STUDIES ON THE ECOPHYSIOLOGYOF PERIPHYTIC ALGAE

IN COCHIN ESTUARY

THESIS SUBMITTED TO

THE COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

IN PARTIAL FULFILMENT OF THE REQUIREMENTSFOR THE DEGREE

DOCTOR OF PHILOSOPHYIN

THE FACULTY OF MARINE SCIENCES

BI’

SREEKUMAR, R. M.Sc.

DEPARTMENT OF MARINE BIOLOGY.

MICROBIOLOGY AND BIOCHEMISTRY

SCHOOL OF MARINE SCIENCES

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGYCOCHIN - 682 016

DECEMBER 1996

DB1)! (fi’I’ED ‘ID

$}[?l_’lU4‘T .'49\[1) J2lJ{‘ll9\[D}L$?l‘17

CERTIFICATE

This is to certify that the thesis is an authentic record of the

research carried out by Srl. R. Sreekumar, M.Sc., under my supervision

and guidance in the Marine Biology , Microbiology and Biochemistry

Division. School of Marine Sciences, Cochin University of Science and

Technology, in partial fulfilment of the requirements for the Ph.D degree of

Cochin University of Science and Technology and no part thereof has

been presented before for any degree in any university.a at P2,::::;>-~~a

Kochi A Dr. K. J. JosephDecember, 1996. (Supervising Teacher)

DECLARATION

I hereby declare that the thesis entitled “STUDIES ON THE

ECOPHYSIOLOGY OF PEFIIPHYTIC ALGAE IN COCHIN ESTUAF|Y" is an

authentic record of research carried out by me under the supervision and

guidance of Dr.K.J.Joseph, Reader, Marine Biology Division, School of

Marine Sciences, Cochin University of Science and Technology and that

no part of it has previously formed the basis for the award of any degree.

diploma or associateship in any University.

7Kochi Sreekur11ar, R.December, 1996

ACKNOWLEDGEMENTS

I wish to express my deep sense of gratitude to my supervisingteacher, Dr. K.J. Joseph, Reader, Marine Biology Division, School of MarineSciences, Cochin University of Science and Technology for suggesting the research

problem, for inspiring guidance and constant encouragement throughout the course

of this investigation.

I am very much obliged to Prof. (Dr.) N. R. Menon. Director. School

of Marine Sciences, Cochin University of Science and Technology, who was kind

enough to provide me the necessary facilities and constant encouragement for the

study. Prof. (Dr.) R. Damodaran, Marine Biology Division has rendered useful

suggestions and discussions during the investigation. I am much grateful to him.

My unfeigned thanks to the staff members of School of MarineSciences, Cochin University of Science and Technology for their encouragement at

various stages of my work.

I thank Prof. (Dr.) Jacob Chacko, Head, Chemical OceanographyDivision and Dr. A. Mohandas, Director, School of Environmental Studies for

providing me the infrastructural facilities at their respective departments for the

completion of the work.

I express my sincere gratitude to Sri. K.K. Sivadasan, Sri. JosephGeorge and Miss. Newby Joseph, research fellows of the Marine Biology Division

for their invaluable assistance rendered during the study.

My thanks are also due to the authorities of Cochin University ofScience and Technology for providing me with all the facilities for my work.

I express my sincere gratitude to all my colleagues in the Department

of Botany , Maharaja's College, Emakulam for their wholehearted cooperation andencouragement. I am thankful to Dr. U.S. Sarma ,Director (Research), Central

Coir Research Institute, Kalavoor for his valuable suggestions.

Last but not the least I would like to thank my wife Anita Sreekumar,

who has been a source of inspiration at all times.

CONTENTS

GENERAL INTRODUCTIONIntroductionScope of the StudyReview of Literature

THE ENVIRONMENT

Geographic LocationHydrogrephic Parameters

PERIPHYTON COLONIZATIONIntroductionMaterial and MethodsResults and Discussion

Periphyton AccrualFloral CompositionPeriphyton and Hydrography

Summary

SEASONAL AND SPATIAL VARIATIONIntroductionMaterial and MethodsResults and Discussion

Qualitative DistributionQuantitative Distribution

Summary

COMMUNITY STRUCTUREIntroductionMaterial and MethodsResults and Discussion

Environmental Factors

Species Richness, Evenness, Diversity andHill Diversity numbers.Floral SimilaritySpecies CompositionPopulation Density

Summary

owco-A-s

1314

1818

18

2020222325

26262627283233

3535353838

3839394045

VII.

VIII.

PIGMENT COMPOSITIONIntroductionMaterial and MethodsResults and Discussion

Chlorophyll aTotal ChlorophyllCarotenoidsPheophytin

Summary

AUTOTROPHIC INDEXlntroductlonMaterial and MethodsResults and DiscussionSummary

PRIMARY PRODUCTIONIntroductionMaterial and MethodsResults and Dlecueslon

Gross Primary Production (GPP)Assimilation Number (AN)Community Respiration (CR)Net Daily Metabolism (NDM)Production/Respiration (P/R)

Summary

CONCLUSIONS

REFERENCES

464646484852535455

5656575862

6363646767697071

72

73

75

79

1GENERAL INTRODUCTION

Introduction

Primary producers in aquatic ecosystem assume uniquesignificance beacause of their contribution to the total organicproduction generating the fishery resources. They transform thesolar energy into potential food energy which is utilized byseveral consumers and finally made available as fish. Algae,the major primary producers in the aquatic environment comprise alarge and heterogenous assemblage of relatively simple plantssuch as phytoplankton, periphyton (haptobenthos) andherpobenthos. Among these, the role of algal plankters have beendiscussed extensively with respect to different aquaticenvironments. Major part of the published data on organicproduction pertains to this particular group. Efforts are now onto assess the specific role of other groups in primary organicproduction.

The flora on the sub-aquatic surfaces has beensubjected to very few systematic studies. Little is known oftheir geographical distribution, of seasonal cycles, relation toflow and water chemistry. The quantitative studies on this floraare scarce presumably due to the difficulties involved in theseparation of algal cells from substrata. The attached algalflora is as highly developed in running (lotic) as well as instanding waters (lentic) and form an important community of allwater bodies.

The flora forms an extremely heterogenous and complexassociation due to variability and distribution of naturalsubstrata. The terminology applied to the various algae inindividual habitats is almost as varied as the number ofinvestigations (Sladeckova, 1962; Wetzel, 1964). The assemblageof organisms living on the bottom of freshwater or brackishponds, lakes, rivers and the sea bed are termed benthic (fromGreek Bevoo = bottom). Microorganisms growing on sticks, aquaticmacrophytes and submerged surfaces are designated as periphyton(APHA, 1992). Organisms included in this group are the zooglealand filamentous bacteria, attached protozoa, rotifers, algae andthe free living microorganisms that swim, creep or lodge amongthe attached forms. The photosynthetic components include adiverse assemblage of algal forms that colonize nearly everyconceivable type of substrata available in the aquatic system.A uniform system of terminology is recommended whereby the term

periphyton includes all of the plant organisms, excluding rootedmacrophytes, growing on submerged materials in water (Wetzel andWestlake, 1974). The term periphyton has also been used for thegrowth on artificial substrata such as glass slides (Sladeckova,1960). In restricted studies of organisms on specific type ofmaterial such as rocks, macrophytes, usage of the general termperiphyton is modified by an appropriate adjective such asepilithic or epiphytic periphyton.

In general two distinict types of benthic algalassociations are logically reasonable. The haptobenthos grows on

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a solid substratum, which is usually either rock or part of anaquatic plant, though sometimes wood, animal surfaces or remainsof a man—made object, metallic, ceramic, plastic or whatever.The herpobenthos grows in or on mud which it can easilypenetrate. The term periphyton, as now used in a wide sense issynonymous with haptobenthos (Sladeckova, 1962). The plantcomponents of the aquatic system can thus be classified in towell defined groups such as phytoplankton, periphyton,herpobenthos and macrophytes. The present study is on theecophysiology of periphytic algae in Cochin estuary.

Scope of the Study

The estuaries are highly productive ecosystems andcharacteristically are more productive than the adjacent river orsea. Estuarine producers which include planktonic algae,periphyton, herpobenthos as well as macrophytes are capable ofnearly year round photosynthesis. Productivity of an environmentis mainly the contribution of various groups of autotrophicflora. Any quantitative estimation excluding any one of thesewould be an underestimation. Periphyton plays a very importantrole in the productivity of estuarine and coastal waters. It hasbeen reported that periphytic algae attain high biomass (Moss,1968; Hansson, 1988a) and may contribute up to 80% of the primary

production (Persson gt gtt, 1977); Considerable amount of workhas been done on the productivity in Cochin backwaters by differ­ent investigators (Qasim, 1973, 1979; Nair gt gtt, 1975; Gopi—nathan gt gtt, 1984). All of them have estimated the primary

_3_

production based only on phytoplankton of the estuary. Consid­ering the contribution of other autotrophic components of theestuary such as periphyton (haptobenthos), sediment flora (herpe­benthos) and macropytes, the productivity estimated by earlierauthors were essentially underestimations. The present work isan attempt inter glig to assess the contribution of periphyticflora towards the total organic production in the estuary.

Practically no work has been done on the taxonomy,seasonal and spatial variation of periphytic algae of theecosystem. An understanding of the species composition anddistribution of periphyton would give more information regardingthe richness of biodiversity of this tropical estuary.Quantitative estimation of this plant community would alsohighlight its probable contribution to the total organicproduction.

As the substrata which support periphyton are general­1y stationary , these organisms are reliable indicators ofenvironmental fluctuations. The composition and abundance ofperiphyton at a given location are governed by the water qualityat that point. Observations on periphytic growth generally arethus useful for evaluation of water quality. The autrophic index(AI) is a means of determining the trophic nature of the periphy­ton community. Normal AI values range from 50 to 200 (APHA,1992). Larger values indicate heterotrophic associations or poorwater quality. Efforts are made to find out the usefulness ofautotrophic index (AI) as a means of describing changes in

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periphyton community between sampling stations. No such studieshave been carried out in Cochin estuary earlier.

Review of Literature

Several studies have described the algal growth ofperiphytic communities both in flowing and standing waters inspite of the difficulty in the quantitative assesment of thestanding crop. The study of periphyton is often hindered by thelack of suitable natural substrata at the desired samplingstation. Furthermore, it often is difficult to collectquantitative samples from their irregular surfaces. Tocircumvent these problems artificial substrata have been used toprovide, a uniform surface type, area and orientation.In themajority of periphyton studies artificial substrata have beenused. (Sladeckova, 1962, 1972; Dumont, 1969; Rosemarin and Gelin,

1978; Loeb, 1981). The sampling of periphyton communities onartificial substratum is well established and a variety ofsampling devices have been employed (Sladeckova, 1962; Austin _t

glg, 1981). Recent studies have indicated that no singlesubstratum (whether artificial or natural) could fully representthe variety present in a stream (Siver, 1977; Lowe and Gale,1980; Eloranta, 1982). The use of artificial substrata howeversimplifies the sampling and improves replicability. But naturalperiphyton communities on aquatic macrophytes, rocks and otherpermanent structures quite often are collected for qualitativestudies. Community structure and seasonal abundance of theperiphyton of different aquatic systems of India using artificial

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and natural substrata have been studied, (Jha _t gt., 1981; Dattagt gt., 1987; Pal gt gt., 1988; Negi,1990; Tiwari,1990;Muthukumar gt gt., 1991).

Factors influencing periphyton growth

The relationship between periphytic algal growth ratesand tg gttg chemical or physical parameters was evaluated indifferent ecosystems. Several studies on agricultural streamshave found a lack of correlation between periphyton standing cropand increase in either nitrate (NO -N) or phosphate (PO - P)(Kilkus et al., 1975 ; Moore, 1977)? However, Cuker (1933) hadobserved that addition of limiting nutrients to periphytonincreases algal biomass. Fairchild and Lowe (1984) observed thatnutrient enhancement can accelerate the successional processeffecting a more rapid replacement of species. Nutrientdiffusing substrata have been used in lentic (Fairchild and Lowe,1984; Lowe _t gt., 1986; Pringle gt gttt 1986; Pringle, 1987)environments, to examine the role of various nutrients, withapparent success. Cattaneo (1987) had observed that highnutrient levels can cause a shift from communities dominated bydiatoms to communities dominated by green filaments. Physiognomyof the community often changes from being dominated by prostrateforms to dominance by large filaments. Sediment dwelling algaeare known to take up nutrients not only from water but also fromthe sediment (Carlton and Wetzel, 1988; Hansson, 1988 a, 1989)which implies less sensitivity than algal plankton. Bushong andBachmann (1989) also observed that benthic algal communities were

_6_

seldom limited by nitrogen and phosphorus. Factors limitingperiphyton accrual in east-central Illinois agricultural streamswere investigated by Munn gt _l., (1989). The investigationsrevealed that variance in the rate of chlorophyll Q accrual onsubstrata was explained through water temperature and turbiditywhereas, stream nitrate and phosphate concentrations accountedfor no significant portion of the variance.

Kilkus _t gl., (1975) reported that water temperaturewas a major driving variable for periphyton in agriculturalstreams in Iowa. Bushong and Bachmann (1989) also demonstratedthat water temperature as an important factor in controllongperiphyton growth rates.

Periphyton accumulation on artificial substrata wasfastest near the water surface and decreased repidly withincreasing depth (Eloranta, 1982). Hoagland _t gl., (1982)suggested that vertical gradients exist within a periphytoncommunity for factors such as light and nutrients. The role ofstorm events in disrupting periphyton community development has

‘also been discussed (Fisher t al., 1982).

Grazing can substantially reduce periphyton biomass(Dickman, 1968; Kehde and Wilhm, 1972). Grazed communities are

often dominated by either prostrate species, which adhere tightlyto the substrate or by small understorey species, which can avoidbeing grazed by virtue of their size (Hunter, 1980; Sumner and McIntire, 1982; Hunter and Russel—Hunter, 1983). The independent

_7_

and interactive effects of nutrient enrichment and snail grazingon structuring periphyton communities in a northern temperatelake was investigated by Marks and Lowe (1989). Grazing had amore pronounced effect on altering community composition on thenutrient enriched substrata than on unenriched substrata.Grazing caused a decrease in diversity and increase in dominanceby green algae on the nutrient enriched substrata. According toHansson (1992), a great deal of the variation in periphytonbiomass is due to variation in light and nutrient availability.

Periphyton and nutrient removal

Many lakes and streams show signs of excessivefertilization due to the input of aquatic plant nutrients fromman—related sources (Lee, 1973). Eutrophication of lakes anddrinking water reservoirs has considerable detrimental effects onthe quality of water. Several studies have been made in whichalgal growth was used either to assist in the stabilization ofuntreated sewage or for the removal of nutrients (Neel _t gl.,1961; Hemens and Stander, 1970; Pano and Middlebrooks, 1982). Asolution to the problem of separation of algae from purifiedwater is the use of periphytic algal communities on rotatingdiscs (Hemens and Stander, 1970) or in special streams or troughs(Skadovskij, 1961; Sladeckova gt gig, 1983). Experimentsconfirming that periphyton communities are useful means ofnutrient removal from polluted streams were conducted bydifferent workers (Bothwell and Jasper, 1983; Bothwell, 1983;Horner _; §l., 1983; Meier and Dilks, 1984; Vymazal, 1988).

-3­

Periphyton and fouling

The term fouling is commonly employed to distinguishthe assemblage of animals and plants which grow on artificial orman made structures, such as wood, steel, aluminium, fibre glasswhen exposed to seawater. Though algae constitute importantmembers of marine fouling community only very little has beendone on the specific role of diatoms in fouling. Hendey (1951),Round (1971), Munteanu and Maly (1981) and Huang and Boney(1983) have studied various aspects of fouling by diatoms.Slime films on paints are dominated by diatoms intermixed withbacteria, blue-green algae and dinoflagellates. All these havethe ability to produce mucilage resulting in a semi rigid jellylike matrix in which the component organisms are embedded. Thediatom Achnanthes is frequently the dominant member of slimeoccurring on antifouling surface which prevents attachment oflarger algae such as Enteromorpha (Callow gt gl., 1976). Hardy(1981) has reported the possibility of corosion caused byvarious extracellular products which come in contact with thesurfaces of structures.While describing the composition ofprimary film in the tropical marine waters of Madras, Daniel(1955) identified spores belonging to 14 different algal speciesas components of primary film in addition to diatoms.Kelkar(1989) studied the fouling diatoms from Bombay offshore andMarmagoa.

Periphyton and pollution monitoring

Periphyton has long been associated with studiesof aquatic pollution (Fjerdingstad, 1964) and a variety ofstudies have appeared concerning the structure (Cooper and wilhm,1975; Hein and Koppen, 1979; Tuchman and Blinn, 1979; Eloranta,1982) or function (Orhon, 1975; Marcus, 1980; Eloranta, 1982) ofperiphyton in polluted environments. Effects of chemicals onperiphyton structure and function also have been investigatedusing experimental ecosystems (Grolle and Kuiper, 1980; Muller,1980) to which pollutants were added. _ Species diversity ofperiphyton as an index of pollution of River Ganga was reportedby Laal _; Q1; (1982). Gaur and Kumar (1985) described algalcommunity structure in effluent holding and treatment ponds offive oil refineries. Singh and Gaur (1989) studied the changesin epilithic algal communities on introduced substrata in astream polluted with oil refinery effluent at Digboi (Assam,India). The study showed that the number of algal taxa was lessexcept blue green algae. Epilithic biomass (as chlorophyll §)also found to be considerably less at polluted stations. Thealgal community of the upstream station was markedly differentfrom the community occurring just afterthe confluence of effluents ; however, the differences weregradually reduced downstream, indicating improvement in waterquality. Effect of certain organic wastes on periphyton -levelsof the treated waters was studied by Kapur (1987). Theimportance of benthic algae growing on natural substrata and

_10_

their role in river monitoring and pollution control was reportedby Venkateswaralu _t al. (1990).

Periphyton and primary production

Members of periphyton communities are the dominantprimary producers in many lotic environments and contributesubstantially to primary production in others (wetzel, 1964.)Krock (1972) developed a test system making use of attachedmicrobial communities established on artificial substratum in the

San Francisco Bay. The communities were incubated in light/darkbottles and effects on photosynthesis and respiration of variousadded toxicants and stimulants were recorded. Orhon (1975) in asimilar study, sampled attached microbial communities in a pollu­tion gradient in Golden Horn estuary and measured the effects onphotosynthesis and respiration. Persson gt _t. (1977) had ob­served that periphyton can contribute up to 80% of the primaryproduction. Aquatic ecologists had thus became aware of theimportance of periphyton as key primary producers in lakes(Kairesalo 1980; Loeb gt _t., 1983). Primary production inagricultural streams of central Illinois was found to be limitedby temperature and light (Munn gt gt., 1989). Estimation ofprimary production with respect to periphyton was done in differ­ent ecosystems.In southern England streams, Marker (1976) re­ported primary production at the rate of 83.62 mg C m-2h—1 .Wiley gt gt. (1987) had also reported very high production inprairie river systems and subarctic streams respectively.

