radiation will be

significantly lower in the Dynamite Hut site in comparison to the control site.

ii. Salinity and Dissolved Oxygen values will be significantly lower in the Dynamite

Hut site in comparison to the control site.

The following objective was devised in order to test the aforementioned hypotheses:

i. To construct a coral health Time Line at the (PIS) and at the control site in

order to compare and contrast the magnitudes of relevant ambient environmental

parameters.


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5.3 Methodology

5.3.1 Data loggers and associated equipment

Six HOBO® Pendant® (UA-002-64) Temperature/Light Data Loggers were used

throughout the year-long duration of monitoring. Data loggers of this model are two-

channel loggers designed for depths of up to 30 meters, have 10-bit resolution, and

possess the capability of recording up to approximately 28,000 combined temperature

and light readings or internal logger events. For programming and data retrieval the

loggers are connected via a coupler and Pendant optical base station (BASE-U-1) with

UBS interface to a computer which is installed with HOBOware 2.x software.

5.3.2 Data logger calibration

5.3.2.1 Light Intensity: method for standardised measure

1. Data loggers were pre-set for logging Light Intensity at an interval of ten minutes,

using the optical base station and dedicated HOBO software.

2. Data loggers to be calibrated were placed in equidistant positions from each other,

and outside in sunlight for a thirty minute duration in order to allow for access to

an even amount of diffused light.

3. Data loggers were then retrieved and connected to a computer using the optical

base station in order to obtain a data readout for each logger for the thirty minute

logging period.

4. Average light level values for each data logger for the thirty minute logging period,

was obtained from the three light intensity values recorded in each of the ten

minute logging intervals.

5. Possible light intensity value deviations between each of the data loggers could

then be observed by comparing the derived average light intensity values, and

recording the deviations specific to each data logger serial number value. (Logger

serial numbers are identified by the HOBO software during individual logger

docking and subsequent data readout).

6. Data set values acquired from data loggers with noteworthy light intensity value

deviations observed during calibration, could then be presented with a standard

error value relative to the specific amount of deviation observed in that particular

data logger in comparison to the other loggers.


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5.3.2.2 Temperature: method for standardised measure

1. Data loggers were pre-set for logging Temperature at ten minute intervals, using

the optical base station and dedicated HOBO software

2. Data loggers to be calibrated were placed in equidistant positions from each other,

in a laboratory water bath.

3. Data loggers were equilibrated for sixty minutes at 30° Celsius in an ISUZU Water

Bath (Serial No. 71150086).

4. Data loggers were then retrieved and connected to a computer using the optical

base station in order to obtain a data readout for each logger for the thirty minute

logging period.

5. Average temperature values for each data logger for the thirty minute logging

period, was obtained from the three temperature values recorded in each of the ten

minute logging intervals.

6. Possible temperature value deviations between each of the data loggers could then

be observed by comparing the derived average temperature values, and recording

the deviations specific to each data logger serial number value. (Logger serial

numbers are identified by the HOBOware software during individual logger

docking and subsequent data readout).

7. Data set values acquired from data loggers with noteworthy temperature value

deviations observed during calibration, could then be presented with a standard

error value relative to the specific amount of deviation observed in that particular

data logger in comparison to the other loggers.

Calibration experiments performed between all six loggers in both the temperature and

light intensity variable category yielded approximately similar average results, due to

the presence of individual values with very minor deviations in each ten minute

interval. The calibration exercise was performed before the start of the year-long

monitoring study.

5.3.3 Study site field deployment

Two data loggers were deployed in each study site for one month at a time, whereupon

each logger was retrieved and replaced with a fresh logger immediately. In order to

acquire an accurate representation of temperature and light intensity variation within

each study site, and in order to factor in the variation in depth observed between


119

Quadrat 1 and Quadrat 5 on the reef slope in each study site; one logger in each study

site was deployed in the shallow area (Quadrat 1 for both sites), with one logger in

each study site deployed in the deepest area (Quadrat 5 for both sites).

Each logger was pre-programmed with the HOBOware software and BASE-U-1

station in order to log at ten minute intervals, twenty-four hours a day, and for a period

of one month at a time. The loggers were also programmed for a “trigger start”,

whereby, upon affixation the logger could be deployed by a magnet which was placed

just adjacent to the logger for three seconds in order to initiate data logging.

Four 1.5 meter lengths of ½’’ thick construction rebar iron with the uppermost 10

centimetre section bent at a 180° angle in order to allow a parallel orientation with the

substrate, were hammered into the substrate at the designated locations in each site

with a 4 kg iron mallet, until the bent section of the rebar iron was poised just above

the substrate. A small section of high density foam was then placed upon this 180°

surface, with the logger then secured atop of the foam by way of two plastic cable ties

securing the body of the logger, with an additional cable tie looped through an eyelet

hole at the top of the logger and fastened onto the rebar iron in order to prevent lateral

dislodgment through current action. The logger was positioned with the device light

sensor facing directly skyward (See Figure 5.0).

Figure 5.2 A HOBO data logger freshly deployed in the PIS


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5.3.4 Data logger retrieval, data readout, and data tabulation

Each data logger was retrieved by cutting the fastening plastic cable ties, and then

storing each logger in a predetermined section in a waist pouch (separate sections for

loggers retrieved from shallow and deep depth areas within the site). Upon reaching

the laboratory, each data logger to be read out was thoroughly cleaned in order to

prepare it for docking in a coupler and the BASE-U-1 station. The data was then

downloaded from the logger and stored in a Microsoft Excel spreadsheet and

catalogued for later reference.

