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Distribution and Abundance of Horseshoe Crabs in Asajaya Mangrove Forest
Diana Bazila binti Shahruzzaman (30004)
Bachelor of Science with Honours
Aquatic Resource Science and Management Programme
2014
Distribution and Abundance of Horseshoe Crabs in Asajaya Mangrove Forest
Diana Bazila binti Shahruzzaman
The Final Year Project is submitted in partial fulfilment of requirement for degree of
Bachelor of Science with Honours
Aquatic Resource Science and Management
Department of Aquatic Science
Faculty Resource Science and Technology
Universiti Malaysia Sarawak
2014
i
Acknowledgement
Alhamdulillah, grateful to ALLAH the Almighty I finally managed to complete this
project. Here, I would like to take an opportunity to express my gratitude and appreciation
to those who bring successful to the completion of my project. I would like to express my
most sincere thanks and appreciation to my supervisor, Dr. Khairul Adha A. Rahim, who
had shown the guidance, support, endurance, and also the enthusiasm. All of his advice and
guidance will not been forgotten until the rest of my life.
Special thanks especially to my parents, En. Shahruzzaman bin Darul Aman and
Pn. Noriza binti Ismail for helping me in every aspect especially for giving me the strength
and also financial support for completing the project. Not to forget, thanks to my siblings
for their unequivocal support. I am obliged to lab assistant En. Zulkifli Ahmad and En.
Nazri Latip for helping me during my field work. Not to forget, to master and PhD
students; Kak Fateh, Kak Jawahir, Abg Azizil, Abg Raymie for giving me the valuable
information regarding my project. I also take opportunity to thank my friends for helping
me during my field work; Che Nurul Ashikin, Ghafur Rahim and Fakihin Aqsa.
Lastly, I thank all my friends especially my housemates (Aery, Nad, Wani, Alyn)
and classmates for their constant encouragement. Without all of these helps, this project
wills never ever success. Thank you very much.
ii
Declaration
I hereby declare that this thesis is based on my original work except for quotations and
citations, which have been duty acknowledged. I also declare that it has not been
previously or concurrently submitted for any other degree at UNIMAS or other
institutions.
…………………………………………………………..
DIANA BAZILA BINTI SHAHRUZZAMAN (30004)
Aquatic Resource Science and Management
Department of Aquatic Science
Faculty of Resource Science and Technology
Universiti Malaysia Sarawak (UNIMAS)
iii
Table of Contents
Acknowledgement…...………………………………………………….. i
Declaration……………………………………………………….……… ii
Table of Contents……………………………………………………...... iii
List of Abbreviations…………………………………………………..... vi
List of Tables…………………...……………….……………………..... vii
List of Figures….…………………………………………………..…..... viii
List of Appendices……………………………………………………..... ix
Abstract/Abstrak.……………………………………………………......
1
1.0 Introduction and Objectives………………………………………….
2
2.0 Literature Review………..……………………………….…..………
2.1 Taxonomy of Horseshoe Crabs……………………………....
2.2 Classification of Horseshoe Crabs…………..……………....
2.3 Morphological Characteristics of Horseshoe Crabs……..….
2.3.1 Length-weight Relationship of Horseshoe Crabs...
2.4 Habitat and Distribution…………………………….……....
2.4.1 Correlation between Sediment Particle and
Distribution of Horseshoe Crabs……………..…………..