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Periphyton production in irrigation tanks with permanent turbidwaters was studied by Krishna Rao (1990).

The present work embodies the result of aninvestigation of periphytic algae in Cochin estuary with specialreference to its ecology and physiology. The scope of the studyand a review of literature are given in Chapter 1. An account ofthe area of study and hydrological parameters that influence thegrowth and distribution of periphytic flora are described inChapter II under the title The Environment. Chapter III dealswith the periphyton colonization in Cochin estuary and factorsinfluencing the same. Periphyton accumulation on various sub­strata is also discussed. Chapter IV is on the spatial andseasonal variation of the estuarine periphytic algae in Cochinestuary. Quantitative and qualitiative analyses of periphyticalgae at 10 different stations are discussed. Chapter V desribesthe community structure of periphytic algae in the ecosystem.Chapter VI is on the seasonal and spatial distribution of variousphotosynthetic pigments. Chapter VII deals with the role ofperiphytic algae in assessing the water quality of aquaticsystems. Chapter VIII on the productivity of the estuaryhighlights the contribution of periphytic flora towards the totalprimary production. Main conclusions of the present work arepresented in Chapter 1x.

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2THE ENVIRONMENT

Geographic Location

The locations of the present investigation includesthe backwater system running almost parallel to the Arabian Sea(90 40' — 100 l2'N, 76015‘ - 76025'E), with a total area of about300 sq.km offers an ever fluctuating environment to the flora andfauna (Fig.1). On the northern half there are two permanentpassages to the Arabian Sea, one at Cochin and the other atAzhicode. Several tributaries of the Periyar river join thebackwater at the northern half. On the southern half the riverPamba and Muvattupuzha join the system. All the rivers periodi­cally enrich the area with nutrients and considerable quantity ofsilt by flood waters. The tidal effect reaches all along thelake upto the southern end.

Three distinct tidal seasons have been observed inthis backwater, each of about four months duration. They arepre—monsoon (February to May). monsoon (June to September) and

post-monsoon (October to January).

During the monsoon showers from June to September, the

flood tides are more or less completely nullified by the freshetsand there is a strong predominance of the ebb tides. From Octob­er to January, there is a decline in rainfall and the strength offlood tide over the ebb tide is minimum. During the hot dry

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months from February to May, the flood tide effects areconsiderably accentuated over the ebb tide. This brings aboutthe changes in the salinity of the estuary. The backwater issubject to rapid changes by the incoming tides, which createturbulence in places where it opens to the sea. It is alsopolluted by industrial effluents and domestic sewage all alongits banks in the industrial belt.

Hydrographic Parameters

Salinity

The temporal variations in salinity at 10 differentstations in the estuary during the period of study are given inthe Table 2.1. The monthly mean values of salinity varied from0.3 (xl0_3) to 12.4 (xl0_3). The highest single value, 30.0(xl0—3) was recorded from station 6 during January and the low­est, 0 , from stations 1 and 7 during November and April re­spectively. Salinity distribution in the estuary is the resultof combined action of water movements induced by freshwater dis­

charge, tidal variation and mixing process. In the estuarinesystem salinity plays a dominant role in the succession of algalflora. The effect of monsoon can be seen from decreasing salini­ty gradients in the entire backwater area during the period Juneto August and a gradual rise in salinity values was observedduring the post — monsoon period. The maximum values wererecorded during the pre—monsoon months. The salinity in thenorthern part of the estuary was of higher magnitude, due to thetwo natural openings to the Arabian Sea at Cochin and Azhicode.

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Temperature

The water temperature values (Table 2.2) for entireperiod of observation are more or less in accordance with theclimatic variations. Monthly mean values varied from 24.5 to31.00 C. There was a gradual increase in temperature from Febru­ary to April followed by a fall during the monsoon. There was aslight increase in surface temperature in the entire ecosystemduring the post-monsoon period. The decline in water temperatureduring the monsoon period is not only due to the influx of fresh­water in the estuary but also the influx of cold water from thesea (Sankaranarayanan and Qasim, 1969).

Dissolved Oxygen

Seasonal variation in dissolved oxygen values atdifferent stations are shown in Table 2.3. The monthly meanvalues varied from 4.60 to 6.01 ml/1. The highest single value,7.43 ml/1, was recorded from station 3 during February and thelowest, 2.84 ml/1, from station 5 during August. The monsoon,post-monsoon and pre-monsoon values of dissolved oxygen were4.90, 5.25 and 5.38 ml/1 respectively. The seasonal values didnot vary significantly though slightly higher values are recordedduring post-monsoon and pre-monsoon periods.

Hydrogen Ion Concentration

The temporal variation in hydrogen ion concentrationat different stations are given in Table 2.4. The monthly meanpH values of the estuary varied from 6.18 to 7.67 during the

-15..

entire period of observation. The highest value, 8.70, was notedat station 10 during June and the lowest, 5.75, was recorded atstation 8 during July. Average pH values for monsoon, post­monsoon and pre—monsoon were 6.71, 7.07 and 7.75 respectively.Hydrogen ion concentration of the ecosystem is influenced bytidal fluctuations.

Silicate

The seasonal variation in silicate values at 10 dif­ferent stations is shown in the Table 2.5. The monthly meanvalues were in the range 3.65 — 25.51 mg/1 during the period ofstudy. The station 5 recorded the highest value, 57.27 mg/l,during September while the lowest, 0.85 mg/1, was obtained fromstation 9 during May. The monsoon, post-monsoon and pre—monsoon

periods recorded 17.11, 15.54 and 6.8 mg/l respectively. Heavyinflow of water leached out through various rivers into theestuary must have contributed to the higher silicate valuesduring the monsoon period.

NitriteVariation in nitrite nitrogen at different stations

are presented in the Table 2.6. The monthly mean values of

nitrite were in the range 0.31 — 2.93 Pg at/l. The monsoon,post-monsoon and pre—monsoon values of nitrite were 0.46, 1.86

and 0.71 pg at/1. Post—monsoon period recorded comparativelyhigher concentration of nitrite nitrogen. Most of the values

were within 1 pg at/1 except at a few stations.-16­

Phosphate

Table 2.7 shows the concentration of phosphate duringdifferent months at the stations studied. The monthly average

values of phosphate phosphorus varied from 0.92 to 5.48 pg at/1during the period of observation. The station 8 recorded thehighest value of 25.73 pg at/1, during May while the lowest, 0.10Pg at/1, from station 5 during February. In all, three phosphateconcentration peaks were observed in the ecosystem, one towardsSeptember and October, another in January and a third appears inMay and June. The monsoon, post-monsoon and pre—monsoon values

of phosphate were 3.10, 2.84 and 2.42 pg at/1 respectively.

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3PERIPHYTON COLONIZATION

Introduction

Periphyton, organisms on sub—aquatic surfaces, formsan extremely heterogenous and complex association. The photosyn­thetic components of these include a diverse assemblage of algalforms that colonize nearly every conceivable type of substrateavailable. Aquatic biologists have become increasingly aware ofthe importance of periphyton as key primary producers (wetzel,1964; Persson _t gly, 1977; Loeb gt gly, 1983), pollution indica­tors of water quality (Singh and Gaur, 1989; APHA, 1992. Jayapra—da and Raman , 1996) and nutrient removers from nutrient loadedwater reservoirs (Vymazal, 1988). However, study of periphytonis often hindered by lack of retrievable natural substrata at thedesired sampling station.Furthermore, it often is difficult tocollect quantitative samples from these surfaces. Hence, artifi­cal substrata have been used to provide a uniform surface type,area and orientation. The primary objective of the present studywas to explain periphytic algal growth in situ on selected arti­ficial substrata.

Material and Methods

Periphyton accrual in situ was studied on varioussubstrata such as clay tiles, rocks, wood, metal sheets, shellsof bivalves, plastic, painted surfaces and glass slides at aselected station in Cochin estuary. Thirty sets of test couponsof the above substrata in triplicate were suspended 30 cm below

-18..

water surface by means of wooden floats. Daily each set of thecoupons was pulled out with minimum disturbance and theassociated periphyton was carefully separated with knives orscrapers and collected with the help of a camel hair brush inmillipore filtered water. After preliminary observation andidentification of the live materials, samples were transferred topolythene bottles and preserved in Lugol's solution. the surfacearea of the test coupons covered by periphyton was also noted.Quantitative analysis of the periphyton was carried out using a

Sedgwick—Rafter cell and haemocytometer. 2The standing crop ofperiphyton was expressed in cell no./cm of the substratum.water samples were analysed for hydrological properties.

Salinity was estimated by Mohr-Knudsen method as described byStrickland and Parsons (1972). A SYSTRONICS-335 digital pH meter

accurate to 0.01 pH unit was used to measure pH. Dissolvedoxygen was estimated by winkler method (Strickland and Parsons,1972).Nitrite was estimated by the method described by Stricklandand Parsons (l972).Reactive phsophate estimation was made by themethod of Murphy and Riley (1962) where the extinction wasmeasured in Spectrophotometer (HITACHI 150-20) at 885 nm.Multiple regression model and Pearson's coefficient ofcorrelation (Snedecor and Cochran, 1968) was employed to find outthe effect of hydrological parameters on the colonization ofperiphyton on different substrata. The variation in periphytonaccumulation with respect to different substrate was studiedusing one-way ANOVA technique (Snedecor and Cochran, 1968).

-19..

Results and Discussion

Periphyton Accrual

The quantitative study of periphyton colonization ondifferent substrata like wood, glass, plastic, metal sheets,painted surfaces, clay tiles, granite rocks and bivalve shellsreveals (Table 3.1) that the colonization on these proceedsinitially at an exponential rate for about two weeks. On clay

3tiles, after 24 h exposure, periphytic deposit of 0.03 x 10

2cells/cm was recorded. The colonization progressed steadily

threaching the maximum on-the 13 day. Subsequently there was animmediate fall in cell concentration and remained more or lesssame. On rocky substrata the periphyton accumulation on the

3first day was 0.04 x 10 cells/cm and recorded the maximum on

ththe 10 day. The first day accrual of periphytic algae on3 3 2wooden sbustrata was 0.006 x 10 0.06 x 10 cells/cm and pro­

thceeded at an exponential rate reaching a peak on the 13 day.Plastic materials, glass slides, shells of bivalves, metal andpainted surfaces also exhibited a similar trend. The periphyticalgal biomass attained the maximum on these substrata between the10th and 14th day followed by a decline and remained more or lesssame.P1astic material showed the maximum periphyton concentration3 2 thof 12.6 x 10 cells/cm on the 14 day. Glass material, clay3 3tile, and wood accumulated about 30.2 x 10 , 19.9 x 10 and 23.73 2 thx 10 cells/cm respectively on the 13 day. Rocks,- metal andpainted surfaces showed their highest standing crop of 17.7 x3 3 3 2 th10 , 12.2 x 10 and 14.5 x 10 cells/cm respectively on the 10

-20..

day. Shells recorded their highest periphyton concentration of3 2 thabout 21.2 x 10 cells/cm on the 12 day. The substrata likeglass, wood, clay tiles and shells gathered comparatively moreperiphytic algae than others.

In all the substrata studied, periphyton colonizationshowed minor peaks without affecting the general trend . withintwo weeks all the different substrata showed their maximum pe­riphytic growth. The standing crop declined with siltation andinfestation with Balanus sp. Since all the substrata were ex­posed to identical hydrographic conditions at a particular sta­tion, the fall in cell concentration in all of them must be dueto sloughing, invertebrate infestation and grazing. The domi­nance of filamentous forms such as Mougeotia and Oscillatoria onsubstrata, after prolonged exposure, may be due to the fact thatthey are poorly grazed.

The periphyton concentration varied with substrata.This may be due to the difference in their texture. Smoothtextured surface accumulate less silt and harbour less grazersthan rough surfaced ones. The occurrence of greater periphytonconcentration on glass slides may be due to this factor. Lightis important factor limiting the periphyton colonization (Mclntire _t §lLL 1964; Gregory, 1980; Lowe gt §lLL 1986, Nair gtQLLL 1987). The exposure of substrata for less than two weeksmay result in very sparse collection and more than this periodmay result in loss of materials due to sloughing. Hence the

-21..

optimum period of accrual maxima on all substrata is between 10­14 days. The variation recorded in the rate of colonization ofperiphytic algae on the substrata studied is in agreement withthe earlier observation that distribution of periphyton isextremely heterogenous on different substrata (Cooke, 1956).

Floral Composition

Periphytic algae recorded from the differentartificial substrata during the experiment are given in the Table3.2. Most of them get dispersed in the medium due to turbulenceand remain as apparent plankton. They represent a ‘transitionalflora‘ which on the availability of substrata transform toperiphyton. Although pennate diatoms are more prone toperiphytic nature, centric diatoms like Coscinodiscus radiatus,Skeletonema costatum and Thalassiosira subtilis are also found on

the substrata whenever they are abundant in the estuary. Thepioneer species such as Navicula gracilis and Amphora angustawere present throughout the period of observation on all thesubstrata indicating their greater adherence capcity, toleranceand adaptability. Their concentration has a direct influence onthe standing crop of any substratum studied. The speciescomposition of periphyton of a given substratum often changeswith the exposure period. Certain algae recorded on a substratumdisappear at a later stage. This may either be due to grazingeffect or due to changes in the hydrographic parameters. Grazingcauses decrease in species diversity (Lubchenco, 1978). Thepresence of dominant species such as Navicula gracilis, Amphora

-22­

angusta, g; coffeaeformis, Gyrosigma scalproides, Q; spencerii,Nitzschia closterium, 3; seriata, Pleurosigma angulatum, 3;aestuarii, Surirella fastuosa of Bacillariophyceae, Mougeotia ofChlorophyceae and Oscillatoria spp. of Cyanophyceae on all thesubstrata shows that there is no substratum specificity for them.The species composition of periphyton on the substrata studied ismore or less similar as observed by Sladeckova (1962). Howeverthe occurrence of species such as Diploneis bombusy Pleurosigmanaviculaceum, Biddulphia heterocerosy Gyrosigma fasciolay Lic­mophora californica, Melosira nummuloides, fly sulcata and Masto­gloia braunii on some test coupons only may be due to the chanceassociation resulting from their smaller number. Hydrographicparameters observed at the site during the study are shown in theTable 3.3.

Periphyton and Hydrography

Correlation of periphyton with the parameters (Table3.4) such as salinity,pH, temperature, dissolved oxygen andnutrients was investigated by working out the product momentcorrelation coefficient, (r). The correlation coefficients werecomputed both for the original and log transformed values ofperiphyton concentration. The original values were found to showbetter relationship on the parameters. The periphyton values on‘tile’ was not found to be significantly correlated with any ofthe parameters. So also the values on ‘plastic’. Significantnegative correlations were observed with salinity for the

_23_

periphyton values on rock, wood, metal, painted area, shell andglass. The values on rock showed significant positivecorrelation with temperature also. Only the values on shellshowed a significant correlation with pH (negative, in thiscase). The influence of temperature on painted area cannot beruled out, though not significant. It can be seen that salinityis the most important parameter which influences, the periphytonvalues in the estuary.

Significant relationships are presented as scatterplots with the trend lines in Figs. 3.1 to 3.4.

From the multiple r square value (0.5ll7) ofperiphyton values on rock on temperature and salinity, it can beseen that about 51% of the variation in the periphyton values onrock are explained by the variations in temperature and salinity.Similarly, about 52% of the variations in the periphyton valueson shell are explained by pH and salinity, the multiple r squarevalue being 0.5202.

The variation observed in the periphyton concentrationon different artificial substrata was analysed using one—wayANOVA technique (Table 3.5). The calculated F value (0.709) is

less than the critical value for V = 7 and V2 = 104 and hence1

the difference in the periphyton concentration on differentsubstrata was not significant (ANOVA ; P < 0.01).

The study shows the suitability of different substrataand the period of exposure required to get optimum periphytic

-24­

growth. The magnitude of standing crop of periphyton on varioussubstrata is indicative of their contribution to the totalprimary production of the estuarine ecosystem.

Summary

Colonization of periphytic algae on eight differentsubstrata was studied for a period of one month. For the firsttwo weeks, the rate of colonization of periphyton was found to beexponential on all the substrata and thereafter showed aconspicuous decrease. Substrata like wood, glass and bivalveshell showed comparatively higher rate of periphyton coloniza­tion. Various species of algae recorded from the differentsubstrata consist mainly of pennate diatoms such as Naviculagracilisl Amphora anqustay Nitzschia closterium, Gyrosigma spen­cerii, QL scalproides and filamentous forms such as Mougeotiaadnata of Chlorophyceae and Oscillatoria spp. of Cyanophyceae.No substratum specificity was noted among these algae. Utilityof the different substrata and duration of exposure for thecolonization of periphyton are discussed.

