Faculty of Resource Science and Technology
THE MORPHOLOGY AND GUT CONTENT STUDY OF THE
HORSESHOE CRABS IN SELECTED COASTAL WATER OF SARAWAK
Nurul Atikah Binti Mat Jusoh
Bachelor of Science with Honours
(Aquatic Resource Science and Management)
2014
The Morphology and Gut Content Study of the Horseshoe Crabs
in Selected Coastal Water of Sarawak
Nurul Atikah Binti Mat Jusoh
The dissertation is submitted in partial fulfilment of requirement for the degree of Bachelor
Science with Honours in Aquatic Resource Science and Management
Faculty of Resource Science and Technology
Universiti Malaysia Sarawak
2014
ACKNOWLEDGEMENT
Firstly, let say Alhamdulillah because finally I could finish my final year’s project on the
title “The morphology and gut content study of the horseshoe crabs in selected coastal
water of Sarawak”.
Firstly, I would like to thank my supervisor, Dr. Samsur bin Mohamad for his guidance,
constructive comments and sharing knowledge to help me finish my projects. With the
guidance from my supervisor, I could finish my project successfully on time.
Besides that, I would like to acknowledge the lab assistant, which are En. Nazri, and En.
Zaidi, for their helps during my fieldtrip and not to forget, the PhD student, Ms. Jawahir
for sharing information during the lab work session. I also would like to thanks my fellow
labmates Amni, Ghafur and Fakihin for the suggestion and contribution of ideas along the
progress of the project. In the other hand, thanks to UNIMAS for all the facilities provided
in the lab that make me to able finish my project experiment. Lastly, thanks to all my
classmates, which direct or indirectly involved for all the encouragement and support given.
Last but not least, I would like to thanks my parents Mat Jusoh bin Abdullah and Fatimah
binti Daud which nonstop give me support and encouragement to finish the project within
the duration given. Without help and encouragements from all of them, this project would
not possible.
I
DECLARATION
No portion of the work referred to this dissertation has been submitted of an application for
another degree of qualification of this or any other university or institution of higher
learning.
________________________
Nurul Atikah Binti Mat Jusoh
Aquatic Resource Science and Management
Department of Aquatic Science
Faculty of Resource Science and Technology
Universiti Malaysia Sarawak
II
Table of Contents
Pages
Acknowledgement………………………………………………………….………….. I
Declaration…………………………………………………………………………….. II
Table of Contents……………………………………………………………………... III
List of Abbreviations…………………………………………………………………... V
List of Tables………………………………………………………………….…...…… VI
Lists of Figures………………………………………………………………….…...…. VII
Lists of Appendices…………………………………………………………………….. VIII
Abstract………………………………………………………………………………..…...1
1.0 Introduction ……………….……………………………………………………….…..2
2.0 Literature Review……………………………………………………………………....5
2.1 Morphology of the Horseshoe Crabs…………...……………………......…….5
2.2 Gut Content and Toxicity of the Horseshoe Crabs..……………...……………10
2.3 Important of the Horseshoe Crabs...……………………………….…...…...…13
3.0 Materials and Methods…………………………………………………….………..…15
3.1 Field Work………………………………………………………….……........15
3.1.1
Study Site……………………………………………..….…...…...15
3.1.2
Field Sampling………………………………………..…..….……17
3.2 Laboratory Work…………………….…………………………..…….…..…..18
3.2.1
Morphological Study………………………………..……......……18
3.2.2
Gut Content Analysis………………………………..….............…19
4.0 Results and Discussion…………………………………………………..………...…..20
4.1 Morphology of the Horseshoe Crabs..………………………………….....…..20
4.2 Morphometric Analysis………………………………………………...…..…28
4.3 Gut Content of Horseshoe Crabs……….…………………….…………..…..40
4.3.1
Sibu Laut…………………………………………..………..……..40
4.3.2
Kampung Pasir Putih……………………………..………….…....41
III
5.0 Conclusion……………………………………………………………..……….……43
5.1 Recommendation…………………………………………………………….43
6.0 References…………………………………………………………..……………….44
7.0 Appendices…………………………………………………………….…………….47
IV
List of Abbreviations
Abbreviations
Description
CW
Carapace Width
g
gram
GPS
Global Positioning System
mm
millimetre
n
Total number
ng/ml
nanogram/ millimetre
Tel.L
Telson Length
TL
Total Length
TTX
Tetrodotoxin
TW
Total Weight
%
percentage
V
List of Tables
Table 1
Location and general description of the selected
Pages
15
sampling sites in Sarawak
Table 2
Mean of the different body measurements with their
29
standard deviation of T. gigas
Table 3
Mean of the different measurements with their
30
standard deviation of C. rotundicauda
Table 4
Comparison of mean and standard deviation of C.
rotundicauda from Sarawak and Johor
VI
38
Lists of Figures
Figure 1
Distinguish morphological characteristics of the horseshoe
Pages
7
crabs
Figure 2
Sampling sites of the horseshoe crab at selected area in
16
Sarawak
Figure 3
The appearance of the horseshoe crabs
21
Figure 4
Morphology of the horseshoe crabs at dorsal and ventral view
22
Figure 5
The pictures of morphological characteristics of T. gigas that
23
were used for the identification
Figure 6
The pictures of morphological characteristics of C.