2.5 Life Cycle of Horseshoe Crabs……………….………….…..
4
4
5
6
8
8
10
iv
2.6 Feeding Habits of Horseshoe Crabs……………………..…..
2.7 The Epibionts of Horseshoe Crabs…………………………..
2.8 Economical Values of Horseshoe Crabs……………….……
2.9 Threats to Horseshoe Crabs…………………….………..…..
2.10 Current Status of Horseshoe Crabs…….…………………...
10
12
12
13
14
15
3.0 Materials and Methods………………………………….……………
3.1 Study Site...……………………………………..……………
3.2 Field Analysis………………………………………………..
3.2.1 Field Work…………………………………………
3.2.2 Data collection.……………………...……………..
3.3 Data Analysis……………...…………………………………
3.3.1 Lab Analysis...……………………………………..
3.3.1.1 Total Organic Matter…………………....
3.3.1.2 Particle Size Analysis……..…………….
3.4 Descriptive Analysis…………………………………………
16
16
18
18
19
20
20
20
20
22
4.0 Results……………………………………………………………….
4.1 Horseshoe Crab Distribution and Composition……….…….
4.2 Length-weight Relationship of Horseshoe Crabs..………....
4.3 Particle Size Analysis………...…...…………………………
23
23
26
31
v
4.4 Physico-chemical Parameter Analysis……..………………..
33
5.0 Discussion……………………………………………………………
35
6.0 Conclusion and Recommendations..…………………………………
43
7.0 References……………………………………………………………
45
8.0 Appendices…………………………………………………………... 54
vi
List of Abbreviations
ANOVA
cm
CO2
DO
g
g/L
GPS
H2O2
IUCN
km
m
mL
mm
mg/L
µm
NaPO3
p.
ppt
PSA
SD
Sg.
SYSTAT
T
TOM
UNIMAS
Ver.7
Analysis of Variance
Centimetre
Carbon dioxide
Dissolved oxygen
gram
Gram per litre
Global position system
Hydrogen peroxide
International Union for Conservation of Nature
kilometre
Metre
Millilitre
Millimetre
Milligram per litre
Micrometre
Sodium hexametaphosphate
page
Parts per thousands
Particle Size Analysis
Standard deviation
Sungai (river)
System Statistics
Transect
Total Organic Matter
Universiti Malaysia Sarawak
Version 7
vii
List of Tables
Page
Table 3.1
The coordinate for three stations established in
Asajaya mangrove forest
16
Table 4.1 Species distribution of horseshoe crabs in
Asajaya mangrove forest
24
Table 4.2
Total length and total weight relationship of total
horseshoe crabs
28
Table 4.3
Total length and total weight relationship of T.
gigas species
28
Table 4.4
Total length and total weight relationship of C.
rotundicauda species
28
Table 4.5
The particle size distribution of sediments at
each stations in Asajaya mangrove forest
32
Table 4.6
Mean value of pore water analysis at all
sampling points
34
Table 4.7
One-way ANOVA show the significance
different between physico-chemical parameter at
all sampling points
34
viii
List of Figures
Page
Figure 2.1 Classification of horseshoe crabs family up to family
level
4
Figure 2.2 Distinguishing morphological characteristics of the
four species extant horseshoe crabs
5
Figure 2.3 External features of the horseshoe crab
6
Figure 2.4
The features of male and female of horseshoe crabs
7
Figure 2.5 The distribution of horseshoe crabs in the world
9
Figure 3.1 The map of study site – Asajaya, Kuching, Sarawak
17
Figure 3.2 The transect line in study site
18
Figure 4.1
The number of horseshoe crabs caught according to
species established at three stations of Asajaya
mangrove forest
24
Figure 4.2
The number of horseshoe crabs caught according to
their sex in Asajaya mangrove forest
25
Figure 4.3
The percentage of sex by (a) C. rotundicauda and (b)
T. gigas species at Asajaya mangrove forest
25
Figure 4.4
The mean length and weight of total horseshoe crabs
in Asajaya mangrove forest
27
Figure 4.5
Total length and total weight relationship of
horseshoe crabs
27
Figure 4.6
The linear relationship between total length and total
weight of T. gigas species
29
Figure 4.7
The linear relationship between total length and total
weight of C. rotundicauda species
29
Figure 4.8 The relationship between length and weight of
horseshoe crabs by species and sex
30
Figure 4.9 The particle size analysis of sediment at each station
in Asajaya mangrove forest
32
ix
List of Appendices
Page
Appendix A The Wenworth grain size scale for sediments
56
Appendix B IUCN Red List of Threatened Species
57
Appendix C
The picture of male and female ventral view 58
Appendix D The measurement data of species collected in
Asajaya Laut
59
Appendix E The measurement data of species collected in
Jemukan
59
Appendix F The measurement data of species collected in
Sadong Jaya
60
Appendix G The data of physico-chemical parameter
collected in Asajaya Laut
62
Appendix H The data of physico-chemical parameter
collected in Jemukan
62
Appendix I The data of physico-chemical parameter
collected in Sadong Jaya
63
Appendix J The data of particle size analysis in Asajaya Laut
63
Appendix K The data of particle size analysis in Jemukan
64
Appendix L
The data of particle size analysis in Sadong Jaya
64
1
Distribution and abundance of horseshoe crabs in Asajaya mangrove forest
Diana Bazila binti Shahruzzaman
Aquatic Resource Science and Management Programme
Faculty of Resource Science and Technology
Universiti Malaysia Sarawak
ABSTRACT
A study on the distribution and abundance of horseshoe crabs was carried out at Asajaya mangrove forest,
Sarawak. There were 52 individuals of horseshoe crab had been caught in three stations established; Asajaya
Laut (n=8), Jemukan (n=14), and Sadong Jaya (n=30). There were two species identified which were
Carcinoscorpius rotundicauda (n=31) and Tachypleus gigas (n=21) which come from family Tachypleine.