-25­

Table 3.1 Periphyion colonization on different substrata3 -2(No. X10 cm )

Day Tile Rock Wood Metal Shell Plastic Painted GlassArea

1. 0.03 0.00 0.06 0.11 0.20 0.00 0.12 0.012. 0.23 0.26 0.10 0.08 0.31 0.36 0.15 0.073. 0.66 0.20 0.03 0.11 0.08 0.09 0.10 0.150. 1.75 1.27 1.60 0.62 1.12 0.51 0.70 0.515. 1.50 2.90 0.80 0.32 1.93 0.75 0.88 0.386. 6.51 2.29 9.08 1.03 2.99 0.09 0.07 0.777. 13.79 0.12 8.00 3.86 7.06 7.38 1.50 2.058. 2.02 2.73 7.88 2.28 0.06 1.90 1.03 2.089. 1.56 0.96 7.21 0.35 0.50 0.30 0.33 3.5810. 0.83 17.76 7.00 12.25 3.20 3.66 10.53 5.9211. 2.81 1.12 0.92 7.82 9.79 0.85 6.65 6.8812. 5.81 1.21 5.88 0.85 21.18 0.73 2.67 3.1113. 19.90! 0.95 23.77 9.27 7.35 9.30 8.13 30.1910. 13.39 5.08 5.11 1.38 7.20 12.57 2.51 12.0615. 10.06 1.62 11.15 3.03 6.65 1.10 1.56 f 6.0016. 6.57 0.12 5.87 0.03 2.90 2.80 1.67 I 3.6017. 0.26 0.76 0.56 0.53 0.31 0.37 0.60 0.7518. 3.80 0.80 2.78 1.10 0.00 0.70 0.08 1.3319. 2.80 0.96 1.33 0.31 0.92 0.39 0.35 1.0820. 2.00 1.30 9.01 0.20 0.00 0.80 0.56 3.1821. 2.12 2.17 1.39 0.65 1.06 3.80 0.70 2.8622. 3.60 3.59 0.51 0.07 2.27 3.80 1.13 2.1123. 2.09 7.71 5.00 0.50 3.52 3.99 1.07 1.6720. 1.78 1.05 0.87 0.69 0.51 0.66 0.56 0.2125. 2.20 5.10 2.80 3.33 1.80 1.77 1.35 9.7826. 3.52 0.07 2.51 2.75 2.36 1.57 1.23 6.2227. 6.83 1.30 2.02 1.50 3.22 1.12 1.02 2.9128. 8.61 0.36 2.20 0.70 0.16 0.05 1.58 0.98329. 2.75 6.88 0.77 3.62 6.27 2.57 3.88 7.11

Table 3.2 - Periphytic algae observed on different substrata

Amphora angusta Greg.A. coffeaeformis Kutz.Biddulphia pulchella Gray.B. laevis Ehr.B. rhombus w.Sm.Coscinodiscus radiatus Ehr.Diploneis bombus Ehr.D. elliptica (Kutz) Cleve.Fragilaria oceanica Cleve.Gyrosigma balticum (Ehr.)Cleve.G. fasciola Ehr.G. scalproides Rab.C. spencerii W. Sm.Licmophora flabellataAgardh Mastogloia brauniiGrun.Melosira nummuloidesAgardh.Navicula gracilis Ehr.N. notabilis Grev.Nitzschia closteriumw. Sm. N. longissima(Breb) Ralfs.N. obtusa W. Sm.N. panduriformis Greg.N. seriata Cleve.N. sigma w.Sm.Pleurosigma angulatumw.Sm. P. acuminatum Gran.P. aestuarii w.Sm.P. falx Mann.P. naviculaceum Breb.Skeletonema costatumSurirella fastuosa Ehr.Thalassiosira subtilisGran.Triceratium reticulatumEhr.Tropidoneis lepidopteraCleve.Mougeotia adnata Iyengar.Oscillatoria spp.

I |++l |++I+|+|++

+|+|I+|++++|+ +l+l

+ I

I |++|

l|++++|+| +|++

+ +++|

I l++I

I ++++

+ +I+++++++++|

SubstrataP G+ ++ ++ _+ _+ +— +— ++ ++ _.+ ++ ++ ++ _

+ ++ +

— ++ ++ ++ ++ ++ +— ++ _+ —+ ++ .­+ +

+ +

||+|+|++

+ l+++

+|+|+++++++l+ +++|

|l++++++

I |+++

I +l+l

+|+|l++++++|

+ |+++

I +l+l

ll+++|

+

+

(W — Wood, M — Metal, S —Granite, T — Tile,Absent)

Shell, P — Plastic,PA - Painted surface, .+,

G — Glass,Present I

Table 3.3 — Hydrographic parameters

Day Salinity pH Do Nitrite Phosphate Temp.0(%o) (ml/1) pg at/1 pg at/1 ( C)

1 27.5 7.86 4.76 2.01 9 16 30 52 24.0 7.95 5.57 12.02 9 04 31 53 27.0 7 84 4.76 4.12 6 12 31 04 24.5 7.76 4.08 2.04 3 24 31 05 26.5 7.88 3.80 3.23 2 57 31 06 27.0 7.87 3.94 3.01 7 08 31 07 25.0 7.67 5.26 2.14 8 11 31 58 24.0 7.83 3.86 4.28 6 07 31 09 22.5 7.97 4.76 3.26 9 42 31 510 17.5 7.86 4.08 2.02 11 64 32.011 21.5 7.56 6.12 3.00 8.29 31 212 21.0 7.65 3.40 2.31 11 20 30.513 17.5 7.81 3.91 2.12 6 10 30 114 25.8 7.82 4.09 3.20 4 02 30 015 21.5 7.52 4.27 2.20 3 18 30 016 15.5 7.46 6.12 1.02 4 22 29 517 15.0 7.51 4.21 1.28 3 04 29 018 12.8 7.41 5.71 5.08 2 67 29 219 13.5 7.39 6.12 5.22 4 24 29 520 12.0 7.36 6.23 1.08 11 56 30.221 17.5 7.56 5.90 2.15 5 70 30 022 15.2 7.50 3.86 3.26 4 64 30.523 12.4 7.49 6.70 4.40 6 04 30 524 12.8 7.51 5.90 1.48 2 14 30.925 11.5 7.47 4.91 2.07 2 20 30 526 18.6 7.67 5.22 3.12 4 16 30 227 24.3 7.82 4.60 3.07 3 87 30 528 33.3 8.03 5.81 5.28 3 01 30 529 14.7 7.56 6.21 5.02 5 26 30 8

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cocoa.” onomH.u «Hood. «n~¢o.u nmflnn. ¢nonn.- m~.mo.- ~nm~a.- Ao-~.u omooo.n ~mnm~.- ooqmo.- -meo. oenn~.u =N

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.Hmm ma . ~o.mm«n muuh

nuouoflnumm amuwwoaouuan m zouxnmfluum uo uwuuma coaumauuuou w.m OHDMB

Table 3.5 ­substrataANOVA of periphyton concentration on different

Bet. samples 149525536.00within samples 3134668544.00

DF MS

7 21360790.00104 30141044.00111Total 3284l94048.00

SS - Some of SquaresMS - Mean SquareDF - Degree of Freedom

Salinity on Painted areaPerlphyton In thousands

16

14‘

15 17 19 21 23 _ 26 27 29Salinity in ppt

Salinity on GlassPerlphyton In thousands

35

30

25

15 17 19 21 23 I 25 27 29Salinity in ppt

F18. 3.1 Scatter plots with the trend lines

Salinity on Wood

5 Perlphyton In thousande

20

15 17 19 21 23 25 27Salinity In ppt

Salinity on MetalPerlphyton In thouaainde

14

15 17 19 21 23 25 27Salinity In ppt

Fig. 3.2 Scatter plots with the trend lines

Salinity on ShellPerlphyton In thousands

5

I20

15 17 19 21 2a 25 27 29Salinity In ppt

Salinity on Rock

0 Perlphyton In Thousands

15

15 17 19 21 23 25 27 29Salinity in ppt

Fig. 3.3 Scatter plots with the trend lines

Ternparature on RockPurlphyton In Thouannda

O

15 7

10 _ /w~/£ //6 - /,/"J"

/..-F",-*1 ­/x3./'O r’ l 1 r 1 1 ' - 1 ‘ I30 30.5 31 31.5 32 32.5 33 33.5 34

Temperature degree 0

PH on Shell5 P°|'|Ph¥ton In thousands

W­

20

O I ' 1 I 1 1 I n J u7.5 7.55 7.6 7.65 77 775 73 735 79 795. , _ _ _ _ 8Fi . 3.4 .8 Scatter P10tS Wlth the trend lines

4SEASONAL AND SPATIAL VARIATION

Introduction

Periphytic algae growing on stones, aquatic macrophytesand other submerged objects are useful in assessing the role ofpollutants in the ecology of lakes, streams and estuaries(Sladeckova, 1962). They also effectively influence the produc­tivity of any aquatic environment. In shallow waters the majorgroups of autotrophs are algal plankton, periphyton, sedimentmicroflora and macrophytes.Although information on various as­pects of algal plankton and their role in the productivity ofCochin estuary is available (George, 1958; Qasim gt §lL, 1969,1972; Gopinathan, 1972; Joseph and Pillai, 1975), information onperiphytic algae and other autotrophs from Cochin backwater iswanting. Present study was undertaken to gather information onthe qualitative and quantitative distribution of periphytic floraof the ecosystem.

Material and Methods

Ten locations (1-5, south of Cochin barmouth, 6-10north of Cochin barmouth) from the backwater were surveyed forqualitative and quantitative distribution of periphytic algaeduring 1993-94. Periphytic algae from these locations werecollected by using plain 25 by 75 mm glass slides (APHA, 1992).

At least three replicate slides mounted on woodenfloats were suspended 30 cm below the water surface. Samples

-25­

were collected fortnightly by pulling out the slides causingminimum disturbance. The associated periphyton was carefullyscraped using scalpel and camel hair brush in millipore filteredwater. After preliminary observations and identification of thelive material, samples were transferred to polythene bottles andpreserved in Lugo1‘s solution. The algal forms were identifiedby consulting the standard and recent publications (Subramanyan,1946; Desikachary, 1959; Randhawa, 1959; Hendey, 1964;Philipose, 1967; Gonzalves, 1981; Gopinathan, 1975, 1984; JinDexiang gt al., 1985).

Scrapings from the slides were dispersed in suitablevolume of preservative with vigorous shaking. Quantitativeestimation of periphyton was done using a Sedgwick—Rafter cell.Periphyton concentration was expressed as number of cells persquare centimeter of substrate area, calculated as follows:

2Cells/cm slide surface =Cells/ml suspended scrapings x total volume of scrapings

area of slide, cm

Results and Discussion

The periphytic flora of Cochin backwater comprised 66species of diatoms, 8 of Chlorophyceae and 2 of Cyanophyceae(Table 4.1). Nearly 86% of periphytic algae belonged toBacillariophyceae. Out of these, 7 genera and 9 species belongedto centrales and 24 genera and 57 species to pennales. The

-27­

dominant species among the centrales were Melosira nummuloides,Biddulphia laevis and Thalassiosira subtilis and pennales wereNavicula gracilis, Amphora anqusta, A. coffeaeformis pleurosigmaacuminatum, E; aestuarii, Gyrosigma spencerii, Q; ggglpggiggg,Nitzschia closterium, N. obtusa and Achnanthes brevipes. Speciesof Navicula and Pleurosigma were recorded from almost all thestations studied. The Chlorophyceae comprised of 8 speciesconsisting about 11% of the periphytic flora. The dominant amongthem were Mougeotia adnata and Spirogyra jogensis. Blue greenalgae were represented only by two genera ie. Oscillatoria andMerismopedia. The former being recorded from all the locationssurveyed.

Qualitative Distribution

Among the 29 species of periphytic algae reported fromstation 1, 21 species were observed in monsoon, 17 in post­monsoon and 13 in pre-monsoon. Navicula gracilis, N. notabilis,Gyrosigma spencerii, Pinnularia interrupta and Mougeotia adnatadominated during monsoon Gyrosigma spencerii, Navicula gracilis

and Oscillatoria spp. were present in greater numbers during thepost—monsoon while Navicula gracilis, Nitzschia obtusa and ELseriata dominated during pre-monsoon. At stn.2 twenty sevenspecies were observed during the period of study. Of theseNavicula gracilis, Climacosphenia moniligera, Gomphonemalanceolatum, Nitzschia obtusa, 3; sigmoidea and Oscillatoria spp.were observed in all seasons. The total number of speciesrecorded at stns. 3, 4 and 5 were 30, 34 and 32 respectively.

-28..

Navicula gracilis, Pleurosigma aestuarii, Thalassiosira subtilis,Oscillatoria spp. were the dominant forms found in thesestations. Stns. 6 and 7 recorded 34 species each. Naviculagracilis and Oscillatoria app. were very common in both thestations. In addition to these, species such as Amphora angusta,Pleurosigma aestuarii and Nitzschia closterium were also present

in large numbers. The lowest number of species was reported atstn.8. Out of the 25 species observed, Navicula gracilis,Amphora ccffeaeformis, Achnanthes brevipes, Eungtogramma sp. and

Navicula bicapitata were present throughout the period of study.The green alga, Stigeoclonium flagelliferum, was reported onlyfrom this station. The number of species observed at stns. 9 and10 were 26 and 32 respectively. Navicula qracilis, Gyrosigmaspencerii and Mougeotia adnata were commonly distributed in thesestations. Navicula capitata was observed in significant numbersthroughout the period at stn.10.

Analysis of algal species observed at differentstations during monsoon, post—monsoon and pre—monsoon revealed

that some are found only during monsoon and a few in pre­monsoon. 30 species were observed throughout the yearirrespective of the seasonal changes in the estuary. These wereAchnanthes brevipes, Amphora angusta, A.coffeaeformisClimacosphenia moniligera, Diploneis elliptica, D.subova1is,Egggtggggmmg sp, Gomphonema lanceolatum, Gyrosigma scalproides,

Qyrosigma spencerii, Navicula bicapitata, N.capitata, Nggracilis,N.hasta, Nitzschia closterium, N.obtusa, fig seriata, N.sigma,

-29­

N.sigmoidea, Pinnularia interrupta, P.braunii, Pleurosigmaacuminatum, EL aestuarii, EL naviculaceum, Surirella fastuosa,Synedra ulna, Terpsinae musica, Thalassiosira subtilis, Mougeotiaadnata and Oscillatoria spp. 15 species, Amphora ostreareaBiddulphia laevis, g; rhombus, Caloneis brevis, Campylodiscusecheneis, Gomphonema sphaerophorum, Navicula plicata, Nitzschialongissima, Mastogloia braunii, Surirella tenera, Closteriumacerosum, Cosmarium contractum, Q; pyramidatum, Spirogyrajogensis and Stigeoclonium flagelliferum were reported atdifferent stations only during monsoon period. Achnanthescoarctata, Coscinodiscus radiatus, Gyrosigma balticum, Q; macrum,Hantzschia amphioxys, Nitzschia vermicularis, Triceratiumreticulatum were reported only during the pre—monsoon period indifferent parts of the backwater.

Owing to the mixing of waters in the Cochin backwaterfrom the major rivers and to the banking of water during floodtides from the Arabian Sea, the periphytic algae was found to becomposite in character. There was continuous fluctuation in tur­bidity, salinity and temperature of water in the ecosystemthroughout the year. Periphyton at all the stations consistedmainly of diatoms. Next to diatoms, green algae were thedominant flora during certain seasons especially at stations1,2,7 and 8. The blue—green algae, though present at allstations were not so conspicuous as the diatoms and green algae.Oscillatoria was the only genus of this group in almost all thestations surveyed. In Table 4.2—1l, averages of the relative

_30_

abundance of total periphyton and its component groups of algae,viz. the diatoms, the green and the blue green algae at differentstations during monsoon, post— monsoon and pre—monsoon for oneyear are given. Forms observed at stations 1 and 2 were more orless of the same quality, though differing in quantity. The twostations being away from the opening to the sea , the periphyticalgae consisted mainly of freshwater and euryhaline forms. Atstations 5, 6, 9 and 10, which are near to the mouth of theestuary marine and brackishwater forms predominated. A fewfreshwater forms were also observed in these stations but duringmonsoon season only.

The Bacillariophyceae were the major component in theperiphytic algae at all times in the estuary. The percentagecomposition of species representing Bacillariophyceae,Chlorophyceae and Cyanophyceae were 86%, 11% and 3% respectively.

Most of the green-algal members of periphyton flora were observedduring monsoon, their standing crop being comparatively less inother seasons. This clearly shows that they are recruited to thebackwater through the major rivers discharging freshwater intothe ecosystem. However, Mougeotia adnata was present in most ofthe stations and throughout the period of study indicating itstypical estuarine adaptability. Oscillatoria among Cyanophyceaeis the only genus widely distributed throughout the year in theestuary as periphyton. Though relatively less in number andspecies composition than the diatoms and green algae, this groupwas present at all stations.

-31­

Quantitative Distribution

The monthly mean values of periphyton cell concentra­tion at 10 different stations are shown in the Table 4.12. Thehighest value of 31576 cells/cmz was reported from stn. 4during February while the lowest 1430 cells/cmz from Njarackalduring December. Monthly average cell concentration for theestuary varied from 9817 cells/cmz in October to 16288cells/cmz in January. The annual mean periphytic algal cellconcentration of different stations showed that it varied from9625 cells/cmz to 18907 cells/cmz. Stn.1 recorded the maximumannual mean cell concentration while stn. 8 recorded the lowest.Southern stations of the estuary in general recorded higher cellconcentration than northern stations. Seasonal variation in thestanding crop (Table 4.13) showed that the post-monsoon hadhigher cell concentration. The seasonal mean values of satandingcrop for monsoon, post—monsoon and pre—monsoon periods were13454, 13576 and 13229 cells/cmz respectively. Comparativelylower values of standing crop were recorded from Stations 2 and8. Turbulence of water at stn. 2 due to the confluence of one ofthe tributories of Muvattupuzha River with the backwater may beresponsible for the low periphyton standing crop. The toxiccomponent of industrial effluents from factories such as FACT,TCC and Cominco Binani were discharged into one of thetributories of Periyar River. Stn. 8 is located near itsconfluence with the backwater on the northern side. Incidentlythe lowest annual mean value of standing crop was recorded fromthis station.

-32­

Temporal and spatial variation in periphytic algalcell concentration was analysed (Table 4.14) using a 2-way ANOVA.

A significant variation in standing crop occurred among thedifferent stations (ANOVA; P <0.05) in the estuary. Asignificant difference was observed in the monthly values ofstanding crop in all the stations (ANOVA; P < 0.05).

The seasonal averages of periphpyton concentrationshowed that post—monsoon season had a greater cell concentrationthan monsoon or pre—monsoon. During south west monsoon (June­September) freshwater forms were recruited into the estuary.Stns. 1 and 2 showed dominance of these forms especially duringmonsoon. The post—monsoon flora comprised mainly of euryhalinespecies. Stations located near the barmouth showed the presenceof many stenohaline forms especially during pre—monsoon. Thestudy revealed remarkable species diversity in the periphyticflora of Cochin backwater which formed a significant autotrophiccomponent of the ecosystem . The mangnitude of standing crop(Table 4.12) is indicative of their contribution to the totalprimary production.

Summary

The floral composition of periphyton in Cochinbackwater from June 1993 to May 1994 were studied usingartificial substrata. The floral composition depends on therecruitment of freshwater forms through the rivers and marineforms through the flood tides of Arabian Sea. Periphytic flora

-33­

in Cochin backwater comprised 66 species of Bacillariophyceae, 8of Chlorophyceae and 2 of Cyanophyceae.

A significant variation was observed in the spatialand temporal distribution of standing crop of periphytic algae,3 4 2the range being 5.9 X 10 to 1.8 X 10 cells /cm .The monthly3 4mean values for the estuary varied from 9.8 X 10 to 1.6 X 10

2cells / cm .

The magnitude of standing crop observed at variousstations is indicative of its role in the primary productivity ofthe estuary.

-34­

Table 4.1 Periphytic flora in Cochin estuary

Baclllarlophyceae

Achruanfhes brevipes Agardh.A. coarcrala Berb.Amphora angusra Greg.A. coffeaelormis Kulz.A. osfrearea Breb.Biddulphia pulchella Gray.5. Iaevis Ehr.

B. rhombus (Ehr.) W. Sm.Calerreis brevis Ehr.

C. permagnn (Bail) CleveCampylodiscus ochenais Ehr.Coscinodiscus niridus Greg.C. radialus Ehr.Climacosphenia moniligera Ehr.Cymbella marina CaslracaneDiploneis bombus Ehr.D. elliplica (Kulz) Cleve.D. subovalis Cleve.Eunalogramma sp.Eunotia diodon Ehr.Fragilaria oceanica Cleve.Gomphonema Ianceolalum Kulz.G. sphaerophorum Ehr.Grarnmalophora marina (Lyngb.) Kulz.