In order to acquire accurate mean values in terms of available light intensity per day,

the range of data selected for each day of logger recording only ranged from the period

of available light in the morning (dawn), up until the amount of available light in the

evening (dusk). In order to maintain consistency in the dataset, this was also repeated

for the temperature variable. Monthly data for both variables which was comprised of

cumulative daily values was then plotted in the Software Package for Statistical

Analysis (SPSS) v. 21, in the form of Box and Whisker plots in order to identify the

presence of extreme outliers in the dataset. These extreme outliers were deleted in

order to allow for the derivation of accurate mean values. Following this, the following

categories were then derived for both light intensity and temperature: daily mean, daily

maximum, and daily sum for light intensity and corresponding Photosynthetic Photon

Flux Density (PPFD).

For PPFD calculations the following series of steps were taken:

Light intensity (Lum/ft²) → light intensity (Lux/m²):

Each ten minute logging interval (light intensity lum/ft²) value was multiplied by

10.764 (as 1 lum/ft² = 10.764 Lux)

PPFD (µmol m 2� s 1� ):

Converted daily (Lux/m²) values were multiplied by a multiplier value for Sunlight as

the light source (0.0185) in order to convert illuminance in Lux/m² to PPFD

micromoles per meter square per second (µmol m 2� s 1� ).

Total daily PPFD (µmol m 2� d 1� ):

This final value was obtained by multiplying each ten minute logging interval (PPFD

µmol m 2� s 1� ) value by 600* and obtaining a sum of all ten minute interval logging


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values in order to obtain a single daily PPFD value in micromoles per meter square

per day (µmol m 2� d 1� ). These daily values were then converted to moles per meter

square per day (mol m 2� d 1� ).

* 60 seconds: 1 minute

3600 seconds: 60 minutes

3600 seconds × 12 hours of daily monitoring

= 43,200 seconds

6 logging intervals: 1 hour

72 logging intervals: 12 hours

43,200 seconds / 72 logging intervals

= 600 seconds per logging interval per hour

5.3.5 YSI-85 Salinity, and Dissolved Oxygen measurements

A YSI-85 Salinity, Conductivity, Dissolved Oxygen, and Temperature multi-

parameter probe meter was used to sample Salinity and Dissolved Oxygen values

during each monthly field data collection trip to each study site. The equipment was

first calibrated in terms of the correct height at sea level, with three measurements for

each parameter then undertaken at varying depths: 0.3 meters, 1.5 meters, and 2.5

meters. Cable ties were fastened along the probe wire in correlation with the aforesaid

measurement intervals, in order to confirm the immersion of the probe at

predetermined measurement depths. A small section of 3/8’’ construction rebar iron

was secured directly adjacent to the sensing probe with rubber bands in order to

facilitate the stationary buoyancy of the probe in the midst of current action. Relevant

measurements were recorded in a field data notebook, and average values of each

parameter, was derived from the sampling exercise conducted at the three different

depths


5.4.1 Daily Light Intensity for coral photosynthesis in study sites

Daily light intensity and temperature data values were acquired from data loggers

which were deployed at two different depths within each study site. Depth 1 for each


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site referred to the shallowest region in the site, whereas, Depth 2 referred to the

deepest region in that particular site (See Table 5.0).

Table 5.0 Data logger depth values within each study site

Site Depth 1 (Shallow) Depth 2 (Deep) S1 (PIS) 1.64 Meters 2.15 Meters S2 (COS) 1.93 Meters 3.43 Meters

The following graphs depict daily comparative mean daily light intensity values which

were recorded at two different depths within each study site, every month, and for a

period of one year:

Depth 1 (shallow zone for both study sites):

Figure 5.3 Daily shallow zone comparative light intensity values between sites


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Depth 2 (deep zone for both study sites):

Figure 5.4 Daily deep zone comparative light intensity values between sites

Upon examining the above graphs portraying light intensity values for two different

depth profiles within each site, it becomes evident that the COS presents with

predominantly higher light intensity values on an annual timescale, and in comparison

to the PIS. After comparing light intensity values between sites in Depth 1 (shallow

region in study sites), and Depth 2 (Deep region in study sites) graphs, it can be

inferred that the COS records higher daily mean light intensity values in both the

shallow and deep water categories (See Figure 5.3 and Figure 5.4).

This finding demonstrates that light tends to penetrate further into the water column in

the COS when compared to the PIS for both depth profiles. It can be stated that light

intensity is relatively restricted in the PIS due to frequently turbid conditions, and

periodic incidences of pollution in the area i.e. oil contamination originating from the

adjacent industrial area, and ship repair dry-docks. The following table (See Table

5.1), shows a comparison of daily mean light intensity values for each site which was

derived from daily light intensity sum values, and from this table it was observed that

there were notable differences in mean Light Intensity values recorded in similar depth


124

profiles between study sites. This preliminary difference will be explored further using

a One-Way ANOVA differences test in order to investigate for the presence of any

significant differences.