The mean length and mean weight of total horseshoe crabs caught was 25.89 6.14 cm, 150.28 76.54 g and
28.31 9.57 cm, 330.33 231.33 g for male and female respectively. The length-weight relationship for both
horseshoe crab caught showed a positive correlation (r=0.572). However, the length-weight relationship for
male T.gigas (r=0.725) and female C.rotundicauda (r=0.284) showed negative correlation. The sediment
analysis showed the highest contained of sediment was silt at all sampling sites and chi-square test showed
there were a significance difference (P<0.05) between the grain size of sediments and distribution of
horseshoe crabs. The physico-chemical analysis was done by using one-way ANOVA and showed
significance difference (P<0.05) for all parameters studied (Temperature, dissolved oxygen, pH and salinity).
Hence, the environmental variables (sediments and physico-chemical parameter) were important for
distribution and abundance of horseshoe crabs.
Keywords: Horseshoe crab, Carcinoscorpius rotundicauda, Tachypleus gigas, Length-weight relationship,
Environmental variables
ABSTRAK
Kajian ke atas taburan dan kelimpahan belangkas telah dijalankan di hutan bakau Asajaya, Sarawak.
Terdapat 52 individu belangkas yang ditemui daripada tiga stesen yang dikaji; Asajaya Laut (n=8), Jemukan
(n=14) dan Sadong Jaya (n=30). Terdapat dua spesis yang ditemui iaitu Carcinoscorpius rotundicauda
(n=31) dan Tachypleus gigas (n=21) yang berasal dari keluarga yang sama iaitu Tachypleinae. Purata
panjang dan berat belangkas yang ditangkap ialah 25.89 6.14 cm, 150.28 76.54 g dan 28.31 9.57 cm,
330.33 231.33 g untuk jantan dan betina masing-masing. Hubungan panjang-berat untuk dua spesis ini
menunjukkan pertumbuhan yang positif (r = 0.572). Walau bagaimanapun, terdapat hubungan panjang-
berat yang negatif untuk T. gigas jantan (r = 0.725) dan C. rotundicauda betina (r= 0.284). Analisis
sedimen menunjukkan bahawa kandungan kelodak adalah yang tertinggi untuk semua tapak persampelan
dan khi-kuadrat analisis menunjukkan terdapat perbezaan yang signifikan (P<0.05) di antara saiz butiran
sedimen dan taburan belangkas. Analisis fiziko-kimia telah dilakukan dengan menggunakan ANOVA satu
jalur dan hasilnya menunjukkan terdapat perbezaan yang signifikan (P<0.05) untuk semua parameter yang
dikaji (Suhu, DO, pH dan kemasinan). Oleh itu, pemboleh ubah alam sekitar (sedimen dan parameter fiziko-
kimia) adalah penting bagi taburan dan kelimpahan belangkas.