Gyrosigma balricum (Ehr.) Cleve.G. lasciola Ehr.G. macrum W. Sm.G. sralproides Rab.G. spencerii W. Srn.Hanlzschia amphioxys (Ehr.)Licmophora flabellara (Grev.) Agardh.Maslogloia braunii Grun.Melosira nummuloides (Bory) Agardh.Navicula bicapirala Lagersledt.N. capifala Ehr.N. gracilis Ehr.N. hasfa Panlocsek.N. hennedyei Cleve.N. norabilis Grev.N. p/icala Donk.N. pusilla W. Sm.Nilzschia closterium (Ehr) W. Srn.

N. Iongissima (Breb.) Flalls' N. obrusa W. Sm.

N. panduriformis Greg.. N. serials Cleve.

N. sigma W. Sm.N. sigmoidea (Ehr.) W. Sm.N. varmicularis (Kutz.) Hanlzsch.Okedenia inflexa Breb.Pinnularia braunii (Grun.) Cleve.P. inlerrupla W. Sm.Pleurasigma acuminalum (Kulz) Grun.

' P. éngularum W. Srn.P. distorlum W. Srn.P. aesluarii W. Srn.P. falx Mann.P. naviculaceum Breb.

Slrialella unipunctafa Agardh.Surirella fasluosa Ehr.

S. fenera Greg.Synedra ulna Ehr.Terpsinae mus/"ca Ehr.

Ylralassiosim sublilis (Oslenleld) Gran.Triceralium reliculalum Ehr.

Tropidoneis lepidoplera (Greg) Clev.

Chlorophyceae

Chlarella conglomerate (OIL)Closlerium acerosum Ehr.Cosmarium contradum Kutz.C. pyramidarurn Greg.Mougeolia adnala Iyengar.Oedogonium rtrlescens Willrock.Spirogyra jogensis lyengar.Sligeoclonium flagel/i/erum KuLz.

Cyanophyceae

Merismopedia elegans A. Braun.OsciI!aIon'a spp.

Table 4.2 Seasonal variation of periphytic flora at stn.1

Algal forms Monsoon Post­monsoon

Achnanthes brevipesAmphora angustaBidulphia laevisClimacosphenia moniligeraCoscinodiscus nitidusGomphonema sphaerophorumGyrosigma balticumG.macrumG.sca1priodesG.spenceriiNavicula bicapitataN. capitataN. gracilisN. notabilisNitzschia longissimaN. obtusaN.seriataN.sigmaPinnularia interruptaPleurosigma acuminatumP.aestuariiStriatella unipunctataSynedra ulnaThalassiosira subtilisClosterium acerosumCosmarium pyramidatumMougeotia adnataSpirogyra jogensisOscillatoria sp.

6105

4750

3418

*Ce11 numbers per cm

Table 4.4 Seasonal variation of periphytic flora at stn. 3

Pre­Monsoon

r—-b-|--\oa:~lO'\U1u>(.uNI—­ fqpaou o - u o o 0 n o

Achnanthes brevipesAmphora angustaA. coffeaeformisBiddulphia laevisCaloneis brevisCampylodiscus echeneisClimacosphenia moniligeraEunatogramma sp.Eunotia diodonGomphonema sphaerophorumGrammatophora marinaMelosira nummuloidesNavicula capitataN.graci1isNitzschia closteriumN.obtusaN.sigmaN.sigmoideaN.vermicu1arisPinnularia brauniiP.interruptaPleurosigma acuminatumP.aestuariiSurirella fastuosaSynedra ulnaTerpsinae musicaThalassiosira subtilisMougeotia adnataSpirogyra jogensisOscillatoria sp.

15068

940

#2798200150600269

53

*Ce11 numbers per cm

Table 4.5 - Seasonal variation of peripytic flora at stn. 4

S1. Algal forms Monsoon Pre- Post­No. monsoon monsoon1. Achnanthes brevipes #18 2218 4092. Amphora angusta 218 230 2223. A.coffeaeformis ---— ---— 2544. Biddulphia laevis 333 ---— ---—5 Caloneis brevis 300 ---— ---­6. Climacosphenia moniligera ---— 1566 20157. Diploneis bombus ---— 45 ---­8. D.e11iptica 18 120 1589. Gomphonema sphaerophorum ---— 43 ---­10. Gyrosigma balticum ---— 884 87211. G.macrum ---— 320 24712. G.sca1proides 738 590 86713. G.spencerii 304 1083 290414. Melosira nummuloides ---— ---— 24515. Navicula capitata 37 ---— 8016. N.graci1is 3897 2541 202817. Nitzschia obtusa 1470 960 ---­18. N.seriata 1726 132 ---­19. N.sigma 368 ---— 31720. N. sigmoidea 170 ---— ---­21. Pinnularia braunii ---— 120 ---—22. Pleurosigma acuminatum 37 318 ---—23. P. angulatum ---— ---— 57524. P. aestuarii 870 322 51525. P.navicu1aceum 230 400 16526. Striatella unipunctata ---— 50 ---—27. Surirella fastuosa 248 600 44728. Synedra ulna 205 ---— ---­29. Terpsinae musica 1287 435 15630. Thalassiosira subtilis 2100 305 24531. Closterium acerosum ---— 58 ---—32. Mougeotia adnata 2373 950 ---­33. Spirogyra jogensis 1706 ---— ---­34. Oscillatoria sp. 3043 856 1383

Total 21696 15146 141042

*Ce11 numbers per cm

Table 4.6 — Seasonal variation of periphytic flora at stn. 5

\O®\lU'\U1II-‘-Lc.lI\Jb-t

Achnanthes brevipesAmphora angustaA. ostreareaCaloneis brevisCoscinodiscus radiatusClimacosphenia moniligeraCymbella marinaFragilaria oceanicaGomphonema sphaerophorumGyrosigma macrumG. scalproidesG. spenceriiNavicula gracilisN. hastaN. hennedyeiN. plicataNitzschia closteriumN. obstusaN. seriataPinnularia interruptaPleurosigma acuminatumP. aestuariiP. naviculaceumStriatella unipunctataSurirella fastuosaS. teneraSynedra ulnaThalassiosira subtilisTriceratium reticulatumMougeotia adnataSpirogyra jogensisOscillatoria sp.

210

38

68

325315

32724002040

255917

1945640

1005300

625937793505

2190

1875

360

305220

2203

Cell numbers per cm

Table 4.7 - Seasonal variation of periphytic flora at stan. 6

Monsoon Postmonsoon

Premonsoon

232

29.

Achnanthes brevipesA. coarctataAmphora angustaA. coffeaeformisBiddulphia laevisCaloneis brevisDiploneis subovalisEunatogramma sp.Fragilaria oceanicaGomphonema sphaerophorumGyrosigma scalproidesG. spenceriiHantzschia amphioxysLicmophora flabellataMelosira nummuloidesNaviecula gracilisN. hastaNitzschia closteriumN. obtusaN. seriataN. sigmaOkedenia inflexaPinnularia brauniiPleurosigma acuminatumP. angulatumP. aestuariiP naviculaceumSurirella fastuosaS. teneraTerpsinae musicaThalassiosira subtilisCosmarium pyramidatumMougeotia adnataOscillatoria sp.

390

621

720117

1581093

B25541133

1000

400

1950450188657

105240815170

365390

1073140685895

200288

1321355

4001060

4568160

1314

200

700

160210

325190

600

Cell numbers per cm

Table 4.8 - Seasonal variation of periphytic flora at stn. 7

Post Premonsoon

\Om\l0'\LJ'lrbhJI\)r-I U I I I I

v-o--r-o­ LAN;-O

14.

Nv--I-o-r-r­ O\om~lU\U‘I

IQ I-1

22:

MN Aw

NNNN m\lO\U'l

Achnanthes brevipesAmphora angustaA. coffeaeformisA. ostreareaCaloneis brevisDiploneis subovalisEunatogramma sp.Eunotia diodonGomphonema lanceolatumG. sphaerophorumGyrosigma scalpriodesG. spenceriiMelosira nummuloidesNavicula bicapitataN. gracilisN. hennedyeiNitzshcia closteriumN. longissimaN. obtusaN. panduriformisN. seriataOkedenia inflexaPinnularia brauniiP. interruptaPleurosigma acuminatumThalassiosira subtilisChlorella conglomerataClosterium acerosumCosmarium contractumC. pyramidatumMougeotia adnataOedogonium rufescensSpirogyra jogensisOscillatoria sp.

Cell numbers per cm

Table 4.9 - Seasonal variation of periphytic flora at stn. 8

S1. Algal forms Monsoon Post— Pre­No. monsoon monsoon1. Achnanthes brevipes ---~ —--— 382. Amphora angusta —--— 468 —-—­3. A. coffeaeformis 20 94 3254. Biddulphia rhombus 160 —--— —-—­5. Cymbella marina —--— 30 -—-­6. Diploneis subovalis 80 —--— —-—­7. Eunatogramma sp. 1244 247 13958. Eunotia diodon —--— 32 —-—­9. Gomphonema lanceolatum 610 —--— 25510. Gyrosigma scalproides —--— 185 —--­11. Navicula bicapitata 240 _50 59512. N. gracilis 700 1000 95813. N. hasta —--— 717 —-—­14. Nitzschia longissima 505 40 F———15. N. seriata -—~— 765 1916. N. sigmoidea —--— —--— 27517. Pnnularia interrupta —--— 50 19018. Synedra ulna —--— 117 11519. Tropidoneis lepidoptera —--— 795 24520. Chlorella conglomerate - - — - — - - - -- 37721. Cosmarium contractum — — — - — — — — -— 24022. Mougeotia adnata —-——— 188 —-———23. Oedogonium rufescens —-——- 2858 16224. Stigeoclonium flagelliferum 595 —--— —--­25. Oscillatoria sp. 439 351 118

Total 4593 7987 53072

Cell numbers per cm

Table 4.10 - Seasonal variation of periphytic flora at stn. 9

S1. Algal forms Monsoon Post PreNo, monsoon monsoon1. Achnathes brevipes 1714 —--— 2502. A. coarctata -——- 1120 9553. Amphora angusta -——- 708 3204. A. coffeaeformis 1053 240 1805. Diploneis subovalis —--— 130 —--­6. Eunatogramma sp 312 —--— ——-­7. Fragilaria oceanica -——- 170 —--—8. Gomphonema sphaeorphorum 440 577 ——-­9. Gyrosigma scalproides 244 82 -——­10. G. spencerii 2916 143 41511. Melosira nummuloides ——-—— -——- 74512. Navicula gracilis 190 3260 164613. N. hasta -——- 160 20514. Nitzschia closterium —___ —--— 18515. N. obtusa 2293 1015 —--—16. N. seriata —--— 92 34017. Pleurosigma acuminatum 1528 -——- -——­18. P. angulatum —--— —--— 42019. P. falx —--— 55 5520. Surirella fastuosa -——- 60 5621. Synedra ulna 22 249 -——­22. Thalassiosira subtilis 25 145 -——­23. Chlorella conglomerata -——- 170 52524. Cosmarium pyramidatum -——- 105 —--—25. Mougeotia adnata 1447 31 116326. Osicllatoria sp. -——- 350 370

T0ta1 12184 8862 78312

Cell numbers per cm

Table 4.11 - Seasonal variation of periphytic flora at stn 10.

S1. Algal forms Monsoon Post PreNo. monsoon monsoon1. Achnanthes brevipes 750 1519 15172. A. coaretata -——— -——— 9953. Amphora angusta -——— -——— 4124. A. coffeaformis 130 -——— 2205. Biddulphia pulchella -——— 255 -——­6. Campylodiscus echeneis 290 -——— -——­7. Diploneis subovalis 832 208 -——­8. Eunatogramma sp. -——— -——— -——­9. Fragilaria oceanica ---- 370 -——­10. Gomphonema lanceolatum 118 180 -——­11. Gyrosigma scalproides -——— 392 -——­12. G. spencerii 533 480 143013. Mastogloia braunii 250 -——— ---—14. Melosira nummuloides -——— 1365 79015. Navicula bicapitata 475 -——— -——­16. N. capitata 2756 700 66817. N. gracilis 863 720 131718. N. hasta -——— 300 95019. N. notabilis -——— 467 ---­20. N. plicata -——— 120 20521. Nitzschia longissima 68 95 -——­22. N. obtusa 1575 625 -———23. N. seriata 1705 1170 -———24. N sigma -——— 1125. 11525. N. sigmoidea -——— ---- 64726. Pinnularia interrupta -——— -——— 155027. Pleurosigma acuminatum 75 370 -——­28. P. aestuarii 70 130 52529. P. angulatum -——— 220 37530. Thalassiosira subtilis -——— -——— 92531. Mougeotia adnata 500 875 200032. Osicillatoria sp. 2287 713 1293

Total 13227 12399 159902

Cell numbers per cm

Table 4.12 - Monthly mean values of periphytic algal cell numbers

at stations 1-10

18416

15930

20065

14090

6880

10125

10000

2510

5660

14410

16416

9162

24376

2910

12047

18357

2644

4920

2391

17000

15240

11447

29439

7834

9320

7720

23900

7875

19290

15010

Stn Monsoon Post-monsoonNo. ----------------------------------------------------------------------- -­

JUN JUL AUG SEPT OCT NOV DEC JAN FEB

1. 20160 16230 19037 29897 11806 12933 24694 14984 22998

2. 12540 4010 15380 16760 13360 10728 18838 28597 20890

3. 3622 3750 4040 12960 2848 8798 27259 28209 83054. 21824 16085 27023 21830 8872 20700 16330 14672 31576

5. 21226 4768 21020 16650 14790 23418 13650 8653 7580

6. 8380 12990 14670 12126 11492 16370 9260 17793 12000

7. 18749 20750 12322 9095 13437 10847 6620 16043 18934

3. 6013 1740 2700 7920 5904 14742 3800 7501 59209. 11994 9142 13540 14060 10668 8958 1430 14390 398410. 18100 17852 8143 9000 5000 10107 22448 12040 17540

Avg 14260 10731 13787 15029 9817 13760 14432 16288 14972

........... _.E.._...._...._...._....._..._._.._._..._._____...._...__.__....__..._.values per cm

Table 4.13 — Periphytic algal cell numbers(Seasonal Average) in the Cochin backwater

Stations Monsoon fest-monsoon Pre—monsoon

1. Vaikom 21336 16108 192772. Murinjapuzha 12174 17886 143613. Panavally 6094 16781 205474. Vaduthala 21696 15146 141045. Kumbalam 15917 15128 89576. Bolghatty 12042 13731 120517. Chitoor 15230 11736 138708. Eloor 4593 7987 53079. Narackal 12184 8862 783110.Karuthedom 13277 12399 15990

Average 13454 13576 132292

Values per cm

Table 4.14 - Analysisspatial)

Source SSBet.Co1s 519598912.Bet.Rows 1557626880.

Error 4100001024.

Total 6177226752

of variance of standing crop (temporal and

DF MS F00 11 47236264.00 1 14100 9 173069648.00 4 17900 99 4l414152.0000 119

5COMMUNITY STRUCTURE

Introduction

Investigations on periphytic algae in Cochin estuary(Sreekumar and Joseph, 1995a, 1995b, 1996) have gatheredinformation regarding the floral composition, seasonal andspatial variation, and factors influencing periphytic growth. Avariety of studies have appeared concerning the structure (Cooperand Wilhm, 1975; Hein and Koppen, 1979: Eloranta, 1982 ) orfunction (Orhon, 1975; Marcus, 1980) of periphytons in differentecosystems. Efforts were also made to relate the changes in theperiphyton community structure with the level of pollutants usingintroduced substrata (Cooper and wilhm, 1975; Singh and Gaur,1989). Various diversity indices, similarity index and biomassof periphytic algal community are often used for monitoringpollution levels. Richness, evenness, diversity and similarityindices, which are essential for understanding communitystructure are dealt with reference to the periphytic algae inCochin backwater.

Material and Methods

Periphyton samples for the qualitative andquantitative study were collected from 10 different locations(Fig.1) in Cochin estuary. Detailed method of collection (APHA,1992) and identification were described in chapter IV.Hydrographical parameters such as salinity, dissolved oxygen andnutrients such as nitrite, phosphate and silicate were determinedfollowing the standard methods (Strickland and Parsons, 1972)

-35­

Diversity Indices:—

Species diversity may be thought of as being composedof two components (Ludwig and Reynolds, 1988). The first is thenumber of species in the community, which the ecologists referto as species richness. The second component is speciesevenness or equitability. Eveness refers how the speciesabundances (number of individuals, biomass cover etc.) aredistributed among the species. Diversity indices incorporateboth species richness and evenness into a single value. Thesame diversity index value can be obtained for a community withlow richness and high evenness as for a community of highrichness and low evenness.

Richness Index

Species richness was calculated according to Margalef's(1958) formula.

S-1R = ———-­

ln (n)where R = Species richness

S = Total number of species in the communityn = Total number of individuals in the community

Evenness Index

Species evenness was worked out according to Sheldon (1969)e H’

E = ———-­

where E Evenness indexIeH Hillsdiversity no.

S = Total number of species in the community.

Diversity Index

Diversity indices incorporate both species richnessand evenness into a single value. Computation of speciesdiversity in periphytic algae was made using Shannon—Weaver index(Pielou, 1975)

where H‘ Diversity index5 u Total number of individuals in the communityni Total number of individuals in a species

Similarity Index

Similarity index is a simple and elegant measure ofcomparing stations for obtaining an integrated picture of thebiotopes and calculated using Sorensen's (1948) equation :

2cS = ————— —— x 100

a + b

where 'c' = The number of species common at both stations and'a' is the number of species at one station and 'b' is thespecies at the other station. S = index of similarity.

_37_

Results and DiscussionEnvironmental Factors

Environmental parameters such as salinity, temp.,pH and dissolved oxygen and nutrients such as silicate, nitriteand phosphate were studied (Table 5.1). water temperature rangedfrom 26.3 to 30.l0C. Monthly variation in salinity was in therange from 0.12 to 14.07 x 10-3. Generally salinity showed adecreasing trend from barmouth (station 6) to station 1, towardssouth and station 8, towards north (1 < 2 < 3 < 4 < 5 < 6 > 7 >8). Salinity at stations 9 and 10 were similar to that ofstation 6 because of their proximity to the second permanentopening of the backwater into the sea. A decline in salinity atall stations was noticed during south—west monsoon (June —September). A steady increase in salinity was found during post­monsoon (October - January) and the highest being recorded duringpre-monsoon (February — May) period. Dissolved oxygenconcentration of water ranged from 4.63 to 5.85 ml. 1-1. The pHof water ranged from 6.24 to 7.73. The lowest monthly\mean valueof silicate (3.01 mg.l_1) was noted in May and the highest (27.37mg.l-1) in September. The mean values of nitrite and phosphate

ranged between 0.34 and 2.25 ug at. 1-1 and 0.93 and 6.23 ugat.l respectively.