The following null and alternative hypotheses were therefore proposed in order to

investigate for the presence of any statistically significant difference in Light Intensity

values at different depths between study sites:

Ho: There is no statistically significant difference in Light Intensity values in different

depth profiles present between the two study sites

Ha: There is a statistically significant difference in Light Intensity values in different

depth profiles present between the two study sites

Table 5.1 One-Way ANOVA test results and annual mean light intensity values recorded between sites at similar depth profiles

Site and depth profiles

Total Light Intensity Mean (lum/ft²)

Significance value (interaction between groups)

Site 1 Depth 1 5821.34 ± 5.69140 0.000 Site 1 Depth 2 3941.04 ± 4.53017

Site 2 Depth 1 18065.37 ± 10.19955 Site 2 Depth 2 17196.56 ± 10.75661

After the performing of the One-Way ANOVA test a statistically significant difference

(p-value > 0.000) in light intensity between different depth profiles in each study site

was found. Therefore, the null hypothesis was then rejected.

After it has been established that a significant difference between site and depth profile

groups existed, the exact location of the difference was then determined using the

Tukey HSD (Honestly Significant Difference) post-hoc test, in order to explore

multiple comparisons between the different depth profile groups (See Table 5.2):




Mean difference Significance

Site 1 Depth 1 Site 1 Depth 2 22.58151 ±11.89814 0.229 Site 2 Depth 1 Site 2 Depth 2 18.61969 ± 11.71288 0.385 Site 1 Depth 1 Site 2 Depth 1 167.46861 ± 11.71288 0.000 Site 1 Depth 2 Site 2 Depth 2 171.43043 ± 11.89814 0.000


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A highly significant interaction (p-value > 0.000), existed between the shallow depth

profile in the PIS (Site 1 Depth 1), and the shallow depth profile in the COS (Site 2

Depth 1), with a total mean difference of 167.46861. This finding relates the fact that

significantly higher mean light intensity was seen in the COS compared to the PIS for

the shallow depth profile category throughout the duration of the monitoring period.

There was also a highly significant interaction (p-value > 0.000), between the deep

depth profile in the PIS (Site 1 Depth 2), and the deep depth profile in the COS (Site

2 Depth 2); with a total mean difference of 171.43043. Similar to the shallow depth

profile findings between both study sites, this finding also demonstrates the presence

of significantly higher mean light intensity in the COS for the deep depth profile

category compared to the PIS.

In terms of statistically significant interactions between depth profiles within sites, it

was found that no significant interaction existed between the shallow and deep depth

profile category for the PIS (p- value < 0.22), and also for the COS (p-value < 0.385).

5.4.2 Daily Photosynthetic Photon Flux Density (PPFD) in study sites

Photosynthetic Photon Flux Density values as the amount of active or available light

available for photosynthesis and coral survival was calculated from light intensity data

which was described in the previous section. The following graphs represent daily

PPFD values which were obtained for the different depth profiles within each site that

were also previously defined in the previous section.


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Depth 1 (shallow zone for both study sites):

Figure 5.5 Daily shallow zone comparative PPFD values between sites Depth 2 (deep zone for both study sites):

Figure 5.6 Daily deep zone comparative PPFD values between sites


127

After examining the above graphs relating to daily PPFD values at differing depth

profiles within sites, it becomes evident that a distinction in the range of PPFD values

between sites exists; whereby the COS clearly presents with higher daily PPFD in each

of the two depth profile comparisons made between study sites (See Figure 5.5 and

Figure 5.6). This outcome was expected as high PPFD values would naturally be

correlated with high light intensity values; that of which was seen in the COS and

described in the previous section. Based on previous discussions with the co-

supervisor of this study, it was projected that daily PPFD values should normally be

within range of 2000 µmol m 2� s 1� (Bythell, J, personal communication).

The daily PPFD mean value for both the shallow depth (1066.66 µmol m 2� s 1� ), and

deep depth (800 µmol m 2� s 1� ) profile in the PIS was found to be sufficient enough

for coral photosynthetic activity for some of the coral species present in this primary

site (See Table 5.3). This statement was based on the findings of a study in Hawaii

(mentioned previously), where it was found that maximum photosynthesis in the

zooxanthellae algal cells of the coral species Pocillopora damicornis took place at a

low light intensity (PPFD) of approximately 200 µmol m 2� s 1� . The study also found

that the light intensity requirements of the coral Porites lobata took place at a light

intensity (PPFD) value of about 350 µmol m 2� s 1� (Riddle, 2013). These two

aforementioned species were both found to be present in the primary site of this study.

This observed distinction in PPFD values between sites was also explored further using

a One-Way ANOVA differences test in order to investigate for the presence of any

significant differences

The following null and alternative hypotheses were therefore proposed in order to

investigate for the presence of any statistically significant difference in PPFD values

at different depths between study sites:

Ho: There is no statistically significant difference in PPFD values in different depth

profiles present between the two study sites

Ha: There is a statistically significant difference in PPFD values in different depth

profiles present between the two study sites


128

Table 5.3 One-Way ANOVA test results and annual mean PPFD values recorded between sites at similar depth profiles


Daily PPFD Mean (mol m 2� d 1� )

Daily PPFD Mean (µmol m 2� s 1� )

Significance value (interaction

between groups) Site 1 Depth 1 0.64 ± 0.05329 1066.66

0.000 Site 1 Depth 2 0.48 ± 0.03842 800 Site 2 Depth 1 2.16 ± 0.09555 3600 Site 2 Depth 2 1.96 ± 0.09811 3266.66

After the performing of the One-Way ANOVA test a statistically significant difference

(p-value > 0.000) in PPFD between different depth profiles in each study site was

found. Therefore, the null hypothesis was then rejected.