Kata kunci: Belangkas, Carcinoscorpius rotundicauda, Tachylpeus gigas, Hubungan panjang-berat,
Pemboleh ubah alam sekitar
2
1.0 Introduction and Objectives
Mangrove covers about 174, 000 hectares and occupies about 60% of 800 km length of
coastline at Sarawak (Nyanti et al., 2012). Khairul Adha (2000) stated that the ‘mangrove
area in Sarawak includes sheltered coastlines and estuaries of Kuching Division, Sri Aman
Division, Rajang Delta and Limbang Division’. Mangrove areas in Sarawak are the least
being distributed (Ashton et al., 2003) and provide the sheltered for most species like
horseshoe crab (Tomlinson, 1986; Han, 2011).
Horseshoe crab is one of the unique creatures in the world that could survive in
mangrove area (Tomlinson, 1986) as they have ability to cope with limited oxygen supply
(Sekiguchi and Shuster, 2009). Horseshoe crabs are marine arthropod which is also known
as ‘belangkas’ among Malaysian. Horseshoe crabs are known as ancient animal group and
often referred as living fossils (Heard, 2001; Chatterji and Abidi, 2004; Sekiguchi and
Shuster, 2009; Hu et al., 2011; Yap et al., 2011). Horseshoe crabs have been live before
the Jurassic period which is during Ordovian period in Palaeozoic era (Rudkin and Young,
2009). According to Yap et al. (2011), they are evolving from trilobites and still sustain
their characteristics for more than 450 million years.
Despite of name, horseshoe crabs are always being mistaken to be under crab’s
family (Heard, 2001; Hu et al., 2009; Rozihan and Ismail, 2012). Horseshoe crabs are not
true crab since they are not having five pairs of legs and a pair of claws like any other
crabs. According to Rozihan and Ismail (2012), horseshoe crabs are more closely related to
spiders, ticks and scorpions than to crabs. Hence, they are classified as subphylum
chelicerata.
3
There are four species of horseshoe crabs that can be found recently in the world
which are Tachypleus tridentatus, T. gigas, Carcinoscorpius rotundicauda and Limulus
polyphemus (Heard, 2001; Hu, 2011). All four species have different distribution which
based on their adaptation with the environmental factors such as salinity, temperature and
dissolved oxygen (Chatterji and Abidi, 2004).
A lot of studies have been done about the distribution and abundance of horseshoe
crabs especially at Delaware Bay on American species which is L. polyphemus such as
Botton and Ropes (1987), Botton (2000), Dietl et al. (2000), Smith et al. (2002), Rutecki et
al. (2004), Sweka et al. (2007), Medina and Tankersley (2010), Kasinak et al. (2011) and
Jane (2012). However, the study of distribution and abundance on horseshoe crabs in
Asajaya mangrove forest, Sarawak is still unclear to date.
Thus, the present study was aim to:
(1) determine the distribution and abundance of horseshoe crabs in Asajaya
mangrove forest,
(2) study the relationship between the length and weight of horseshoe
crabs,
(3) study the type of physico-chemical parameters preferred by horseshoe
crabs, and
(4) determine the correlation between sediment analysis and distribution of
horseshoe crabs.
This study provided such information on distribution and abundance of horseshoe
crabs in Asajaya mangrove forest, Sarawak and would improve our understanding on how
to minimise the rate of extinction of these organisms.
4
2.0 Literature Review
2.1 Taxonomy of Horseshoe Crabs
As elaborated in Lewbart (2012), the taxonomy of the horseshoe crabs shown in Figure
2.1.
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Meristomata
Subclass: Xiphosura
Order: Xiphosurida
Suborder: Limulina
Superfamily: Limulacea
Family: Limulidae
Limulus polyphemus (Linnaeus 1758)
Family: Tachypleinae
Tachypleus tridentatus (Leach 1819)
Tachypleus gigas (Muller 1785)
Carcinoscorpius rotundicauda (Latreille
1802)
Figure 2.1: Classification of horseshoe crab family up to family level (Adapted from Lewbart, 2012)
5
2.2 Classification of Horseshoe Crabs
Horseshoe crab can be divided into four species. According to Sekiguchi and Shuster
(2009), the morphology characteristics can be used to differentiate these four species;
frontal margin, frontal view, second prosoma appendage, third prosoma appendage, telson
(cross section), genital operculum and marginal spines as shown in Figure 2.2.