Species Richness, Diversity, Evenness and Hill's DiversityNumber­

The pattern of diversity (Table 5.2) indices showedvarying trends at different stations studied. In general

-33­

diversity indices showed comparatively higher values duringmonsoon and post—monsoon periods than those in pre-monsoon. The

maximum R (Margalef, 1958) value (2.38) was at station 4 duringpost—monsoon and the minimum (1.06) at station 8 during post­monsoon. The maximum H'(Shannon-weaver index ) value (2.88) was

at station 6 during post-monsoon and the minimum (1.76) at sta­tion I in the pre—monsoon period. Similarly the maximum N(Hill's diversity number) value (17.93) was recorded during pre­monsoon period at station 6 while the minimum (5.84) during pre­monsoon period at station 1. These clearly show the abundanceand high diversity of species during monsoon and post—monsoonperiods. No significant seasonal variation was observed in thecase of E (eveness or equitability) values.

Floral SimilarityFloral similarity was measured using ‘trellis diagram’

by pooling the total number of species over a period of one yearat one station with another (Fig. 5.1). The abundance ofAchnanthes brevipes, Amphora angusta, Q. coffeaeformis, Gyrosiqma

scalproides, g; spencerii, Navicula gracilis, Nitzschia obtusayN.seriata, 3; closterium, 5; sigma, Pleurosigma aestuarii, E;accuminatum, Surirella fastuosa, Synedra ulna and Thalassiosirasubtilis at the stations studied accounted for the similaritybetween stations.

Species Composition

Periphytic flora of Cochin backwater comprised 66species of Bacillariophyceae, 8 of Chlorophyceae and 2 of

-39­

Cyanophyceae (Table 5.3). The number of species recorded at 10stations varied from 25-34. The maximum number of species (34)

was reported at stations 4,6 and 7 while the minimum (25) wasnoted at stn.8.

Population DensityMonthly occurrence and abundance of periphyton

standing crop at 10 stations are given in Fig 5.2. The averageperiphyton cell numbers in the estuary varied from 9.8 x 103 to1.6 x 104 cells/cmz. The highest standing crop (4.1 x 104 ) wasreported from station 4 during February and the lowest (1.4 x 103 cells/cmz) from station 9 during December.

Correlation of periphytic algal biomass with theenvrionmental parameters such as salinity, dissolved oxygen,temperature, pH, silicate, nitrite and phosphate was investigatedby working out the correlation coefficient (r) (Table 5.4).Though salinity is one of the most fluctuating factors, no sig­nificant relationship with periphyton standing crop was observedexcept in station 3 . In general, though there was no significantcorrelation between periphyton and dissolved oxygen, significantpositive correlation was observed at station 8. This station isapparently polluted due to its proximity to effluents from thenearby industrial concerns. Freshwater influx during monsoonremoves toxic materials and increases the concentration of thedissolved oxygen. This facilitated the higher periphytonaccrual during monsoon at this station. Temperature showed asignificant positive correlation at station 3 while pH values

-40­

showed a negative correlation with perihyton at station 5. Theseresults are in agreement with the earlier studies (Sreekumar andJoseph,l995a) in the ecosystem. Though significant correlationbetween periphyton and nitrite was not observed in general, atstation 8 a significant positive correlation was observed.Phosphate values did not seem to act as limiting factor forperiphyton in this estuary.

Several studies on agricultural streams have foundlack of positive correlation between periphyton biomass andeither nitrate or phosphate (Kilkus et al., 1975; Moore, 1977).Similar results were obtained in this study also.Periphytic algaeare known to take up nutrients from both water and sediment whichgot adhered to the substrata (Carlton and wetzel, 1988; Hansson,1988a). Hence they are not as sensitive as phytoplankton tonutrients in water. Moreover different seasons of the estuaryare characterised by typical flora , response of which varieswith species. The monsoon season is dominated by freshwaterforms whereas premonsoon is dominated by stenohaline species.It is during the post—monsoon season, that the typical estuarineflora (euryhaline) flourish well. Incidently higher periphyticbiomass was recorded during the post—monsoon season. The averageperiphyton cell numbers for monsoon, post—monsoon and pre—monsoon

were 1.34 x 104, 1.35 x 104cm and 1.32 x 104 cm -2 respectively.It is the qualitative variation induced by recruitment ofriverine and marine flora that render the standing crop more orless uniform.

-41­

In Cochin backwater, the species diversity ofperiphytic algae was comparatively low. In Vellar estuary(south—east coast of India), Rajan gt gig (1987) had reportedhigher values of species diversity index (3.37—4.73) of benthicdiatoms. Similarly, a higher species diversity index ranging from3.35 to 4.26 was reported in Mississipi salt marsh (Sullivan,1978). However, diversity index values reported (Joseph andSreekumar, 1993) for the phytoplankters of the estuary duringpre-monsoon, monsoon and post—monsoon were 2.6, 2.1 and 2.2respectively. Periphytic alage in most of the stations showedslightly higher values of diversity index than phytoplanktonexcept for the pre-monsoon season.

Earlier studies (Boesch, 1972; Rajan _t gig, 1987) forbenthic diatoms had shown that the maximum H'value coincided with

the occurrence of the maximum number of benthic diatom species.Stations 6 and 10 that showed higher values of H’ during post—monsoon season recorded abundance of benthic diatoms (30 species)also.

There was considerable variation in the values ofevenness index (E) at different stations during the period ofstudy. The lowest value (0.38) was at station 3 during the post­monsoon and the highest value (0.82) was observed at station 8during the monsooon. Wide variation in the evenness index mustbe due to the impact of ever fluctuating estuarine environment onperiphyton distribution. However, the mean values of evennessindex for the pre—monsoon, monsoon and post—monsoon periods wcre

-42_

0.60, 0.67 and 0.61 respectively. Evenness index (E) is theresult of competiton under optimum conditions or may be aresponse to unfavourable conditions (Patrick, 1971). Both thesefactors appear to hold good in this case. Monsoonal flushinginto the estuary causes nutrient enrichment and depletion ofnutrients occur as the rains subside in the succeeding months.

It is to be noted that Amphora angustay Gyrosigmaspenceriiy Navicula gracilis, Nitzschia obtusa, Pleurosigmaaestuarii, Thalassiosira subtilis, Mougeotia adnatay Oscillatoriaspp. were dominant throughout the year in most of the stationsstudied. Despite the variations in different parts of theestuary, the common occurrence of these species throughoutindicates that they are the typical euryhaline species of thistropical estuary.

Composition of the periphytic flora in Cochin estuary(Table 4.1) shows that out of 40 genera present, 31 belong toBacillariophyceae while Chlorophyceae is represented by 7 generaand Cyanophyceae by two genera. Sixty six species of diatomsbelonging to 31 genera form the dominant group of periphyticalgae in the estuary. Among the 66 species, pennate diatoms arerepresented by 57 species and centric by 9 species. Species suchas Gomphonema lanceolatum, G.sphaerophorum, Nitzschia sigmoidea,

Pinnularia interrupta, P.braunii, Spirogyra jogensis, Cosmariumcontractum, Q; pyramidatum, Closterium acerosumy Oedogoniumggfgsggng showed their highest standing crop during the monsoonperiod and at freshwater stations. The fact that these species

-43­

decreased in number during the post—monsoon period indicated that

they are freshwater froms and their tolerance to salinity islimited.

Although information on periphytic algae is meagre,the available data on Indian waters and that of elsewhere in theworld indicate that diatoms form the dominant autotrophiccomponent. The present study is also in agreement with thegeneral trend. The fact that the diatoms form the dominant groupof periphytic algae in the estuary shows that they are welladapted for this particular estuarine environment. Compared to

centric diatoms, pennate diatoms which have mucilage pads forattachment are more in number in periphyton samples. Among thegreen and blue-green algae those having mucilage sheaths andrhizoidal cells occur as periphyton. The coexistence of variousdiatoms in the periphyton community is made possible owing to theadaptability and euryhalinity of species, while the essentialrequirements are not limited in the estuarine envrionment.However, grazing does occur but it is offset by the faster rateof multiplication among diatoms. All these favour diatoms to bethe dominant periphytic algae. Moreover, unlike the filamentousor more elaborate green and blue-green algae, smaller size ofdiatoms offer less resistance to water currents in the estuarinesystem.

-44_

Summary

The average periphyton cell numbers for monsoon, post­monsoon and pre—monsoon were 1.34 x 10 4, 1.35 x 104 and 1.32 x

10 4 per cm2 respectively. Though the standing crop at differentstations exhibited considerable variation with salinity ,this isnot reflected in the average values of the estuary as a whole.Butthe individual values of standing crops varied from 9.8 x10 3 to1.6 x 10 4 cells / cmz

At stn.3, the standing crop showed significant positivecorrelation with salinity, one of the most fluctuatinghydrographic parameters. At other locations the correlationbetween standing crop and salinity was not significant. Thevariation in the relationship can be attributed to the type offlora characteristic of space or seasons. Different parts of theestuary showed the dominance of freshwater, euryhaline or stenc­haline forms depending on their proximity to river mouth or sea.Among the 40 genera and 76 species of periphytic algae, thediatoms comprise 31 genera and 66 species. The number of speciesrecorded at different stations varied from 25-34. Diversityindex of periphytic algae was slightly higher than that of plank­tonic algae of the backwater. Similarity indices of periphyticflora at majority of stations studied were generally < 60 indi­cating the extent of its diversity.

_45_

Table 5.1 Monthly mean values of environmental parameters

Month salinity Diss.oxygen Temp. pH Silicate NO -N P0 -P2 4-3 -1 0 -1 -1 -1(x10 ) (ml 1 ) ( C) (mg 1 ) (Pg at 1 )(pg at.1 )

June 0.35 5.10 26.4 7.20 10.59 0.74 3.02July 0.12 5.07 26.3 6.87 11.54 0.34 2.26Aug. 1.61 4.63 27.4 6.24 19.97 0.51 2.23Sep. 0.58 5.30 27.8 6.94 27.37 0.74 6.23Oct. 0.38 5.08 28.0 6.83 14.03 1.03 6.01Nov. 0.21 5.07 28.8 6.95 15.16 1.17 1.61Dec. 8.78 5.06 28.6 7.43 5.77 2.21 1.67Jan. 13.47 5.15 28.0 7.39 25.40 2.25 5.89Feb. 13.80 5.06 30.10 7.55 8.46 0.54 0.93Mar. 14.07 4.85 29.5 7.48 7.51 0.71 1.70Apr. 11.84 5.05 29.6 7.47 7.09 0.87 2.43

Table 5.2 Diversity indices of species richness (R), diversity (H), evenness

(E) and Hill's Diversity number (N).

1 1.21 1.76 0.44 5.84 2.00 2.57 0.62 13.11 1.65 2.35 0.61 10.502 1.56 2.32 0.64 10.27 1.38 2.40 0.79 11.09 2.14 2.72 0.69 15.22

4 1.88 2.34 0.52 10.48 2.10 2.51 0.56 12.36 2.38 2.71 0.62 15.035 1.97 2.72 0.80 15.24 1.96 2.59 0.66 13.38 1.66 2.38 0.64 10.906 1.59 2.16 0.54 8.75 1.70 2.39 0.64 10.99 2.30 2.88 0.77 17.937 1.57 2.25 0.59 9.52 2.07 2.33 0.49 10.33 2.34 2.79 0.71 16.44

9 1.53 2.16 0.54 8.67 1.16 2.03 0.63 7.67 2.09 2.23 0.46 9.3010 1.75 2.69 0.82 14.87 1.68 2.262 0.81 13.78 2.22 2.83 0.77 17.09

Table 5.3 List of periphytic algae occurring in Cochin estuary

Algal genera Number of speciesStations

BacillariophyceaeAchnanthesAmphoraBiddulphiaCaloneisCampylodiscusCoscinodiscusClimacospheniaCymbellaDiploneisEunatogrammaEunotiaFragilariaGomphonemaGrammatophoraGyrosigmaHantzschiaLicmophoraMastogloiaMelosiraNaviculaNitzschiaOkedeniaPinnulariaPleurosigmaStriatellaSurirellaSynedraTerpsinaeThalassiosiraTriceratiumTropidoneisChlorophyceaeChlorellaCloateriumCosmariumMougeotiaOedogoniumSpirogyraStigeocloniumCyanophyceaeMerismopedia — 1 — — —Oscillatoria — 1 1 1 1 1 2 1 1 1

I I-II-II-I

I I I-ml II-I-NH I I

IIII-I-I II-II--I

In-II-I-I-l\.IH

INII-I ||I-I-I-Iv--INr—­

I I I I

IAINII II-ltull III-I-II-I-I I-bll-II ILLJII-‘D-‘I IPUIIUII-‘I-‘I-‘I II-II-In-I-I--I-I IN!»-I-II-I-I INII-I-alt-I--I

III-Ir-II-NI-I»:-I:-II III-Ir-av--IN»-loot-II-I III-I-I-I--INl\JI(.nI'~.Ir-I III-I-I-I--I-J:-I-I-hrur-I II-II--I-I\.)I-ha)-I(.nJob|l ||._a...|N|.;:s—-I-uhrur-Ir-I-NI»-I--II-'r-‘I III-II I I II-‘IUD-U'ILA.II-‘I

I--I I II-I |I-IILAJLAJII

lIHIHHIwIIwNH| II H II I Iuaw ILHGWH “I

II-II-HI--I

I

Ir-II--II II-II-II-I II-II-I

II-r-I

table 5.4 Correlation coefficient (I value) betaeen periphytie algae nnd_environmental paranetera

Station Saianity Dissolved Temperature pH Silicate N0 -N P0 -Poxygen 2 ‘1 0.2600 20.0294 -0.1695 0.3544 0.1253 0.0201 0.1692

2 0.3101 0.2001 0.415 -0.1059 0.2901 -0.4605 -0.2000

3 IIO.1093 0.4312 10.6614 0.4932 -0.3990 0.1699 0.3936

4 0.1631 -0.0564 0.1990 -0.1004 0.0016 -0.4111 -0.0055

5 -0.3645 -0.1162 -0.1500 -0.5962 0.3000 0.2011 0.2044

6 -0.0651 -0.3133 0.1452 -0.1044 0.2501 -0.4230 -0.3151

1 -0.0059 -0.0564 -0.2263 -0.0031 0.4526 0.2544 0.1151

0 -0.1091 I0.6105 0.3900 0.2214 0.1501 10.5779 0.3559

9 0.1045 0.0126 0.5161 0.0965 -0.0115 -0.5431 0.1151

10 0.2055 0.3100 0.2241 0.4041 -0.6006 0.3622 -0.5190

I Significant at 51 level (P < 0.05)

In Significant at 11 leve (P < 0.01)

Degree of ireedon = 11

1 2 3 4 5 6 7 8 9 1o44.4 50.9 59.0

59'6 59°° 55-2 45-9 57.6 56.6 57,5

67.6 58.1 58.5 42_3 52.6 54.0

64-5 55.9 37.2 56,7

64-5 42.8 59.6

37.2 75.7

64.4 63.3

60——77%

Fig. 5.1 Trellis diagram showing floral similarity at 10 stations.

_ZZZ§ZZ%ZZZ2

522222252522222

22222222222222222222222222222222222222222222

22533222QEZZZZ5322

mod x

.o:vmomu

0ZHDZ¢Hm

MONTHS

Fig.5.2 Monthly mean values of periphyton standing crop at stations 1­

6PIGMEN T COMPOSITION

Introduction

Cochin backwater has been studied extensively withregard to the various groups of planktonic algae (George, 1958;Qasim et al., 1969, 1972; Gopinathan, 1972; Gopinathan et al.,1984; Nair et gly, 1975; Joseph and Sreekumar, 1993). However,information on periphytic algae, growing on stones, aquaticmacrophytes and other submerged objects is scanty. Periphytoncolonization on different substrata, floral composition of theperiphyton community, its spatial and temporal variation in theestuary have been studied (Sreekumar and Joseph, 1995 a, 1995 b).Periphyton has a significant role in the primary production andinfluence the ecology of water bodies. Seasonal and spatialvariations in pigment composition of periphytic algae in theestuarine complex are presented in view of their importance inprimary production.

Material and Methods

Quantitative determination of the pigments was doneusing periphyton growth on glass slides of 25/75 mm size keptsubmerged at different stations (APHA, 1992). Pigments wereextracted with aqueous acetone and OD measured with aspectrophotometer (Hitachi 150-20). Individual glass slidesretrieved from different stations were placed directly into 100ml of a mixture of 90% aqueous acetone and 10% saturated MgCO

3-46­

solution. The samples were frozen in the field andokept steepedin acetone for 24 h in the dark at or near 4 C. 3 ml ofclarified extract was transferred to a 1 cm cuvette andabsorbance read at 750, 665, 645, 630, 510 & 480 nm. Theconcentration of chlorophyll ‘a’, ‘b', ‘g’ and carotenoids werecalculated using the equations given in Strickland and Parsons(1972).

C = Chlorophyll Q = 20.7 E -4.34 E -4.42 Eb 6450 6650 6300C = Chlorophyll 9 = 55 E -4.64 E — 16.3 Ec 6300 6650 6450C = Carotenoids = 7.6 (E — 1.49 E )p 4800 5100where E is the absorbance at the respective wave lengths. Eachextinction was corrected for a small turbidity blank bysubtracting the 750 nm reading.

The chlorophylls and Carotenoids were estimated in2

mg/m using the formula (APHA, 1992) :

C x volume of extract, L

area of substrate, m

where C , and C and C are respective C values of chl.Q, chl.gb c pand carotenoids.For the estimation of active chlorophyll Q andpheophytin Q, the procedure was similar to that of chlorophyllsas given above. The extinction of the extract was measured at665 and 750 nm. Each 750 nm reading was subtracted from the

-47­

corresponding 665 nm extinction and using the corrected valueschlorophyll Q and pheophytin Q concentration per unit surfacearea of sample was calculated as follows:

26.7 (665 -665 ) x v2

Chlorophyll §,mg/m = ——————————————————— -­

area of substrate, m

26.7{1.7(665 ) - 665 } x v

pheophytin a, mg/m = -------------------------- -­area of substrate, m

Where: 665 = extinction at 665 nm before acidificationb

665a

extinction at 665 nm after acidification

v = volume of extract, L,

The value 26.7 is the absorbance correction and 1.7 is theabsorption-peak—ratio.