After it has been established that a significant difference between site and depth profile

groups existed, the exact location of the difference was then determined using the

Tukey HSD (Honestly Significant Difference) post-hoc test, in order to explore

multiple comparisons between the different depth profile groups (See Table 5.4):


A highly significant interaction (p-value > 0.000), existed between the shallow depth

profile in the PIS (Site 1 Depth 1), and the shallow depth profile in the COS (Site 2

Depth 1), with a total mean difference of 1.52149. This finding relates the fact that

significantly higher mean PPFD was seen in the COS compared to the PIS for the

shallow depth profile category throughout the duration of the monitoring period.

There was also a highly significant interaction (p-value > 0.000), between the deep

depth profile in the PIS (Site 1 Depth 2), and the deep depth profile in the COS (Site

2 Depth 2); with a total mean difference of 1.48209. Similar to the shallow depth

profile findings between both study sites, this finding also demonstrates the presence



Mean difference Significance

Site 1 Depth 1 Site 1 Depth 2 0.15996 ± 0.10952 0.462 Site 2 Depth 1 Site 2 Depth 2 0.19936 ± 0.10782 0.251 Site 1 Depth 1 Site 2 Depth 1 1.52149 ± 0.10782 0.000 Site 1 Depth 2 Site 2 Depth 2 1.48209 ± 0.10952 0.000


129

of significantly higher mean PPFD in the COS for the deep depth profile category

compared to the PIS (See Table 5.4).

In terms of statistically significant interactions between depth profiles within sites, it

was found that no significant interaction existed between the shallow and deep depth

profile category for the PIS (p- value < 0.462), and also for the COS (p-value < 0.251).

5.4.3 Annual water temperature in study sites

Similar temperature values were observed for all depth profile categories (described

previously), within and between study sites. Total mean temperature values were

obtained from daily averages recorded simultaneously within both study sites (See

Table 5.5).

Table 5.5 Annual mean temperature between depth profiles in study sites


Annual mean temperature (°C)

Site 1 Depth 1 26.85 ± 0.09 Site 1 Depth 2 26.89 ± 0.09 Site 2 Depth 1 26.84 ± 0.09 Site 2 Depth 2 26.88 ± 0.09

From the above table it is evident that there are similar annual mean temperature values

recorded in different depth profiles within each study site, and between study sites for

the entire monitoring duration. Further data exploratory analysis in terms of

differences tests was not conducted on the basis of this similarity. It was observed from

(Figure 5.7 and Figure 5.8), however, that daily mean temperature values during the

months of February 2015 and March 2015 were particularly high for both depth

categories and within both study sites (See Table 5.6). This period of high temperature

explains the intermittent patches of coral bleaching which was observed in the COS

during these latter stages of monitoring as this site recorded higher maximum

temperature values during this period, compared to the PIS. There was, however, no

coral bleaching observed in the PIS.


130

Table 5.6 Daily mean and maximum temperatures (February 2015 – March 2015)


Daily mean temperature (°C)

Daily maximum temperature (°C)

Site 1 Depth 1 29.68 ± 0.09 31.47 ± 0.07 Site 1 Depth 2 29.73 ± 0.09 31.57 ± 0.07 Site 2 Depth 1 29.67 ± 0.09 32.39 ± 0.09 Site 2 Depth 2 29.79 ± 0.09 32.81± 0.11

With regards to the role of temperature in the PIS ecosystem and on the health of

corals, this important variable can be considered as having that of a temporal stressor

influence in this site; as daily mean and maximum temperatures recorded in different

depth profiles within this site for the months of February 2015 and March 2015 did

exceed 28°C. In relation to this finding, it was found that for corals in the Fiji Islands,

an exposure to temperatures greater than 29°C for more than 60 consecutive days led

to coral bleaching (Morris, 2009; Sykes & Lovell, 2007). Periodically high incidences

of temperature observed from February 2015- March 2015 for both study sites would

have detrimental effects on coral health, in terms of coral bleaching and the expulsion

of zooxanthellae algae from the coral host as a result of heat stress. This occurrence

was evident in the COS through sporadic incidences of coral bleaching, which was

presumably attributed to the high water clarity and increased light penetration inherent

to this site.

The following graphs represent mean daily water temperature in the shallow and deep

depth profiles between study sites:


131

Depth 1 (Shallow zone for both study sites):

Figure 5.7 Daily shallow zone comparative temperature values between sites

Depth 2 (Deep zone for both study sites):

Figure 5.8 Daily deep zone comparative temperature values between sites


132

Daily mean water temperature between both study sites was found to be similar for all

depth profiles, with this finding presumably attributed to the relatively close location

of each individual site to one another in the greater Suva Harbour area. Despite the PIS

being an extremely inshore site, and the COS being located farther offshore, the water

temperature regimes of each site did not differ from one another. The scale of annual

mean water temperature values observed for both study sites also did not exceed the

normal coral survival tolerance range seen for Fiji corals during the 2000 coral

bleaching event.

However, it can be informatively stated that the variable of site temperature does have

a temporal stressor influence on the coral reef ecosystem seen at the PIS, as daily mean

and maximum temperature values obtained during the months of February 2015 and

March 2015 were observed to be unusually high. These periods of high temperature

would have an adverse effect on coral health and would bring about sporadic or

widespread coral mortality through coral bleaching; as was noted in the COS. Coral

bleaching was not observed in the PIS during this period, and it was assumed that a

“shading effect” acquired from the increased turbidity present in the water column of

this site, served as refugia for corals in order to negate the effects of high water

temperatures and coral bleaching.