Figure 2.2: Distinguishing morphological characteristics of the four species of extant horseshoe
crabs adapted from Sekiguchi & Shuster (2009)
Among these four species, C. rotundicauda is the smallest species with average of
18 cm carapace (Fiona, 2004; Hu et al., 2011; Yap et al., 2011). C. rotundicauda can be
confused with T. gigas by looking at their frontal margin shape. However, both of them
can be differentiate by their telson in which C. rotundicauda has rounded and smooth
telson (Yap et al., 2011) while T. gigas have triangular telson.
6
2.3 Morphological Characteristics of Horseshoe Crabs
Up to date, the morphological study of horseshoe crabs had been done extensively by
many researchers. Fahrenbach (1981) and Walls et al. (2002) done research on Limulus
polyphemus, while, Yan et al. (2002) and Chiu and Morton (2010) were studied the Asian
horseshoe crabs. Based on Walls et al. (2002), horseshoe crabs have exoskeleton structures
which can be divided into three sections which are anterior frontal prosoma, posterior
opisthosoma and telson.
Figure 2.3: External features of the horseshoe crab. A. Dorsal view. B. Ventral view (Adapted from
Lewbart, 2012)
The upper body of horseshoe crab is known as prosoma (head and thorax) contains
of six appendages (Figure 2.3). According to Lewbart (2012), the first appendage is known
as chelicerae and can be found ventrally on prosoma which is used for feeding. The other
five legs are used as walking legs. However, the first leg is also known as pedipalp.
Pedipalp can be used to differentiate between male and female (Lewbart, 2012). In female,
A B
7
the pedipalp are morphological and functional similar as other legs as shown in Figure 2.4.
However, in male, the pedipalp is modified for grasping the female during mating. In both
female and male, the first four pairs of walking legs include pedipalp are also known as
gnathobase (Heard, 2001; Lewbart, 2012). The fifth pair of walking legs is modified for
cleaning the gills and removes the mud during burrowing.
Figure 2.4: The feature of male and female of horseshoe crabs. A. Male with pedipalp. B. Female
with same walking legs like other legs. (Taken from Galiano, 2009)
The lower part of horseshoe crab is opisthosoma (abdomen). According to Lewbart
(2012), opisthosoma carries six pairs of biramous limbs that functional as both
reproduction and respiration. The first pair is used as reproduction while the other five
pairs are modified as gills. There are lot of book gills underside of each gill flap which are
used for gas exchange.
A B
8
2.3.1 Length-weight Relationship of Horseshoe Crabs
Length-weight relationship can be defined as a connection between the two variables
(Vijayakumar, 2000). The length-weight relationship not only provides the growth pattern
of horseshoe crabs but also act as indicator of the health status of horseshoe crab’s habitat
(Chatterji et al., 1994; Vijayakumar, 2000; Ahmad Dar et al., 2012; Ismail et al., 2011).
The high number of horseshoe crabs on that habitat indicates the healthier environment of
that area (Tan et al., 2012), hence it lead to well development growth of horseshoe crabs.
According to Ahmad Dar et al. (2012), the length-weight relationship involved three
factors which are length, weight and sex. Generally, the female will have larger weight and
longer length compared to male as great quantities number of eggs will be held within the
female’s body.
2.4 Habitat and Distribution
The distributions of horseshoe crabs are most abundance along Atlantic coast of North
America and Southeast Asian as shown in Figure 2.5. L. polyphemus which is known as
Atlantic horseshoe crab (Walls et al., 2002; Rozihan and Ismail, 2012) inhabit along
Atlantic coast of North America (Chatterji and Abidi, 2004; Cartwright-Taylor et al.,
2011). The remaining three species of horseshoe crabs distribute mostly in Southeast Asian
(Sekiguchi and Shuster, 2009; Cartwright-Taylor et al., 2011; Rozihan and Ismail, 2012).