Results and Discussion

Chlorophyll Q

The seasonal and spatial variations of chl.§ are shownin Table 6.1. The annual mean concentration of chl.§ in theestuary was 50.80 mg/m2. During monsoon period the mean chl.§value was 58.14 mg/m2 whereas pre—monsoon and post-monsoonvalues were 47.49 and 46.77 mg/m2 respectively. The highestconcentration of chl.g (214.20 mg/m2) in the estuary was recorded

2at Panavally in September whereas the lowest (10.26 mg/m ) fromMurinjapuzha during July. Chl.§ values are generally taken as a

-48­

measure of standing crop in any ecosystem. The concentration ofch1.g at different stations highlighted the magnitude of periphy­ton biomass and its role in the ecosystem. The seasonal varia­tion in the chl.g values indicated that monsoon period was moresuitable for periphytic growth in the estuary than either pre­monsoon or post-monsoon. The lowering of salinity due to heavyrains and inflow of freshwater from various rivers into theestuary might have facilitated the growth of both freshwater andeuryhaline forms.

Singh and Gaur (1989) reported ch1.§ concentrations of2

53.08, 34.58 and 49.34 mg/m for periphyton in a stream polluted‘with oil refinery effluent at Digboi (Assam, India) in April,1986, September, 1986 and January, 1987 respectively. However,Hansson (1992) had reported 30-270 mg/m2 in Swedish Lakes and 20­

400 mg/m2 in Antarctic Lakes. Joseph and Pillai (1975) reportedseasonal and spatial variation in chl.g values for the plankto­nic algae in Cochin estuary. For the plankton, ch1.§ values werethe lowest during monsoon and highest during post-monsoon. Theannual contribution of chl.a by the sediment microflora of theestuary is estimated to be 70.35 mg/m2 with the incidence ofhigher values during both pre—monsoon and monsoon (Sivadasan and

Joseph, 1995). But periphytic chl.g showed the maximum concen­tration during monsoon season.

Seasonal and spatial variations in the concentration ofchl.g were examined using a two way ANOVA (Table 6.2).Significant difference in chl.a values was observed between

-49­

different stations as well as months. (ANOVA; P<0.01). Correla­tion between the monthly mean values of ch1.a and hydrologicalparameters such as salinity, temperature, dissolved oxygen, pH,silicate, nitrite and phosphate of the estuary was analysed(Table 6.3). No significant correlation between chlorophyll Qand hydrological parameters was observed. However, correlationanalysis at different stations revealed that there is negativecorrelation between chl.a and salinity in locations near rivermouths and positive correlation in stations with saline condi­tions. Hence salinity could be one of the factors influencingits distribution in the estuary.

Productivity of an ecosystem is a function of thestanding crop which is often expressed as ch1.a concentration.The richness of ch1.§ of the periphytic flora indicated theextent to which this autotrophic component influencedproductivity of the estuary. The annual mean value of primaryproduction estimated based on phytoplankton alone was clearly anunderestimation.Thus the necessity of a correction factor forperiphyton production is imperative for a more realisticestimation of primary productivity.

Chl.b concentration showed wide variations fromstation to station (Table 6.4). It varied from zero at a few

2stations during pre-monsoon to 51.98 mg/m at Vaikom duringSeptember. The mean values of ch1.b in the estuary duringmonsoon, post—monsoon and pre-monsoon were 11.08, 4.54 and 3.54

2mg/m respectively while the annual mean concentration was 6.36

-50­

2mg/m . The concentration of ch1.Q being directly related to thegreen algal biomass, comparatively higher values of it duringmonsoon season indicated its luxuriant growth during the period.Heavy rains during monsoon lowered the salinity in the estuaryfavouring the growth of freshwater green algae such as Mougeotia,Spirogyra, Closterium, Oedogonium and Stigeoclonium. The south­ern stations of the estuary showed higher values of chl.b thanthe northern stations. Incidentally southern region receivedmore freshwater from rivers in addition to the usual monsoonprecipitation.

Vaikom, the southernmost station studied recorded themaximum concentration of ch1.b during monsoon season. Salinityhere was very low (< 1 x 10-3) throughout the year. Compared tothe values of chl.g, ch1.b values were very low except in a fewstations during monsoon months. During the monsoon season, thebackwater maintained more or less freshwater conditions butsalinity increased gradually through the post-monsoon andreaching the maximum during pre-monsoon. However, the chl.bvalues were maximum during monsoon and gradually decreased during

the post-monsoon and reaching the lowest during pre-monsoon. Aninverse relationship between chl.b and salinity values was evi­dent in the estuary.

The ratio of chl.§ to chl.§ (Table 6.5) showedtemporal variation from 0.03 (March) to 0.21 (September). Valuesare comparatively low to that reported for phytoplankton inVellar estuary (0.54) by Vijayalakshmy in 1986. Chl.b/chl.§

-51­

ratios for monsoon, post—monsoon and pre—monsoon wer 0.19, 0.11

and 0.07 respectively. The annual mean value was 0.12 whereasthe same for chl.g was 0.25 indicating the dominance of diatomsamong the periphytic flora (Table 4.1).

Monthly mean values of chl.c (Table 6.6) showed anirregular pattern of distribution with an annual mean value of12.59 mg/m2 in the estuary. The lowest value recorded in theecosystem was 1.24 mg/m2 at Vaduthala during October and thehighest (60.55 mg/m2) also at the same place in September. Themonsoon, post—monsoon and pre—monsoon values of chl.g were 12.66,

9.13 and 15.98 mg/m2 respectively. Unlike ch1.§ and chl.Q, themaximum concentration of chl.g was observed during pre—monsoon

season. with the increasing salinity in the estuary, there was acorresponding increase in the diatom standing crop as indicatedby the higher values of chl.g during pre—monsoon. The ratio ofchl.g to chl.a (Table 6.5) in the estuary was fluctuating and wasless than unity throughout the year. This ratio showed thephysiological state of the standing crop (Bhargava and Dwivedi,1976) and for a healthy crop it is less than unity. Qasim andReddy (1967) observed a similar fluctuation in the chl.g to chl.gratio for phytoplankton population of the same ecosystem.

Total Chlorophyll

Distribution of total chlorophyll (a+b+c) was similarto ch1.g the both being maximum in September and minimum inOctober in most of the stations (Fig. 6.1). Annual mean value of

-52­

2total chl. was 69.75 mg/m with monsoon, post-monsoon and pre­monsoon showing 81.88, 60.44 and 66.93 mg/m2 respectively.The concentration of chlorophyll is indicative of the floralcomposition (Gopinathan gt gly, 1984). The estuary recorded anannual mean of 50.80 mg/m2 of chl.g during the period of study

indicating the presence of a fairly good quantity of periphytonstanding crop throughout the year. Chl.b and chl.; arecharacteristic of green algae and diatoms respectively. Theannual mean concentration of chl.§ was 6.36 mg/m2 and that ofchl.g was 12.59 mg/m2. This comparatively higher value of chl.gshowed that the dominant periphytic flora of the estuarycomprised mainly of diatoms . This was evident from the floralcomposition of the estuary (Table 4.1). Diatoms formed 86.9%where as green algae and blue green algae comprised 10.5% and2.6% respectively. Thus the pigment concentration agree wellwith the composition of periphytic flora.

Carotenoids

Monthly variation of carotenoids are given in Table6.7.The maximum concentration of carotenoids was recorded in

September as in the case of chl.g, chl.Q and chl.g. The valueswere, in general, higher during the monsoon period and decreasedgradually during the post-monsoon and pre-monsoon periods.Annual mean values of carotenoids for different stations such as

Vaikom, Murinjapuzha, Panavally, Vaduthala, Kumbalam, Bolghatty,Chittoor, Eloor, Njarackal and Karuthedom were 21.76, 8.44,26.47, 12.29, 6.50, 13.92, 17.00, 25.03, 15.23 and 16.17 mg/m2

-53­

respectively.Eloor station recorded the highest value (80.39mg/m2) in November. Stations which recorded higher values ofchl.§ showed higher values of carotenoids also. The carotenoidvalues of periphytic flora were relatively low when compared tothe sediment flora (microbenthos) in this estuarine system(Sivadasan & Joseph, 1995). The ratio of caroteniods to chl.g(Table 6.5) was also fluctuating and were always less than unitythroughout the year.

Pheophytin

Pheophytin concentration of periphyton in the estuary(Table 6.8) was the highest (16.04 mg/m ) during monsoon followed

2

by a gradual decrease during post-monsoon (11.97 mg/m ) and pre­2

monsoon (8.78 mg/m ). The incidence of high pheophytin must bedue to the high turbidity of the estuarine water resulting fromthe greater inflow of freshwater from various rivers in theecosystem. Turbidity affected light penetration which led to afaster rate of conversion of chlorophyll to pheophytin. This wasevident from the higher values of pheophytin at stations locatedat river mouths. Eloor (10.28 mg/m ) Chittoor (9.85 mg/m2) andNjarackal (11.89 mg/m2) are located near confluence of Periyarriver and the estuary while Murinjapuzha (10.34 mg/m2) and Pana­vally (23.98 mg/m2) are situated near the Muvattupuzha rivermouth. The upstream station, Vaikom (20.24 mg/m2), is situatednear the Thanneermukkam barrage opening. The ratio of pheophytinto chl.a (Table 6.5) varied from 0.16 to 0.33 with 0.28, 0.27 and

-54­

0.19 for the monsoon, post-monsoon and pre-monsoon periods re­spectively.

Summary

The annual mean chl.Q content of periphyton estimatedfor the estuary is 50.80 mg/m2. The very high values of chl.Qrecorded from different stations signify the role of periphytonsin the ecology of Cochin backwaters. The seasonal averages ofchlorophyll concentration show that the pigment production isslightly more during the monsoon (58.14 mg/m ). Monthly values(mean) of chlorophyll at different stations revealed that thereis significant spatial and temporal variation in its distribution(2 way ANOVA:P <0.01). The annual mean values of chl.b and chl.Q

concentration were 6.36 and 12.59 mg/m2 respectively. Thesevalues confirm the floral composition of periphytic algaedescribed in chapter V.

The annual mean corotenoid content of periphyton2

estimated to be 16.28 mg/m . The ratio of chl.b chl Q andcarotene to chl Q was always less than unity. Pheophytin Qconcentration for the monsoon, post-monsoon and pre-monsoonperiods were 16.14, 119.97 and 8.78 mg/m2 respectively. Therewas a gradual decrease in pheophytin Q concentration during thepost-monsoon period. Increased turbulence and low light penetra­tion during the monsoon may be responsible for the higherpheophytin Q concentration during the post-monsoon period. In­creased turbulence and low light penetration during the monsoonmay be responsible for the higher pheophytin Q concentration.

-55­

iphyton

Table 6.1. Seasonal variation of chlorophyll 3 content of per

Cochin estuary.

at.different stations 1n

Post-monsoon

Pre-monsoon

Monsoon

Stn.

May

Apr.

Mar.

Feb.

Jan.

Dec.

Nov.

Oct

Sew.

Aug.

July

Jun.

No. 1. 93.98 66.60 77.7 91.43 62.53 69.42 34.9% 62.53 68.46 66.76

0‘,­CU

'1'—.p

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3.63

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19.26 67.66

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55.33 46.00 43.77

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49.54

;\.'v'E . Values in mg m

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ucmucou m aH>nn0LnH£u cm

Apr may

Mar

Feb

Jan

Dec

Nov

Oct

Aug

Jul

Jun

Pigments

9.97 9.9: 9.99 9.19

_0.07 0.06

0.18 0.11

0.21

0.16

0.20

.18

Ch1.§

Ch1.Q

0.38

0.39

0.26

0.30

0.17

0.20

0.30 0.15

0.24

0.15

0.24

0.23

Chi.

Ch1.g

0.22

0.27

0.33

_9.:1

0.24

0.23

0.38

0.35

9.35. 9.4;

0.36

0.30

: Ch1.§

Carotenolds

0.20 0.17 0.16

V9.21

0.20

0.25

0.33 0.25

0.28

0.30

: Ch1.§ 0.”7

Phaeophytin Q

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Fig. 6.1 Monthly variations of chl.g and total chl. at stations1 - 10

7AUTOTROPHIC INDEX

Introduction

Many studies have described the algal growth ofperiphytic communities in lentic and lotic waters. The majorityof periphyton studies have used artificial substrata (Cooke,1956; Sladeckova, 1962; Dillard,1969; Dumont, 1969; Hynes, 1970;Patrick, 1973; Rosemarin and Gelin, 1978; Cattaneo and Kalff,1979; Loeb, 1981). Periphytic growth on substrata and communitystructure are affected by a variety of factors such as hydrology,nutrients, grazing, period of exposure, temperature, depth andwater currents. The conditions reported for the optimumperiphytic growth by different investigators vary. This is dueto various limiting factors of the ecosystem. However, thegeneral trend in periphytic growth with regard to these factorshave been established. Periphyton communities are sensitive tochanges in water quality (wuhrmann and Eichenberger, 1975) andresponded to pollution by altering their structure (Patrick,1973). Studies on periphytic algal community structure have beenfound to be useful for biomonitoring of water quality (Cooperand Wilhm, 1975; Bott _t §l;, 1978; Rai gt §_;, 1981; Gaur andKumar, 1985). Singh and Gaur (1989) demonstrated the usefulnessof periphytic algal criterion for monitoring oil pollution inrunning waters. Periphyton communities have recently been em­ployed as biological indicators of acidification of lakes (Ste­venson gt _l., 1985). The utility of autotrophic index (AI) ofperiphyton in the assessment of water quality has been discussedin APHA (1992). No such studies have been done on periphyton in

_56_

Cochin estuary. The only information available is regarding thedistribution and factors influencing its colonization in theestuary (Sreekumar and Joseph, 1995a, 1995b, 1996). Hence thepresent study explores the utility of periphyton community inthe water quality determination of Cochin estuary.

Material and methods

Ash-free Dry Weight (AFDW)

Periphyton samples on glass slides submerged atdifferent stations were collected fortnightly over a period ofone year. Dry and ash—free dry weight analysis (APHA, 1992) wasdone using the slides expressly designated for the purpose. Thefortnightly values of ash—free dry weight were pooled forcalculating the monthly mean values.

a. Procedure:

The sample air-dried in the field and protected fromabrasion, moisture and dust were re-wet with distilled water.Glass slides were scraped with a razor and washed with distilledwater in to separate prewashed, tared crucible to collect all

materials that had accumulated on each substratum during Shecolonization. The material is air dried and then dried at 105 C,allowed to cool for 12 h in a dessicator and weighed to thenearest 0.1 mg. The samples were then ashed in a muffle furnace

O

at 500 C for 1 h, cooled to room temperature, wetted with dis­0

tilled water and dried again to constant weight at 105 C (tocorrect for dehydration of clays).

-57­

b. Calculations :

Ash—free dry weight calculated as the weight of the ashsubtracted from the dry weight, provided an estimate of the totalbiomass (autotrophic, heterotrophic and detrital) of theperiphyton community. The mean weight from each slide wasreported as dry weight and ash-free weight per square meter ofexposed surface. if 25 by 75 mm slides are used, then

g/slide (average)2g/m = ------------------ -­

0.00375

Autotrophic Index (AI)

The Autotrophic Index (AI) is a means of determiningthe trophic nature of the periphyton community. It is calculatedas follows :

Biomass (ash—free weight of organic matter), mg/m

(APHA, 1992)

Results and Discussion

The monthly mean values of dry weight mass (Dw) andash-free dry weight mass (AFDW) of periphyton at 10 differentstations in Cochin estuary for one year are given in the Tables7.1. and 7.2. The DW values varied from 2.66 to 47.01 g/m2. Theannual mean values of ow at Vaikom, Murinjapuzha, Panavally,Vaduthala, Kumbalam, Bolghatty, Chittor, Eloor, Njarackal and

-53­

Karuthedom were 24.56, 15.88, 16.71, 10.66, 9.92, 8.81, 15.07,13.60, 14.75, and 13.51 g/m2 respectively. Monthly average AFDW

for the estuary varied from 4.56 to 11.84 g/m2 with monsoonipost-monsoon and pre—monsoon recording 7.84, 6.70 and 8.21 g/m2respectively. The annual mean value of AFDW was 7.58 1 1.94 g/mfor the estuary. The highest single value of 19.00 g/m2 wasreported from Vaduthala in September while the lowest 1.21 g/mzfrom Eloor during July.

Spatial and temporal variations in AFDW in the estuarywere analysed using a 2 - way ANOVA (Table 7.3). A significantvariation occurred in the values of AFDW between differentstations (ANOVA; P < 0.05). A significant difference in AFDWwas also noted during different months in all the stations of theestuary (ANOVA; P < 0.05). Correlation of AFDW with chl. Qrevealed that there was significant correlation between AFDW andchl. Q (P < 0.05). The relationship between AFDW and chl. g ofperiphytic matter was very similar to that found by Liaw and MacCrimmon (1978) and Eloranta (1982).

Regression analysis of AFDW (X; mg/m2) and chl.; (Y;mg /m2) showed (Table 7.4) that up to 96% of the variation inchl.; can be explained on the basis of variation in AFDW. Highlysignificant correlation between chl.§ and AFDW is shown in scat­ter plots (Fig.7 .1—5).

The average organic content (%) of periphyton in theestuary was 55.60 t 4.48. The percentage varied from 33.29 to

-59­

74.12 (Table 7.5) at 10 different stations. Monsoon seasonrecorded the lowest percentage (48.49) of organic content. Therewas an increase of organic content during post—monsoon (57.48%)and the trend continued during pre-monsoon period (60.85%).Reduction in organic content of periphytic matter during themonsoon season (Table 7.6) in the estuary may be due to theturbidity resulting from freshwater inflow into the backwatersthrough various rivers. The lower percentage of periphyticorganic matter recorded at Murinjapuzha and Eloor which arelocated near the confluence of Muvattupuzha and Periyar riversrespectively into the estuary confirms this. with the decline ofmonsoon, turbulence in the water body also decreases. The in­crease in organic content of periphytic matter during the post­monsoon is in agreement with the above concept.

Monthly mean values of chl.g at different stations areshown in Table 6.1. The values ranged between 10.26 and 214.20 mgm2. The annual mean concentration of chl.g of periphytic algaewas 50.80 1 12.94 in the estuary. The average chl. Q values in

the zestuary during different months vary from 33.16 to 86.62mg/m

Spatial and temporal values of autotrophic index (AI)worked out for the estuary are shown in the Table 7.7. Highestsingle value of 280 was recorded at Kumbalam during March and the

lowest 66 from Panavally during May. As per the APHA (1992),normal AI values range from 50 to 200. The annual mean of AI ofthe estuary during the period of study was 154 1 20 and lie well

-50­

within the normal Al range. However, the annual mean values of 4stations approach near the upper limit of normal AI range.Vaikom, Murinjapuzha, Bolghatty and Karuthedom recorded annualmean values of 194, 194, 179 and 163 respectively. Incidentlythese stations have recorded negative values of net dailymetabolism (NDM) during different seasons in earlier studies.Vaikom and Bolghatty stations are known for their proximity tothe collective efflux of domestic sewage from the adjacent towns.Non—viable organic materials in these stations also must havecontributed to the higher AI values. Earlier studies (Crosseyand La Point, 1988) had shown that Al could be a better indicatorin the case where a pollutant such as sewage detritus caused ashift from an autotrophic to heterotrophic community. Moreover,isolated high AI values were noted even in stations where theannual mean was < 150. This clearly shows that the trophicstatus of the estuary is highly vulnerable. Significant varia­tion in spatial and temporal AI values (2 way ANOVA; P < 0.05)also confirm this. Summary of ANOVA of AI values are shown inTable 7.8. Fairchild gt g_L (1989) had reported AI valuesranging from 6614 to 242 t 28 in Lake Lacawac, Pennsylvania.