24
rotundicauda that were used for the identification
Figure 7
The female and male horseshoe crabs
26
Figure 8
The appendages that distinguish between female and male
26
horseshoe crabs
Figure 9
The number of claw present at first and second appendages of
27
male horseshoe crabs
Figure 10
The colour of compound eye
27
Figure 11
Comparison of mean and standard deviation in total weight
31
between 3 sampling sites
Figure 12
The present of scar on the opithosoma of the horseshoe crabs
33
Figure 13
Variation in size of the horseshoe crabs
33
Figure 14
Comparison of mean different body parts T. gigas from Sibu
34
Laut
Figure 15
Comparison of mean different body parts T. gigas from
35
Maludam
Figure 16
Comparison of mean different body parts T. gigas from
37
Kampung Pasir Putih
Figure 17
The gut content of the horseshoe crab at Sibu Laut
41
Figure 18
The gut content of the horseshoe crab at Kampung Pasir Putih
42
VII
List of Appendices
Pages
Appendix 1
Types of the horseshoe crab found at selected
area in Sarawak
47
Appendix 2
Dietary items observed under stereo microscope
48
Appendix 3
Data from first sampling at Maludam
50
Appendix 4
Data from second sampling at Sibu Laut
50
Appendix 5
Data from third sampling at Kampung Pasir Putih
51
VIII
The morphology and gut content study of the horseshoe crabs
in selected coastal water of Sarawak
Nurul Atikah binti Mat Jusoh
Aquatic Resource Science and Management
Faculty of Resources Science and Technology
Universiti Malaysia Sarawak
ABSTRACT
This study was carried out to determine and document the morphological characteristics and also to identify
gut content of the horseshoe crabs in selected area of Sarawak. The sampling was done at selected coastal
water of Sarawak which are Maludam, Sibu Laut, and Kampung Pasir Putih. The location of each station was
recorded by GPS which Maludam (01° 39’ 50.7’’N, 111°01’ 15.5’’E), Sibu Laut (01° 41’ 18.2’’N,
110°12’08.9’’E) and Kampung Pasir Putih (01° 39’ 49.1’’N, 110°28’ 29.8’’E).For the morphological study,
the characteristics of the sample (i.e body segmented, total length, carapace width, and telson length) were
measured, recorded and described. Based on characteristics analysed, the sample have been identified as T.
gigas and C. rotundicauda. The total numbers of the sample that was used for this study is 119 individuals
for morphological study and 22 sample for gut content study of the horseshoe crab. Each species can be
differentiated as each species have a different morphological characteristics. The horseshoe crabs is an
omnivorous animals which feed on algae, polychaete, plant materials and molluscs, however it most
preferred mollusc such as bivalve and gastropod compared to others.
Keywords: morphological, body segmented, horseshoe crabs, omnivorous, and molluscs.
ABSTRAK
Kajian ini telah dijalankan untuk menentukan dan mendokumenkan ciri-ciri morfologi dan juga untuk
mengenalpasti kandungan usus belangkas di kawasan terpilih di Sarawak. Persampelan telah dijalankan di
pesisir pantai yang terpilih di Sarawak seperti Maludam, Sibu Laut dan Kampung Pasir Putih. Lokasi setiap
stesen direkodkan oleh GPS yang Maludam (01 ° 39 '50.7'' N, 111 ° 01' 15.5'' E), Sibu Laut (01 ° 41 '18.2'' N,
110 ° 12'08 .9'' E) dan Kampung Pasir Putih (01 ° 39 '49.1'' N, 110 ° 28' 29.8'' E). Untuk kajian morfologi,
ciri-ciri sample (iaitu segmen badan, jumlah panjang, lebar karapas, dan panjang telson diukur, direkodkan
dan diterangkan. Berdasarkan ciri-ciri yang dianalisis, sampel telah dikenal pasti sebagai T. gigas and C.
rotundicauda. Jumlah bilangan sampel yang digunakan untuk kajian ini adalah 119 individu untuk kajian
morfologi dan 22 sampel untuk kajian kandungan usus belangkas. Setiap species boleh dibezakan kerana
setiap species mempunyai ciri-ciri morfologi yang berbeza. Belangkas adalah haiwan omnivor yang
memakan alga, polychaete, bahan-bahan tumbuhan dan moluska, walau bagaimanapun, belangkas lebih
mengemari moluska seperti kerang and gastropod berbanding dengan yang lain.