According to Rozihan and Ismail (2012), T. gigas distribute in the shores of the Bay of
Bengal particularly along the coast of Drissa, India to Indo-China, North-Vietnam, Borneo
and Celebes, Indonesia. Rozihan and Ismail (2012) also claimed that T. tridentatus can be
found in Northern shores of Japan to the South of Vietnam and along the Western islands
9
of the Philippines. She also stated that C. rotundicauda can be found in Northern shores of
the Bay of Bengal to the Southern coast of Philippines.
Figure 2.5: The distribution of horseshoe crabs in the world (Taken from Dunlap, 1999)
Different species of horseshoe crabs may inhabit different types of habitats. For
example, Asian horseshoe crabs, C. rotundicauda prefer to live in the mangrove swamp
area (Chatterji and Abidi, 2004; Fiona, 2004; Cartwright-Taylor et al., 2011; Hu et al.,
2011). However, they can also be found in brackish estuaries, mouth of rivers (Yap et al.,
2011). T. tridentatus and T. gigas can be found in both sandy and muddy habitats
(Cartwright-Taylor et al., 2011). For Atlantic L. polyphemus, they can be seen in shallow
seas and continental shelves. However, Patil and Anil (2000) stated that the adult prefer to
live in moderately deep waters. They will migrate to these shallow water areas for breeding
as these locations have becoming the important sources of food for themselves and their
juveniles (Sekiguchi and Shuster, 2009).
10
2.4.1 Correlation between Sediment Particle and Distribution of Horseshoe Crabs
Distribution of horseshoe crabs depends on the type of sediments they inhabits. According
to Blott and Pye (2001), the type of sediment is the most important factor that indicates the
deposition and distribution of horseshoe crabs. According to Chatterji and Abidi (2004),
horseshoe crabs will regularly migrate depend on the character of the sediment.
There are sediments with gravel, sand, silt and clay (Wentworth, 1893). Sekiguchi
and Shuster (2009) claimed that horseshoe crabs are able to detect the features of beach as
they need to select spot for spawning. According to Patil and Anil (2000), the horseshoe
crabs choose the loosely packed sediments as their nesting site as it will be easier for them
to dig and deposit their eggs.
2.5 Life Cycle of Horseshoe Crabs
The study of the horseshoe crabs reproduction was carried out extensively by Brockmann
and Smith (2009), Hajeb et al. (2009), Sekiguchi and Shuster (2009), Yang et al. (2009),
Botton et al. (2010), Mattei et al. (2010), Sasson et al. (2012) and Rozihan et al. (2013).
According to Yang et al. (2009), life cycle of horseshoe crabs depend on environmental
conditions on their habitat. Horseshoe crabs undergo their spawning stage in the sandy
beaches (Sekiguchi & Shuster, 2009). The higher rate of spawning of horseshoe crab
occurs during three conditions which is night, new or full moon and also high tide (Heard,
2001; Sekiguchi & Shuster, 2009; Zaleha et al., 2012; Rozihan et al., 2013).
Brockmann (2002) stated that around three days before the full or new moon
occurred; the male trailing around the shorelines and waited for the female. The female
then will migrate to the nesting ground. The migration of the female is help by the water
current (Akbar John et al., 2012b). According to Saunders et al. (2010), female will attract
11
the male by releasing their pheromone. The male will detect their mate by two factors
which are chemical and visual (Walls et al., 2002). The male then clings to the female by
using their pedipalp for mating. The female will drag the male and dig the sand for their
nesting ground (Brockmann et al., 2000).
Female prefer to lay eggs in the loosely packed sediments in intertidal areas to
protect it from predator (Chatterji and Abidi, 2004). Furthermore, the nest must be at the
high spring tides for greatest development of their eggs as above and below of the level
may lead to the dry sediment and low oxygen content respectively (Brockmann et al.,
2000). According to Patil and Anil (2000), female will bury themselves to the level of eyes
during nesting until successful laying their eggs. Since the spawning occurred at the beach,
the burrowing will help them from the exposed coasts (Jackson et al., 2005).