Artificial substrate were retrieved from study sitesafter the optimum period of exposure. AI value is directlyaffected by changes in AFDW and chl. Q; The AFDW values in turnare influenced by the nonliving organic matter (detrital) thatmay gather on the substrate. Nonetheless, continuous monitoringof different locations in a large water body such as Cochin

-51­

backwaters with a standardized procedure for AFDW and chl. Qdetermination can yield reliable data regarding the trophicstatus and water quality.

Summary

Using artificial substrata (25/75 mm glass slides) ow,AFDW and chl.g of periphyton were determined. There wassifnificant correlation between AFDW and ch1.g. These parameterswere employed for the calculation of Al.

The annual mean AI value for the estuary was found tobe 154 1 20 which is within the range of AI values for normalwater conditions (APHA, 1992). Vaikom and Murinjapuzha stationsrecorded higher annual mean AI values near the upper limit of thenormal range.

All the stations studied recorded occasional very highAI values, indicating low water quality. The study shows theutility of AI as a criterion for assessing water quality in thebackwater.

-52­

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m.uoow m.nan u.n¢on ¢.N.h¢H n.unm¢H.~G0mH u.nmmofi o.meno m.nwon m.nmsnH.maam ¢.mno¢ o.<maH H.¢hHmH n.omonn.ammm n.¢nnufi ¢.8mHhH o.ssmm u.mmnmn.mmmm u.maan H.nmmm a.¢unm ¢.cnomm.nnu¢ m.mm¢m H.momn m.nm¢m ¢.mmm¢m.nqmm m.fi9am h.HH¢¢ m.omma m.ma¢m

n.w¢m¢ H.8Hmh ¢.smmo a.o¢sm ¢.mmmafim.muom n.mnmm m.omo¢fi o.mmmo a.fiamflHn.nm¢m m.¢¢¢nH m.¢mamH m.sm¢nH m.nmunH

>mZ .La¢ .LmZ .nmu .cmn

........... -HWHm.M.H_---------­

H.SHaaH

o.snmu¢.HO0MH.smom¢.&00Hfl.&D¢flH.&9hHH.¢hhm

m.mwmmHn.mmmmfi

¢.smmmHW.¢w¢hH

¢.Hflahm.finom¢.umHmh.HflHHu.m¢mmo.ummn

.HH¢£m.onmmm.mmamm.nmmmW.Qh0H

¢.HDQHH

m.cmmo

0.flS0¢Hm.flNSGH

n.mnooH.¢nmm

N.DGG&Hfl.H&&hH

o.mm¢n

m.¢hNOH

.U¢Hfl

m.¢¢nH .0m.amnn .m~.hHHm .hH.00H¢ .0

>Lm:umm cwcuou ca mcofiumum ucmLm+

m.Hh@N m.mHHHH.¢Gah N.HmHhm.mmmo H.hNHm

h.&®flfl «.Hh0HH.GflflNH ¢.maom

m.HmHH« H.mmHSH

0.WHUGH H.0H¢H

w.fl¢hHH n.mmmmH

.a:¢ .H3m

cDUmc0E

wwu um c0v>caHLmQ +0 3Qu¢ +0 mm:~m> cmwe >~£uco£

H.h mflnmk

Table 7.3 ANOVA of AFDH of periphyton in Cochin estuary

Source SS DF MS F6667661; """ 366261662766 """" '11 """ '36363666T66""2T32E"Bet. Rows 742131008.00 9 82459000.00 5.539Error 1473909632.00 99 14887976.00Total 2596242432.00 119

2Table 7.4 Linear correlation between AFDH (x; mg/n ) and

2ch1.g content (y;mg/m ) at different stations

in Cochin estuary.

Stn. Regression equation n rNo.

1. = 2.7899 x + 34.1961 12 0.5746= 3.7466 x + 10.3449 12 0.8548= 0.010 x + 0.7882 12 0.9616= 3.0779 x + 19.5035 12 0.8690= 5.7393 x + 12.7183 12 0.7553

Y

Y

Y

Y

Y

. y = 0.0071 x — 4.7926 12 0.8992y = 2.7142 x + 75.7230 12 0.5450y = 7.1350 x + 5.2916 12 0.9433y = 2.9116 x + 19.9488 12 0.8929Y = 4.7295 x + 12.6007 12 0.7793

30 +0 -\. Cw mW5.__M>H0.m¢ ¢u.¢m ms.mm n¢.oo ¢H.N0 ¢¢.80 HH.MD mfi. M Nh.0¢ Hm.N¢ mm.om &¢.hD .0mn.m¢ m¢.¢m nu.an m¢.om nm.nm um.nm mu.¢¢ ¢n.mm nu.o¢ DH.NH ¢n.m¢ Nm.HD .m¢a.mm HD.H0 m¢.nm SD.0¢ mo.om ou.«m ¢u.mo nm.oo ¢H.ND mo.¢m ¢m.o¢ HH.G¢ .hnm.¢m ¢0.Nh om.sn am.oo ¢m.mo m¢.m¢ &H.Nm mm. m fim.mn ¢m.Hn mo.¢n em.o¢ .0um.oo Hm.sn fim.mo 0N.N0 nm.mm ¢h.0¢ nn.wm ¢m.m¢ mm. H m¢.um on.o¢ no.¢m .Dam.¢m en.mo ¢m.mm mm Dd 06.4w mnsuo a¢.um nm.nm D¢.H0 ¢o.mm om.mm mu.mm .¢ma.¢m em.un Gh.¢D mm.oo no.sm NN.Nh mm.¢o ®¢.m0 ¢huUD mu.nm m¢.Hn nm.mm Hha.H un.¢o mm.mo ¢n.nm NH. W H&.¢n un.n¢ HH.G¢ nm.mn ¢£.H¢ hM.N¢ H¢.m¢ .N

mu.on ¢D;Sh D¢.DH 8H.¢0 mH.mm N«.¢h mo.uo 0H.H 0H.H¢ om.om mH.nm mu.u .H

.1 nu uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 4%.>mE .La¢ .Lmz .nmu .:mn .UmQ .>0Z .uuO .#umm .m:¢ .Hjn .c:n .cum

......... -.mHmH.o.HHm_---------- ----------mmUHwm------------ ------------mm.m_a-----------­

m.n m_nm»

>Lm:umm cficuou cu mcomumum ucmLm++flu um :0u>£Q«Lma +0 ucmucou UHCMOLD +0 mm:mm> cmme >H£HCUE

Table 7.6 Sesonal averages of organic content of periphyton atdifferent stations in Cochin estuary.

Stn. Monsoon Post—monsoon Pre—monsoonNo

I """"" "2935 """""""" "3236 """"""" "8575 """ "2. 42 67 49.48 56.183. 49 71 71.44 70 264. 54.80 56.45 57.155. 47.82 52.95 65.556. 48.02 55.11 65.967. 49.18 57.82 56.888. 45 16 47.62 53 259. 50 75 57.79 54 6610 49 00 61 94 59 57Values in % of Dw

mmfi .mH NEH am. mm" mfi Hm“ mwm BAN um“ um“ ¢NH .GH

mom awn om“ ¢BN mm_ mm“ mmm smfi mug NHH “NH SHH .0wm flea nu flaw «ea 08“ mmfi Bmfi mag nu“ no No .m#8“ S¢N DHN sfifi «Ha m¢u cmfi MM“ mm“ Sufi sag mafi .hsfiu ¢HN sen can GHN emu fim” mmfi mmfi «ma ONH SHH .0¢H« flag emu msfi Nfia nag Rafi med hfifi Nafi msfi SNH .m

mfifi WENT flu“ ¢Gfi Mfia ma” NHH flea s¢m mom osfi NEH .¢no MSH Sufi sm mm mm am N0 ¢m hsfi NHH cm .H

mofl cmm sum sum mam GDN Hnfl mo“ mmfi BGH Sfifi SHH .N

¢mfi emu fimfi s¢m saw smfi mug sea mhfi ¢flfi Sm” aha .H

>mE .L&¢ .LmE .nmu .Cmw .UmD .>UZ .uuU .pumm .m:¢ .~3n .:jn .cum

....... -m..wmHM_M----- ----,._m.m,..m.Hmm_----- -------m.m.,_w_-------­

>Lm:umm cflnuou cg mcoflumum ucmLm++«U wm :nu>£Q«Lmn +0 H¢ +0 mmJHm> cmme >~£vc0Z h.h mmnmk

Table 7.8 ANOVA of A1 of periphyton in Cochin estuary

Source SS DF MS FB;?'EZ.1; """"" EIIBBTEB """" '11 """" ‘£93332 "" ‘E7332’Bet. Rows 117135.66 9 13015.07 6.414Error 200872.53 99 2029.02Total 370109.00 119

#

Stn.1

+

+* ++++++-O-++++++++++++++++"****T* ‘- ufdw55.11 135408486

ch l oroph67.66

I'­

+­

++

4»

0

4­

5­

0

.\.

4­

4­

++

4­

++6­

A­

0­

4­

4­

4­

4­

J+4­

5

bvb

#­

+ o-4-+0-++++++++++++++-0-+4-44.¢'+4AL++++¢-­|0.'l(}

|~|3|§nsh

I IE-‘NJ

Fig. 7 .1 Linear correlation between AFDW (xung/m2)and ch1.g content (y: mg/m2) at stns. 1 E 2

eh! a214.2

1|’­

Stn.3

. + + + + + +

+ + +-r+ + + + +4-+ + +-++ + + + + .

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +35.?) Hf Uh’2340 [7992Chl a79.19

++

++++-0­

++++++-I­

+++

++

+++ ++++ 1'»+++++++++++++++-i-+4 + + + + + + 4- + 4- -0- + -0­lG.5B AFDW1670 IHOOSFig. 7.2 Linear correlation between AFDW (x: mg/m2)

and cl1l.g content (y;1ng/1:12) at stns. 3 8 4

Ch]68.76 Stn.5 ‘+

++

++4­

+-0­

++++++-0­

++++++++++ II+ -4-++++++++++-O-++++ -l- + + + + + + + + + + + +l8.27 AFDW1973 8182

Chl'71 G5

Stn,6

++++-4-+4-++-I-+++-O-++++++4-++++++++10.8-"I AFDW2055 9872Fig. 7.3 Linear correlation between AFDW [x:mg/m2)

and ch1.g content (y:mg/H12) at stns. 5 8 6

Chll3B.02

++++++4­

+-0­

++++++

+++4­

++++++++++++++++++++++++++++++++ + + + +12.66 AFDW.215 17454

Chln5.39

+-0­

+++++++++++-0­

++++4­

++++++

+

-0­

:1­

=0:+++++++++++++-4-+++++++++++++++2.1_45 AFDW3900 |7l50Fig.7.4 Linear correlation between AFDW (x;mg/m2)

and ch1.g content (y;mg/m2) at stns. 7 B 8

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +352‘:2047 ‘Chl215.5-1

Stn.10

+

++++4­

+4­

++++++++++++-0­

++++ II

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +14.07 AFDH2539 14722Fig. 7.5 Linear correlation between AFDW (x: mg/m2)

and chl._a_ content (y;mg/m2) at stns. 9 E‘: 10

8PRIMARY PRODUCTION

Introduction

The total primary organic production in an aquaticecosystem is very often used for the assessment of the fisheryresources.Estimation of primary production is generally done withphytoplankton community, though other autotrophic gorups such asperiphyton and macrophytes are present in varying quantities indifferent environments.In a shallow estuarine ecosystemperiphtytic and sediment dwelling algae also contributesignificantly to the total primary production in addition tophytoplankton. Several studies (Qasim et al., l969,1974;Nair etal., 1975; Qasim, 1973,1979;Gopinathan et al., 1984) were made on

the primary production in Cochin estuary. Qasim (1973) estimatedthe gross production in the estuary to be 0.35 to 1.5 gC/m2/day.In the Vembanad lake adjacent to Cochin estuary , Nairet al.(l975) have recorded an average production rate of 1.2 gC/m2/day.This may be an underestimation since the contribution tothe total production by autotrophic groups such as periphyticalgae, sediment microflora and macrophytes was not included whiledetermining the production values.The quantitative estimation ofproduction in any environment excluding periphytic and benthicalgal communities where they are present in significantproportion, is far from the real value.The aim of the study is toassess the role of periphytic algae in the primary productivityof Cochin estuary.

-53­

Material and Methods

Measurements of primary productivity were made usingGaarder and Gran's light and dark bottle method as described byStrickland and Parsons (1972) and APHA (1992).The dissolvedoxygen values for the initial,dark and light bottles weredetermined by winkler method. The difference in oxygenconcentration (ml/1) between light and dark bottles was convertedinto its carbon equivalent (mg C/l) for gross production and thedifference between the light and initial values was convertedinto carbon equivalents for net production.

(a) Sampling : BOD bottles, 300 ml, clear and opaque borosilicateglass with ground glass stopper were used for sampleincubation.The bottles were acid cleaned and rinsed thoroughlywith distilled water. As a precaution the entire bottle (dark)was wrapped in aluminium foil or placed in light proof containerduring incubation.Small glass slides of known surface area weresuspended 30 cm below water surface using a wooden float forsimulated colonisation (2 weeks) of periphyton (Sreekumar andJoseph, l995b).Periphyton community samples for productivityestimation were obtained by fortnightly collections from tendifferent locations in Cochin estuary.

(b) Procedure : At each station both the light and dark bottleswere filled with water collected from the region, the periphytonsamples were obtained.The bottles were thoroughly rinsed justbefore use, with water being tested.Productivity and respiration

-64­

were determined by inserting small glass slides with periphyticgrowth into the bottles. The samples were incubated for a minimumperiod of 2 h. A set of Gaarder-Gran light and dark bottleproductivity and respiration measurements were also made toobtain a correction for phytoplankton metabolism.

(c) Calculations : The gross and net primary production andrespiration of periphyton community were calculated (APHA, 1992)as follows :­

LB LB IB DE DE IBP : - - — — — — — — — — — — — — — — — — — — — — — — - - — — — — -­

Gt x A

where :

2P = gross production, ml 0 / m /h,G 2V = Volume of light bottle ,1,

LB

C = concentration of 0 in the light bottle,LB 2ml/1, corrected for phytoplankton metabolism,

C = concentration of O in the initial bottle, ml/1,IB 2V = volume of dark bottle , 1,

DB

C = concentration of O in the dark bottle, ml/1,DB 2corrected for phytoplankton metabolism,

rt ll length of exposure, h, and2

substrate area, mIn n

-55­

Periphyton community respiration was calculated by :

R = ——————————————————————————— -­t x A

2R = community respiration, ml 0 /m /h,

2

V = volume of dark bottle , 1,DB

C = concentration of O in the initial bottle, ml/1,IB 2C II concentration of 0 in the dark bottle, ml/1,correctedDB 2

for phytoplankton metabolism,

t =length of exposure,h, and2

A = substrate area , m

The net periphyton community production (P ) was determined asN

the difference :P : P — RN G

Assimilation Number (AN): It is the amount of carbon assimilated

divided by the amount of chl.a (mg C/mg ch1.a/h).This ratio is anindex of photosynthetic carbon production per unit chlorophyll(Raymont, l980).Larger AN values indicate relatively moreproductive photosynthetic assemblages.

Production/Respiration Ratio (P/R): Calculated by dividingcommunity production (GPP) by community respiration (CR ).This

24ratio has been used to classify aquatic systems as autotrophic

-55­

(P/R > 1 ) or heterotrophic (P/R<1) (Odum ,1957, Vannote et al.,1980).

Net Daily Metabolism (NDM): It is calculated deducting dailycommunity respiration (CR )from daily gross primaryproduction.This parameter E: equivalent to woodwell andwhittaker's (1968) net ecosystem productivity, Odum's (1971) netcommunity productivity and Markers (1976) net photosynthesis.NDMis positive during periods when photosynthesis is greater thanrespiration (ie., autotrophy predominates) and the system isaccumulating organic matter.NDM is negative when the converseoccurs and heterotrophy predominates with the net organic matterdegradation.

Results and Discussion

Gross Primary Production

The monthly mean values of gross primary production atdifferent stations in Cochin estuary are shown in the Table

28.l.The highest value of 296.66 mg C / m /h was observed at

2

Panavally station in September whereas the lowest 29.75 mg C/m /hwas reported from Eloor during July.The average production forthe estuary during different months was in the range 87.86 to181.56 mg/C/m2/h.The monsoon ,post- monsoon and pre-monsoon mean

values of periphyton production were 131.36,109.03 and 118.78 mgC /m2/h respective1y.The rate of production was found to be thehighest during monsoon and lowest during post monsoon.The annualmean periphyton production calculated for the ecosystem was119.77 mg C/m2/h.

-67­

2Marker (1976) had reported 83.62 mg C /m /h periphyton

primary production in southern England streams.Very litte data isavailable for comparison of production values of this ecosystemwith that of other estuaries .wiley et al. (1987) found thatprimary production in a prairie river system from below detectionlevel to about 50g 0 /m2/d.La Perriere et al. (1989) had reported2 2 290.63 mg C /m /h and 87.5 mg C/m /h of gross primary productionin high subarctic streams such as Chatanika river and DeltaClearwater Creek respectively.

The variation observed in regard to gross primaryproduction both spatial and temporal were analysed (Table 8.2)using ANOVA.A significant variation in gross primary productionoccurred between different stations (ANOVA; P<0.05).Similarlythere was a significant variation in primary production duringdifferent months of the year( ANOVA ;P<0.05).The incidence ofthree well marked seasons on account of the south west monsoon

must be responsible for the temporal variation in primaryproduction.The stations studied were located at places where someof the major rivers join the estuary or near big industrialconcerns that discharge effluents into the ecosystems or nearbarmouth where comparatively higher salinity was observed.Thechanges in hydrographic parameters due to tidal waves also musthave contributed to the variations in primary productionspatially.