5.4.3.1 Daily maximum site temperature

Similar daily maximum temperature values were also observed for all depth profile

categories, within and between study sites. Annual maximum temperature values were

derived from daily maximum temperature values from within each respective study

site (See Table 5.7).

Table 5.7 Annual maximum temperature between depth profiles in study

Sites


Daily maximum temperature (°C)

Site 1 Depth 1 27.19 ± 0.07 Site 1 Depth 2 27.20 ± 0.07 Site 2 Depth 1 27.50 ± 0.09 Site 2 Depth 2 27.55 ± 0.11


133

From Table 5.7 it can be seen that similar daily mean maximum temperature values

were recorded in different depth profiles within each study site, and between study

sites. Further data exploratory analysis in terms of differences tests was also not

conducted for this aspect on the basis of this similarity. The following graphs represent

mean daily maximum water temperature in the shallow and deep depth profiles

between study sites (See Figure 5.9 and Figure 5.10):

Depth 1 (Shallow zone for both study sites):

Figure 5.9 Daily shallow zone comparative maximum temperature values


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Depth 2 (Deep zone for both study sites):

Figure 5.10 Daily deep zone comparative maximum temperature values

From the daily mean temperature and daily maximum temperature graphs it can be

seen that the highest values from both of these aspects were recorded between the

months of February 2015 to March 2015 for both study sites. In some instances, daily

maximum temperature was observed to be around 33°C for the COS; with this

occurrence having an abnormally high temporal stressor influence on coral health. In

relation to mean light intensity in study sites for both depth profiles, the highest

recorded values for these categories occurred in the month of November 2014.

5.4.4 Monthly site salinity values between study sites

Monthly salinity values were found to be relatively similar between study sites from

the start of monitoring in July 2014 to September 2014. Slight deviations arose

between sites from the start of October 2014 until April 2015, whereby, during this

period it was noted that monthly salinity values for both study sites started declining;

with the PIS experiencing a more pronounced decline in salinity values in relation to

the COS. Relatively similar salinity ranges for both sites were again seen from the end

of April 2015 continuing on till the start of June 2015 (See Table 5.8).


135

Salinity values in the PIS in February 2015 (27.50 ppt), and April 2015 (27.50 ppt),

reached dangerously low levels which would normally have threatened coral survival.

As it is acknowledged that a reduction in salinity from 35- 28 ppt (parts-per-thousand),

significantly undermines successful coral fertilisation, and also results in a 50%

impairment in the development of active and motile swimming planulae larvae

(Humphrey et al., 2008). This low salinity result was attributed to the heavy rainfall

seen during this wet season period in the Fiji Islands.

Table 5.8 Monthly mean salinity values between study sites

Monitoring for the months of December 2014 and January 2015 was not conducted

due to prohibition of entry into study sites as a result of the December 06, 2014 sewage

spill disaster. Monitoring was resumed in February 2015.

The following histogram illustrates mean monthly salinity values between study sites

for the entire duration of monitoring:

Site Mean Monthly Salinity (‰) 1 2 3 4 5 8 9 10 11 12

COS 35.57 ± 0.09

35.00 ± 0.35

35.87 ± 0.15

33.17 ± 0.54

36.47 ± 0.35

33.50 ± 0.06

33.03 ± 0.38

30.07 ± 1.53

29.83 ± 1.90

32.57 ± 0.37

PIS 35.53 ± 0.22

35.63 ± 0.09

35.03 ± 0.44

32.40 ± 1.51

33.17 ± 0.03

27.50 ± 3.24

31.70 ± 1.15

27.50 ± 3.24

32.53 ± 0.37

31.19 ± 1.08


136

Figure 5.11 Monthly comparative salinity values between study sites

5.4.5 Monthly site dissolved oxygen values between study sites

Monthly mean dissolved oxygen values between study sites were also observed to be

similar for the entire duration of monitoring, with no extreme decrease in this variable

within the range of 4 Mg/L which would typically indicate severe macro algal

dominance (Haas et al., 2014). Further data exploratory tests in order to investigate

significant differences was also not conducted on this aspect of study, and on the basis

of this similarity. The following table depicts monthly mean dissolved oxygen values

between study sites (See Table 5.9).

Table 5.9 Monthly mean dissolved oxygen values between study sites

Monitoring for the months of December 2014 and January 2015 was not conducted

due to prohibition of entry into study sites as a result of the December 06 sewage spill

Site Mean monthly Dissolved Oxygen (Mg/L) 1 2 3 4 5 8 9 10 11 12

COS 6.49 ± 0.27

7.15 ± 0.21

6.74 ± 0.13

6.34 ± 0.57

6.10 ± 0.12

6.30 ± 0.03

6.47 ± 0.30

7.07 ± 0.26

8.09 ± 0.31

6.52 0.29

PIS 5.39 ± 0.12

6.92 ± 0.12

6.10 ± 0.51

6.53 ± 0.07

6.29 ± 0.08

5.39 ± 0.45

5.59 ± 0.07

6.37 ± 0.06

5.71 ± 0.60

6.70 ± 0.16


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disaster. Monitoring was resumed in February 2015. The following graph illustrates

mean monthly dissolved oxygen values between study sites for the entire duration of

monitoring:

Figure 5.12 Monthly comparative dissolved oxygen values between study sites

5.5 Conclusion

5.5.1 Light intensity influence in the PIS

Mean daily light intensity was found to be significantly lower in the PIS compared to

the COS. In relation to this aspect, the amount of daily Photosynthetically Active

Radiation (PAR) was also found to largely differ between the two sites; with the PIS

presenting with markedly lower PAR values compared to the COS. Despite this large

distinction in PAR values between the sites, the PIS still receives a sufficient amount

of daily PAR in order to ensure the survivability of corals. It can then be stated that

the variable of light intensity is not a limiting stressor factor on the relic reef ecosystem

seen at the PIS. This finding also serves to support the observed survival of selected

coral species in the stressed sub-optimal environment of the primary site; with the

knowledge that turbidity from increased sedimentation in this site (discussed in the


138

previous chapter), does not have a significant influence on light penetration and coral

health in the study area, as was initially hypothesised.

The COS recorded significantly higher PAR values compared to the PIS, with

exceptionally high water clarity observed during fieldwork in this site. It was

conjectured that exceedingly high PAR values observed in this site, coupled with

sporadically high temperatures seen between February 2015 and March 2015, may

have contributed to the amount of coral bleaching and significant loss in coral cover

(discussed in chapter one), seen between month 7 and month 12 of monitoring in the

COS.

5.5.2 Mean site water temperature between sites

Mean daily temperature values between study sites were found to be within range of

each other, due to the relative location of each site to one another within the greater

Suva Harbour area. Moreover, daily maximum temperature values between sites were

also similar. The COS recorded slightly higher daily maximum temperature values

compared to the PIS, however, these deviations were not significant enough to warrant

a categorical distinction.

However, although it was found that daily mean temperatures were not excessively

high enough to induce bleaching, it was observed that sporadic incidences of high

temperatures i.e. 34° Celsius, were present in the general dataset. It is projected that

the frequency, duration, and intensity of these temperature “spikes” may have had an

overall influence on the health of corals in the PIS.

5.5.3 Mean monthly Salinity and Dissolved Oxygen in study sites

Mean monthly salinity and dissolved oxygen values between study sites were also

similar in range. The PIS presented with slightly lower salinity values in comparison

to the COS from the start of October 2014 until April 2015, however, these deviations

were not explored further due to the relatively small nature of variations which were

present. It was noted, however, that salinity values reached dangerously low levels in

April 2015 and June 2015. Dissolved oxygen values also did not differ significantly

between sites, and therefore it can be concluded that the variables of salinity and


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dissolved oxygen also do not significantly alternate in magnitude and induce a stressor

influence.

5.5.4 Recommendations for Suva Harbour coral assemblages

In light of the current state of research regarding cases of perpetuated resilience and

sporadic tolerance levels of communities of near-shore coral reefs to anthropogenic

and environmental stressors; a more in-depth and large scale investigation is needed

in order to determine and analyse specific variables and factors responsible for the

interesting presence of corals in the PIS. The positive findings of such a research could

hold potential for coral restoration and replanting efforts; and provide a limited

medium in which the adverse consequences of global warming could be marginally

mediated. Methods used to facilitate such an investigation could comprise the use of

multi-site monitoring programs which would help in producing data and the

identification of variables which link directly to near-shore coral reef resilience.

In this respect, the use of a multivariate modelling program would also assist greatly

in highlighting resistance and resilience variables; and provide a platform for the

development of the model itself in order to observe and analyse the interconnectedness

of certain factors and their associated influences. It has also been proposed that there

are certain actions that can be taken in order to enhance the potential of particular reef

systems in terms of persistence and resilience in present day climatic conditions which

are ever changing. In relevance to this investigation, it has been stated that coral

bleaching events which occur on localised scales are irregular and inconsistent;

however, the deleterious impacts of coral bleaching can be mitigated in these areas

through the intervention and cooperation of Marine Protected Area managers who

exercise thoughtful planning and execute feasible strategies with efficacy and foresight

(West, 2003).

Site selection criteria for resilient coral reefs can be developed through the examination

of coral reef responses to disturbance across a range of past oceanographic and

management conditions (McClanahan et al., 2012). These conditions comprise of

physical factors such as reef hydrographic conditions and connectivity; biological

factors including coral diversity, disease, and herbivory; and habitat factors such and

that of nutrient input, habitat complexity and human impacts (McClanahan et al.,


140

2012). The implementation of a Marine Protected Area could also serve to mitigate

and reduce the stress associated with sedimentation of near-shore reefs through the

establishment and facilitation of prolific populations of herbivorous fish. In this way

the fish species would abate algal growth to a certain extent and allow for the recovery

of sediment affected coral populations through the provision of lag time necessary for

the corals to recover (Halpern et al., 2013).

Ronal Lal CHAPTER SIX

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CHAPTER SIX

GENERAL CONCLUSION AND RECOMMENDATIONS

6.1 Review of objectives

6.1.1 Coral cover and species diversity in the primary site

The following objective was relevant to Chapter Two, which dealt with the long-term

evaluation of coral cover and species diversity between the PIS and COS. With regards

to detailed procedures which were employed in order to achieve these objectives,

please refer to the respective chapters.