After the female lays approximately 4, 000 of green eggs, the male will fertilize
them. The fertilization takes place outside of the body (external fertilization). The high
number of eggs is their life strategy as they leave will leave the nest after spawning (Heard,
2001). Once fertilization is done, the female will leave the nest and began to dig the next
nest for the nest spawning with other male (Patil and Anil, 2000).
The eggs will double in size after few days and outer layer will peel away causes
the eggs to be transparent. About two weeks after, the swimming arthropod larvae will be
hatch from the eggs (Dietl et al., 2000; Zadeh et al., 2009). These juveniles will appear like
their adult. During high tide, they will bury themselves in the mud (Sekiguchi and Shuster,
2009). During low tide, they will emerge from the mud and feed in the pools.
At the stage of juvenile, they will undergo process moulting which is the shed of
their exoskeleton to reach a sexual maturity of adult (Faizul et al., 2011). The exoskeleton
will then replace by the new one as during this process they will pump in water to expand
12
the new shell. The new shell will be hardened in only 24 hours. Normally, male will take
16 times moult while female take 17 times moult to reach adult (Heard, 2001).
As they grow into adult, they will move to the deeper water. Every year during
spawning season, those adult will migrate back to the sandy beaches and repeat their life
cycle until their death.
2.6 Feeding Habits of Horseshoe Crabs
Horseshoe crabs are benthic feeders (Heard, 2001; Botton, 2009; Hu et al., 2011). The diet
are varies according to their age. Adults are normally omnivore and able to feed higher in
food web such as bivalves, crustaceans and polychaetes (Carmichael et al., 2004; Botton,
2009). Horseshoe crab used chemoreceptor which is a tiny hair on spiny projections around
its mouth to detect their prey. Horseshoe crabs are using their first pair of legs known as
chelicerae to crush the food as they are have none of jaws to chew it. They also have
gizzards with sand and gravel to help them grind their food (Heard, 2001; Botton, 2009).
2.7 The Epibionts of Horseshoe Crabs
The wide surfaces area of carapace causes the presence of epibionts (Botton, 2009). The
epibionts attached are green algae, oysters, mussels, tunicates, diatoms, barnacles,
gastropods and flatworms (Botton, 2009; Patil and Anil, 2010; Tan et al., 2011). However,
among all these epibionts, barnacles are the most dominant epibionts attached on
horseshoe crabs (Tan et al., 2011). According to Tan et al. (2011), L. polyphemus carries
many organisms on their carapace and so known as ‘walking museum’.
13
The presences of epibionts cause the damage to horseshoe crabs as epibionts may
inhabit the unsuitable place on carapace (Tan et al., 2011). For example, the epibionts that
inhabit the lateral eyes may result the loss vision of horseshoe crabs. Hence, the lack of
vision will limit the ability of horseshoe crabs to find their partner for spawning purpose.
Despite the fact that female had wider carapace, the female had less epibionts
attached on their carapace compared to male (Patil and Anil, 2000). According to Tan et al.
(2011), the difference number of epibionts attached is due to the mating and nesting
behaviour. The male horseshoe crabs will migrate to the beach during spawning periods
regularly compared to female. Hence, the lighter colour and rougher carapace of male
horseshoe crabs will attract and increase the quantities of epibionts (Patil and Anil, 2000).
2.8 Economical Values of Horseshoe Crabs
Horseshoe crabs are similar to any other marine creatures which can give a lot of benefits.
The uniqueness of their blue blood is widely used in biomedical industry (Yang et al.,
2009). The biomedical applications had been studied by Akbar John et al. (2012a), Heard
(2001), Walls et al. (2002), Hurton (2003) and Yang et al. (2009). According to Heard
(2001), this activity was started by The Food and Drug Administration of United States in
1997. They are using the Limulus Amoebocyte Lysate (LAL) which purified from the
horseshoe crab blood to detect the pathogenic endotoxins in the medical products (Heard,
2001; Hurton, 2003). Hence, these products will be free from the contaminating
endotoxins. In addition, Mattei and Beekey (2008) stated that, in United States, the test of
bacterial contamination must be done by using LAL to all medical products that will be
inserted into the human body. If the product was believed to be contaminated, it must be