Correlation of periphyton production with biomass(chl.§), standing crop (cell count), hydrographic parameters such

-53­

as salinity , temperature, dissolved oxygen, pH and nutrientssuch as nitrites, phosphates and silicates was studied by workingout the correlation coefficient, r value (Table 8.3).There was noconsistent correlation between primary production values andhydrographic parameters studied.However, production values showedsignificant positive correlation (r= 0.7112,P<0.01) withtemperature at Njarackal and with NO —N (r= 0.6032, P<0.05) atE1oor.Corre1ation studies of peripiyton biomass (chl.a) andhydrographic parameters made earlier also yielded similarresults.There was significant positive correlation betweenstanding crop (cell count) and production in most of the stationsstudied.Lack of correlation observed in some stations may be dueto the characteristic floral composition of the site.In almostall the stations studied there was significant correlationbetween gross primary production values and chl.a(P<0.0l).Significant correlations are shown in scatter plots(Figs.8.1- 8.3).

Assimilation Number

The monthly mean values of assimilation ratio for theperiphyton are given in Table 8.4.The highest value of 7.29 wasobserved in July at Murinjapuzha and the lowest 1.1 in January atPanavally.The monthly mean values of AN for the entire estuaryvaried from 2.21 to 3.05.The monsoon , post—monsoon and pre­monsoon values were 2.48,2.49 and 2.54 respective1y.Curl andSmall (1965) suggest that several factors may affect theassimilation number that it cannot be regarded as a constant.The

-59­

assimilation number in the estuary, remains more or less the sameduring the monsoon and post monsoon.A slight increase in thevalue was noted during pre—monsoon period.This may be due to theextended period of sunshine and sufficient light penetration onaccount of less turbulence in water.Joint and Pomroy (1981) hadsuggested a higher rate of primary production when water is lessturbid.The conditions are just the reverse during monsoon andpost monsoon .The average value of assimilation number calculatedfor the periphyton of the estuary is 2.5 which is well within therange (2-6) suggested by Strickland (1965).There is no evidencefor the influence of nutrient concentration on periphytonassimilation number in this estuary.Strick1and's view thatnutrient deficiency reduces the values of assimilation number isnot supported by Steele and Baird (l96l).The difference _inassimlation number at different stations were analysed ( Table8.5) using ANOVA.There was no significant variation neitherspatial nor temporal with regard to the assimilation ratio ofperiphytic algae in the estuary (ANOVA; P < 0.05).

Community Respiration

Monthly mean values of periphyton communityrespiration (Table 8.6) at different stations varied from 10.80to 120.22 mg C/m2/h.The highest monthly average value of 81.62mg C / m2/h for the entire estuary was observed in September

2while the lowest rate of 39.30 mg C /m /h was noted inOctober.The monsoon, post-monsoon and pre—monsoon values of

2

community respiration rates were 57.71 ,55.05 and 58.22 mg C/m /h-70­

respective1y.Pre—monsoon recorded comparatively higherrespiratory rates possibly due to the increased temperatureconditions.The annual mean value of the respiratory rate for the

2estuary was 55.05 mg C/m /h.

Net Daily Metabolism (NDM)

Temporal variations in NDM at different stations aresummarised in Table 8.7.During monsoon all the stations exceptMurinjapuzha (stn.2) Vaduthala (stn. 4) and Karuthedom (stn. 10 )were dominated by photosynthetic assimi1ation.In Septemberrespiration was predominant at Murinjapuzha and Karuthedomwhereas at Vaduthala respiratory activity dominated in August andSeptember.In the post— monsoon, autotrophy again predominated atmost of the stations.However, four stations viz. Vaikom ,Murinjapuzha , Bolghatty and Chittoor showed dominance ofrespiration during December. During pre—monsoon, heterotrophy(observed as dominance in respiratory activity ) dominated inmost of the stations except at Panavally and E1oor.Butphotosynthesis was dominant during April and May atKaruthedom.Panava11y and Eloor are two stations where autotrophy

predominated throughout the year.A1most the same conditions wereprevalent at Kumbalam except for March when respiration wasdominant.Deviation of NDM from zero on either way can beexplained by the dominance of autotrophy or heterotrophy.Resultsobtained during the study are explained on this basis.NegativeNDM values at Vaikom and Bolghatty during post—monsoon and pre­

monsoon resulted from the predominance of heterotrophic_71_

components of the periphyton community.These stations by theirproximity to sewage discharges are highly polluted due todecomposing organic matters.The environment in these stationsfacilitates the dominance of heterotrophic component of theperiphyton community.During monsoon , heavy freshwater flushingat these stations remove degrading organic matter and NDM will beon the positive side.Eloor station located near the discharge oftoxic industrial effluent from FACT and Cominco Binani Ltd.showed positive NDM values throughout the year.This can bepossibly due to the harmful effect of toxic material on the moresensitive heterotrophic components.The fact that the environmentwas not conducive for autotrophs was evidenced from the lowincidence of periphyton standing crop as well as chl.§.Hornbergergt El; (1977) devised a scheme for evaluating water quality onthe basis of production and respiration since NDM is affected bya variety of factors influencing autotrophs and heterotrophs, itsutility for the evaluation of water quality in the highlyfluctuating estuarine environment is doubtful.However, continuousmonitoring of specific locations with regard to metabolicactivity wil reveal the trophic level changes taking place andits relation to the changing environment.

Production/ Respiration (P/R)

Monthly mean production / respiration ratio (Table8.8) at different stations can also be conveniently used fordetermining the trophic level existing at different locations andperiods.P/R value is > 1 when NDM is positive and is < 1 when NDM

_72_

is negative. NDM value of zero is functionally equivalent to aGPP: R value of unity except that NDM is an absolute value

whereas2éPP : R24 is a relative assessment of system metabolism.

According to Nair gt gl; (1975) planktonic productionis 1.2 g C/m2/d and the total production estimated for theestuary and the adjacent backwaters is about 100,000 tonnes ofcarbon per year.Periphyton production observed during the presentstudy is at the rate of 1.4 g C/m2/d.The estuarine complex having180 km boundary with an average 1 m depth can assimilate about92000 tonnes of carbon per year.Periphyton production in theestuary is thus upto 92% of the planktonic production.Thephytoplankton and the periphyton together contribute aboutl,92,000 tonnes of carbon per year towards total primaryproduction in the estuary.

Summary

The primary production of periphytic algae in Cochinestuary was investigated.Periphyton colonised on artificialsubstrata were incubated in light and dark bottles.Production wasestimated by measuring the changes in dissolved oxygen.

Periphyton production did not show significantcorrelation with the hydrographic parameters studied.Howeverthere was significant positive correlation between gross primaryproduction and biomass (Chl.g).

-73­

Significant variation (spatial and temporal) exists inthe rate of primary production at different stations of theestuary.

The annual mean gross primry production of periphytonin the estuary was estimated as 119.77 mg C/m /h.Monsoon seasonwas comparatively more productive than post-monsoon and pre­monsoon.The phytoplankton and periphyton together contributeabout 1,92,000 tonnes of carbon per year towards total primaryproduction in the estuary.

-74­

mn.nfim hh.HmHH sm.mmH

¢u.¢m

¢W.&§H SH.¢NH

mn.nm|.uII-|...\Pf Cron.soon.onna.mooo.s¢

mm.Hm

mfi.¢NH

¢m.mn

H mn.o¢fi&fl.hGHH mm.¢mH

so.mo no.ooH

mn.mmH «o.nn

ma.mn sa.s¢fin¢.moH Nfi.haH

_s.mm mo.n¢on.m¢ m¢.¢n

o¢.mo ¢N.h£Hmw.mnm mm.noHHm. ma no.mmHnm.¢nH nn.mcfi

.Lm: .nmm

ElmLm

Ac0u>£nmLmQ. COnHU5UDLQ >LMEH

Hh.NSumm.ooHaN.hhH

H.Ho0¢.¢hmo.«o

&O.NNHHN.h¢H

88.¢SHnm.oomhH.D8Nmn.no~¢H.88aom.nnmnn.oom

o~.H&

0H.8DHmS.GNflDm.HHHH.mNHNH.hSNHG.hHa

mn.mm

o¢.mmHmm.nafl

sa.nmOH.~h

ms.emm

&h.¢h

¢h.fl®H

am.muH

flH.0mmm.Ho

Dn.mHH

¢a.mm

flH.nHHha.HNHhH.hGHNH.amH

.:\ exuxme.

:1P

os.omu nn.om

nm.um ¢n.mfifimm.mb HH.NDN

o¢.mo h8.mHH

&H.mN mo.¢m

0h.m8H 0N.h8H

M0.«N nm.on

NH.8flH 0N.m8H

sm.mo «m.mm

m¢.G&H WH.ShH

.umQ .>0Z

CO0mCDE|#mUl

.m:D«um#m HCMLW++wU um

Ln mmoLm +0 mm:Hm> cmme >~:u:0E

H.m mgnmk

Table 8.2 Analysis of variance (ANOVA) for the periphyton primary production

Source of Sum of Squares Degrees of Freedom Mean Square F ratiovariation

5.256

12346.1?

1111115.75

Bet. Cole

2.182

5138.29

11

56433.15

Bet. Rows

2351.63

9?

232311.34

Error Total

119

460360.24

omms.su

HN&A.Gnmm«.eHShD.QSOHH.Somcm.s

om¢e.s:mmmm.a:

¢nmu.s

Hm " _.:U_UmWL+ WU

mmmLmmD

AHG8.8 v 1. Hm>mH NH um ucmuM+ficmfim lI.**.

Ama.s.a v av Hm>mH NW um ucmufl+ficofim ll

.9 25.9:

momm.s: ofiom.sn h&NM.8 hHhS.8I N~Hh.8** mmmm.s nm¢m.sNH80.8* fi¢sm.a anHe.a: am¢m.a ~mHH.G H0oQ.8l manm.ssmmm.sn mmH¢.s hSM8.8 mmHs.s mm¢u.an m¢¢fi.su fl0flH.8mmmo.sn mmn¢.au NH¢0.8l m¢mm.s: ¢Hm¢.OI ooom.su 00NH.8

¢¢mm.s ¢HSH.8 nmmu.sn NOHMJSI hHh8.GI mHoH.8I ¢0Sm.S#*

msmu.a MN¢fiAS m¢¢fi.s: hHNH.B Nh¢8.Ql N¢HH.Q momu.snNo0H.8I sH0~.8 oo¢s.s SmSH.8l ¢D0S.8I ¢H¢H.sI «hau.8lomm¢.su 8HHM.8 hHNH.G omafi.a| mons.a N¢0H.G omoo.s*

m&hH.8 m&hH.8 mmnm.s\ ¢SN8.8 mnno.a: mHam.su nmHs.s

....................................................................... mam­

N H

2: oz oflm za on dew» 33.2mm mcflucmum

mLmumEmLma AmucmEcoL«>cm Ucm QDLU mcwucmumgm .H£U

m.m mfinmk

ncm cowuu:uoLa cou>LufiLmu cmmzumn Am:Hm> L. ucm«u«++m0u CUw#mHwLLDU

¢mmo.o**8¢fl&.Q**mmmo.a*mneno.e**moom.e**Hflhm.S**Hmmo.a**

_hmn.a¢

ommo.a**momo.a**

Table 8.4 Monthly variation in assimilation ratio of periphytbc algae

at different stations in Cochin estuary

Mofisoon

Pre-monsoon

Post-monsoon

May

Apr.

Mar.

Feb.

Jan.

Dec.

Nov.

Oct.

Sept.

Aug .

Jul.

Stn. Jun.

TE‘

2-OJ

2.46

2.40

2.24

2.45

'7 '7’4.. 4.‘)

2.31

2.27

a-, .1-.1.. 4...‘

2.11

4.28

H '3"1.. st.‘

.54

(*4ID

1.97

5.21

.78

1.68

2.02

7.29

N

2.18

.14(‘4

4.37

1.10

2.16

3.04

2.76

1.38"

1.82

2.51

2.94

.16I’:

2.78

3.04

3.12

.64

N

2.89

3.25

2.60

3.01

4

1.92

2.54

1.70

1.84

1.97

1.56

1-!

2.18

"J '3"4. - Ln.‘

U7

Cl

2.74

.61N

2.71

ll‘!

N

2.48

2.65

2.41

ln

N

2.76

2.48

2.60

ID

('4

U1

(‘4

2.24

3.02

2.49

2.80

2.39

U")

N

2.60

2.54

2.82

2.61

2.73

2.02

2.12

2.68

2.35

1.95

1.93

2.04

'.'’E

4.. s.‘.J

2.47

2.72

2.38

1.98

("-1

N

2.54

2.21

U")

N

.02N

1.96

2.43

2.61

2.81

50

1.68

2.54

1.78

2.76

2.30

1.89

'7 '73:‘4.4 4.4

2.19

NN

10 2.60

Rafi fiU.$m Hmuop

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on.ao

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om.om

sm.no

m8.aNH

om.nm

mm.¢mfi¢¢ummN

sm.Ho

uN.Hc m<.¢m

wm.mm: om.mofi:

um.m¢ ¢m.¢m:

un.omH on.m¢fi:

ua.m¢u n«.mHNun.snu so.¢nmu0.&NI on.mn:uN.mhI mm.m¢H

.La¢ .LmE

c00mc0EImLm

+0 AZQZV emfifionmume >~«mD um: +

mm.nnu on.sofi¢o.mun mn.H¢fi

om.o mm.nn

mm.¢ on.u

oH.on: oa.¢¢u

aH.umH m¢.onmH.nn mm.nfi

¢m.mn on.¢muG¢.&¢HI so.onH

¢8.HHHI om.smHn

.nmu .cmn

Aux exu me.

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0 mm:Hm> cmme >H£u:o£

Dwumym HCNLW++wU am >#mCJEEDU cDu>£QmLmu

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a3+++++++++++1>+++++§++#++4++

9CONCLUSIONS

The photosynthetic component of periphyton,themicroorganisms growing on submerged surfaces in water , includesa diverse assemblage of algal forms that contribute significantlyto the total primary production of various aquaticecosystems.Earlier investigations on these flora, which escapedour attention so far,revea1 that they are very sensitive towater quality and hence serve as reliable indicators ofpollution.The autotrophic index of periphyton is generallyconsidered as a useful criterion for the assessment of waterquality.Changes in the floral composition and community structureof periphyton are quite often interpreted in relation to theaquatic environment by several investigators. No such studieshave been made from Cochin estuary. The ecophysiology ofperiphytic flora of Cochin estuary has been investigated in viewof its importance in the above aspects.

Due to the lack of retrievable natural substrata atthe desired sampling site, the suitability of differentartificial substrata such as clay tile, wood, glass, metal,painted surface, bivalve shell, plastic and rock and the durationof their exposure for optimum periphytic accrual have beenstudied. For the first two weeks, the rate of colonisation wasfound to be exponential on all the substrata. Periphytonconcentration varied with the texture of the substrata and thosesuch as wood, glass and bivalve shells showing comparativelyhigher concentration of periphytic a1gae.However no preferential

-75­

accrual was observed among the various species. The algaerecorded from the different substrata were mainly of pennatediatoms.0f the hydrographic parameters studied, salinity wasfound to have profound influence on the periphyton standing crop.

Periphytic algae of Cochin backwater comprised of 40genera and 76 species. Among these 31 genera belonged toBacillariophyceae,seven genera to Chlorophyceae and 2 toCyanophyceae.Out of the 31 genera of diatoms, 24 were pennalesand 7 centrales.Irrespective of the conspicuous seasonalvariations, 30 species such as Amphora angusta, Gyrosigmaspencerii, Navicula gracilis, Nitzschia obtusa, Pleurosigmaaesturaii, and Thalassiosira subtilis were found distributedthroughout the year, exhibiting wide tolerance of salinity. About15 species such as Gomphonema sphaerophorum, Nitzschialonqissima, Closterium acerosum, Cosmarium contractum, Q;pyramidatum, Spirogyra jggensis and Stiqeoclonium flagelliferum

were reported only during monsoon period.These are freshwaterforms.Certain species such as Achnanthes coarctata, Coscinodiscusradiatus , Gyrosigma macrum, Hantszchia amphioxys and Triceratium

reticulatum were reported only during premonsoon when thesalinity of the estuary is higher.Thus periphytic flora is foundto be composite in nature due to the fluctuating hydrography andrecruitment of the flora from the sea and rivers into theecosystem. The periphyton standing crop in the estuaryvaried from 9.8 x 103 to 1.6 x 104 cells /cmz. Though salinitywas one of the major factors influencing periphyton growth there

-75­

was a lack of consistency in the correlation of this factor withits standing crop.This may be due to the variation in the floralcomposition of periphyton at different parts of the estuary.Thediversity index <Shannon and Weaver> of periphyton was in generalslightly higher than that of planktonic algae in theecosystem.Similarity index of periphytic flora between majorityof stations was <60 indicating the extent of variation.Diatomsform the dominant group of the periphytic algal community as inother ecosystems.The common occurrence of species such as Amphoraangusta, Gyrosiqma spencerii, Navicula gracilis, Nitzschiaobtusa, Pleurosigma estuarii, Thalassiosira subtilis, Mougeotiaadnata and Oscillatoria sp. throughout the year indicates thatthey are the typical euryhaline forms of this estuary. Theannual mean value of chl. Q of periphyton in the estuary

has been estimated to be 50.84 mg/H3. This comparatively highmagnitude of chl.§ highlights the role of periphyton in theprimary productivity of the estuary.The temporal and spatialvariations in the distribution of chl.§ were significant {ANOVA;P<0.05}. The annual mean values of chl. b and chl.c of

periphyton were 6.36 and 12.57 mg/ml respectively.The ratio ofchl.§ : b being , <2:l and comparatively higher value of chl.cindicate the dominance of diatoms in the periphyton of thisecosystem as also evidenced by the floral composition.

The autotrophic index of periphyton at differentstations in the backwater varied from 66 to 280.The annual mean

value of Al was estimated to be 154 :20 which is well within the

-77­

range (50 -200} prescribed for normal water quality [APHA,l992}.However the annual mean values of AI at stns. 1,2,6 and 10 werenear to the upper limit of normal AI range. Isolated high AIvalues were also recorded even at stations where the annual mean

was <l50.The high values at different stations indicateoccasional degeneration of water quality.AI is a useful criterionfor monitoring the water quality of the estuary.

The periphyton productivity was estimated usingartificial substrata kept submerged at different stations forsimulated periphytic growth.Periphyton colonised on artificialsubstrata were incubated in light and dark bottles and productionwas estimated by measuring changes in the concentration ofdissolved oxygen. The annual mean production has been estimated

to be 1.4 g C/m2 /d. The estuarine complex having 180 kmboundary with an average lm depth of periphytic growth assimilateabout 92,000 tonnes of carbon per year which is almost of thesame magnitude as that of planktonic production {100,000 tonnesof carbon} from the estuary and the adjacent waters reported byNair et al.{l975}.Periphyton productivity in the backwater isthus estimated to be 92% of the planktonic production.Thephytoplankton and periphyton together contribute about 192,000tonnes of carbon per year towards total primary production.

-78­

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