1. To identify and compare the health and growth phases of dominant coral

species (Order Anthozoa), between the polluted Walu Bay study site (PIS)

and the more natural reef system at the Dennis’ Patch Reef site (COS).

� Coral cover percentage along with other major categories, was successfully

monitored in the PIS and a control site every month for the period of one year. It

was concluded that monthly coral cover monitoring through the use of permanent

quadrats was very effective in following the health of individual coral colonies in

terms of recording mortality and recovery phases; which then allowed for a

cumulative representation of coral cover and ecosystem health for the entire area of

study.

� Coral cover percentage in the PIS experienced a significant decline between month

1 and month 7 of monitoring, with the December 06 2014 sewage spill disaster in

Suva Harbour not adversely affecting coral cover percentage in this site between

month 7 and month 12 of monitoring as was expected. Conversely, the COS did see

a significant decrease in coral cover between month 7 and month 12 of monitoring

due to the close proximity of this site to the sewage pollution source.

� In terms of the documentation of significant yearly events, the effects of a sewage

spill disaster on the health and diversity of corals in each of the relevant study sites


142

in the Suva Harbour, was also assessed as part of the coral health timeline for both

study sites.

� For a site which is located in very close proximity to the urban city centre of Suva,

the Kings Wharf, Walu Bay Industrial area, and the Royal Suva Yacht Club, the

PIS presented with a higher coral species diversity in all three monitoring intervals

(month 1, month 7, and month 12), compared to the COS of Dennis’ Patch. This

outcome was not expected as this site is directly exposed to significantly high

sedimentation levels, as well as visible and documented pollution within the Suva

Harbour.

� Species abundance was found to be similar between study sites, in terms of a

majority of similar coral species present within both study sites.

6.1.2 Coral spat Family diversity and abundance

2. To determine the recruitment rates of corals at the PIS in comparison with

corals at the control site in order to identify post-settlement resilience

properties.

� The coral recruitment rate for the PIS was interpreted from the relative abundances

of coral spat Families which were retrieved and identified every two months. On

the basis of a comparison in the number of coral spat Families identified between

study sites for every two months, it was seen that the stressed PIS demonstrated

relatively similar coral spat numbers in each coral Family, and in some instances,

higher coral spat abundances for each Family category. This interesting finding

supports the notion that the influx of an adequate supply of coral larvae into the PIS

area from neighbouring reef ecosystems is leading to the settlement of new coral

recruits and the general observed persistence of this relic reef ecosystem. It also

demonstrates that coral larvae lack the ability to distinguish between heavily

polluted habitats and cleaner sites for recruitment. The survival of larvae at both

sites remains to be evaluated in a longer term study.


143

� Coral Family diversity was recorded in the PIS and compared with the control site

through the number of coral spat Families and their relative abundances. This was

accomplished through the analysis of the settlement tiles retrieved after six months

and at the end of the study. Another interesting finding in the recruitment analysis

revealed a higher total coral spat count in the PIS compared to the COS upon

completion of twelve months of monitoring. The first eight months of monitoring

revealed higher coral spat counts in the control site for some coral Families, with

the exception of two Families which were seen to be largely predominant in the

PIS. For the twelfth month settlement tile retrieval and identification interval, the

PIS dominated coral spat abundance for all Family categories, including the

unidentifiable spat category; in comparison to the control site. It can then be

informatively stated that the diversity and abundance of coral spat recruitment

observed in the stressed PIS, is also justifiably correlated with the higher level of

coral species diversity found in in the coral cover investigation for this site in

Chapter 1.

� This monitoring study also incorporated and evaluated the influence of events

significant to the coral reef ecosystems in this study i.e. seasonality in terms of wet

and dry seasons, and coral spawning seasons. In relation to the effect of seasonality

on coral spat abundance; the total general coral spat abundance from both study

sites including all settlement tile-collection intervals, was found to be higher in the

dry season compared to the wet season. In terms of individual study site coral spat

abundance in alternate seasons, the PIS presented higher coral spat abundances in

the dry season.

� The predicted spawning times for corals in the Fiji Islands was also confirmed

throughout the aforementioned seasonal periods, as it was found that a significantly

higher percentage of coral spat from all Families were found and identified during

the “spawning season” ; a category which incorporated both the major and minor

spawning periods for corals in the Fiji Islands.


144

6.1.3 Environmental parameter magnitudes in the PIS

3. To construct a coral health Time Line at the PIS and at the COS in order to

compare and contrast the magnitudes of relevant ambient environmental

parameters.

� Daily sedimentation rates for the PIS as well as the COS were successfully

determined in terms of Average Daily Trap Collection Rate (ADTCR). It was found

that the PIS experienced higher daily sedimentation rates compared to the COS;

however, the control site did record relatively high sedimentation rates; an

occurrence which was attributed to the high current energy environment intrinsic to

the control site, and which resulted in the constant resuspension of carbonate sand

in this location. The nature of sediment observed at the PIS consisted of sediment

which was composed of mud, silt, fragments of brown algae, and also displayed a

clay-like consistency.

� Coupled with the comparatively high ADTCR seen at the PIS, the primary site also

demonstrated a significantly higher total sediment dry-weight percentage, in

comparison to the control site for the entire duration of monitoring.

� Particulate Organic Matter percentages were successfully determined for both the

PIS, as well as the control site. As was expected, the PIS presented a significantly

higher POM percentage in the water column, compared to the control site which

showed comparatively lower POM percentages. It was presumed that the December

06, 2014 sewage spill disaster in the Suva Harbour was an influential factor in the

POM result which was generated for both study sites; as increased phytoplankton

populations are typically indicative of increased nutrient concentrations and

eutrophication in the water column. In addition to this, the close proximity of the

PIS to sewage pollution sources i.e. the Suva City mainland, and documented

sewage pollution from the Nabukalou Creek outlet, places this site at a greater risk

of having an unusually high concentration of POM in the water column. This

assumption was substantiated by the significantly high amount of Particulate

Organic Matter (POM) seen in the PIS compared to the control site, along with the


145

steep increase in POM percentage seen in December 2014 and January 2015 to

February 2015 (sewage spill disaster) in this site.

In light of the significantly high POM percentages seen in the PIS, and coupled with

the significantly lower light intensity seen in this site compared to the control site

(Chapter 5), it can be stated that corals in the PIS may be periodically engaging in

POM uptake as a compensatory response for survival in low-light conditions.

Although it was determined in Chapter 5 that the primary site did receive sufficient

quantities of mean Photosynthetically Active Radiation for ensuring adequate

photosynthetic processes in coral-associated zooxanthellae.

� Light intensity was significantly lower in the PIS compared to the control site,

however, the amount of Photosynthetically Active Radiation entering the primary

site was found to be at sufficient levels in order to allow coral-associated

zooxanthellae photosynthesis and survival. The parameter of light intensity was

then excluded as a stressor variable, due to the normal magnitudes of this variable

which were observed in the primary site.

� Site water temperature was discovered to be relatively similar between sites due to

the relative proximity of each site to one another in the Suva Harbour; with mean

daily temperature in both sites not observed to be at levels conducive to coral

bleaching.

� Dissolved oxygen and salinity values were also found to be similar in range between

the PIS, and the control site; with very minor deviations in either parameter between

sites except for the month of April 2015 and June 2015 where salinity values in the

PIS plummeted to dangerously low levels. However, salinity values were seen to

stabilise to normal levels following these events in this site, and no significant

influence of this drastic drop in salinity on coral cover was observed in the PIS for

this period (Please refer to chapter 2 and the investigation into significant decreases

in coral cover seen for study sites between monitoring periods).

� In terms of dissolved oxygen values which were obtained for the PIS, no significant

fluctuation in the magnitudes of this variable was seen in this site; and which would


146

have been detrimental to coral health. Therefore, it was then concluded that the

variables of salinity and dissolved oxygen also did not exert a stressor influence on

coral cover in that of the PIS.

6.1.4 Recommendations for further study

� A more in-depth investigation into the observed persistence of reef building corals

present in the stressor-influenced PIS is needed. This study attempted to monitor

coral cover percentages and coral spat recruitment levels through successive

months in the primary site, and in the midst of sporadic exposure to various

stressors. In addition to this, an attempt to quantify the major environmental

variables was also made. These investigations need to be replicated on a larger scale

than that which was conducted for this study. Furthermore, the long term survival

of coral spat at both sites need to be monitored to determine if the apparent lack of

recognition mechanisms for healthy environments results in lower fitness for the

larvae that settles in heavily polluted sites.

� A refined investigation would involve an extensive reconnaissance dive covering

a larger area than that which was surveyed, in order to identify the presence of more

coral colonies which are very likely to be present. Additional permanent quadrats

could then be constructed in order to mark these additional newfound coral colonies

for study. It is envisaged that genetic analysis of the Suva Harbour corals in terms

of testing physiological and gene expression profiles after transplantation into

another location, be carried out in order to identify local acclimation and adaptive

responses of these corals to stressor variables.

� If spat survival proves to be similar between sites, it would prove extremely

interesting to conduct genome scans using reduced representation libraries to

determine the number of loci involved in the adaptive response to pollutants and

whether these putatively selected genomic islands are indeed responsible for the

metabolic pathways that allow corals and their zooxanthellae symbionts to thrive

under such extreme conditions.


147

� Additional control sites are also needed in order to attain a wider baseline

comparison range. Although due to budgetary, time, and resource constraints only

one control site was established and monitored; other control sites should ideally

be established at considerably farther distances from the primary site in order to

institute clear boundaries between sites, and in view of obtaining distinctive data

sets. In addition to this, water quality tests i.e. Nitrates, Phosphates, and Oil

contamination should also be conducted on a monthly basis in all sites in order to

gain insight into periodic pollution and eutrophication in the water column. Nitrate,

Phosphate, and Oil contamination tests were conducted for sites included in this

study at the start of the project; however, these tests were not continued for

subsequent months due to the excessive costs involved.

� Other important investigations such as symbiotic algal counts in selected coral

species between sites should also be conducted in order to ascertain if physiological

responses are employed by corals in the primary site to possible stressors. In this

regard, zooxanthellae layer sectioning should also be conducted in order to identify

symbiont layer thickness as another coral stress response to high sedimentation

levels.

148

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APPENDICES

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Appendix 1.0 View of Suva City and Walu Bay Industrial area from within the PIS

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Appendix 1.1 Various coral species present in the PIS

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Appendix 1.2 Reduction in coral cover from 33.65 % to 6.67% in Quadrat 4 through dredging works carried out in immediate (PIS), and photograph of dredging equipment on barge

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Appendix 1.3 Recruitment Station Rack in the PIS showing sediment film adhering onto settlement tile surfaces

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