Kata kunci: morfologi, badan segmen, belangkas, omnivor, dan moluska.
1
1.0 Introduction
Horseshoe crabs is one of the ancient animals that already exist in the world more than
millions years ago (Sekiguchi & Shuster, 2009). Horseshoe crabs are classified in the
phylum Arthopoda and class Merostomata because horseshoe crabs have legs that
surrounded the mouth and five pairs of variously modified legs plus one pairs small
chelicerae (Vijayakumar, 2000; Sekiguchi & Shuster, 2009).
There are four species of horseshoe crab that exist in the world which are
Tachypleus gigas, Tachypleus tridentatus, Carcinoscorpius rotundicauda and Limulus
polyphemus. However, according to the previous study done by John et al. (2012) there
are only three species of horseshoe crabs that inhabit Malaysian coast which are T.
gigas, T. tridentatus and C. rotundicauda. Another species of horseshoe crab is L.
polyphemus which is mainly found at the Atlantic coast of North America (Ismail et al.,
2011). According to Chatterji and Noraznawati (2009) the distribution and habitat are
vary between species.
Three species which are T. gigas, C. rotundicauda and T.
tridentatus can be found in Asia mostly western Pacific Ocean from India up to Japan
and south to Malaysia and Indonesia (Cartwright-Taylor et al., 2011; Fish & Wildlife
Research Institute, 2007). Another species is L. polyphemus which can be found
especially Atlantic coast of North America and gulf coast from Maine to the Yucatan
Peninsula in Mexico (Cartwright-Taylor et al., 2011)
Mainly horseshoe crabs can be found at the intertidal zone of coastal area.
According to Carmichael et al. (2003), horseshoe crabs prefer to inhabit near to inshore
estuaries which is less than 30 metres of water from the continental shelf. However,
different species prefer different habitat. Cartwright-Taylor et al. (2011) revealed that T.
2
gigas and T. tridentatus prefer sandy to muddy habitat, unlike C. rotundicauda which
only prefer muddy area mostly brackish areas.
According to Hussain et al. (2009), meristic and morphometric analysis can be
used to differentiate the species that closely related species and have a huge similarity
indices of various parameter. In Sarawak, there are limited data that available on the
length-weight relationship, meristic and morphometric characteristics of horseshoe
crabs. Srijaya et al. (2010) described that morphology of the horseshoe crabs are look
same when observed roughly without doing the morphology analysis.
Morphometric studies were used to compare the quantitative measurements
different part of horseshoe crabs and the data were analysed statistically to observe the
differences in their morphometric structures (Srijaya et al., 2010). Thus to explain the
differences in measurements of the structure the allometric analysis were carried out.
Srijaya et al. (2010) stated that differences of various measurements horseshoe crabs
between different habitats can be evaluate using allometric analysis.
This study were conducted at three different places at Sarawak water, Sibu Laut,
Maludam and Kampung Pasir Putih for the morphological characteristics whereas for
the gut content analysis only two sampling sites were considered which are Sibu Laut
and Kampung Pasir Putih. There are limited data on gut content and morphology of the
horseshoe crabs in coastal area of Sarawak. Through this study the awareness among
the local people can be created especially for the public that interested in hatchery and
aid conservation of natural population. For those that interested to culture the
horseshoe crabs they need to know on how to measure the growth and understand the
diet composition that yields the highest rates of growth and survival.
3
The objectives of this study were:
1) To determine and document the morphological characteristics of the horseshoe
crabs in selected coastal area of Sarawak.
2) To identify the gut content of the horseshoe crabs from the selected coastal area of
Sarawak.
4
2.0 Literature Review
2.1 Morphology of the Horseshoe Crabs
Horseshoe crabs appearance remains unchanged over 350 million years ago thus it is
known as evolutionary survivors. All four species of the horseshoe crabs have almost
similar physical appearances among it. The morphology of the horseshoe crabs can be
differentiating into three main sections which are prosoma, opithosoma and telson.
Another name for the prosoma is head whereas for the opithosoma is central area and
telson well known as tail. Besides that, horseshoe crabs get it names from it prosoma as
it looked like shape of the horse’s shoe.
Under the prosoma consist of organ systems and 5 pairs of appendages of
variously modified appendages for its specific function. The example of organ under
prosoma is brain. Fish and Wildlife Research Institute (2007) stated that the smallest
appendages which anterior-most appendages also known as chelicerae play important
roles in feeding process as it picked the food and passes to the mouth. Five pairs of
appendages are divided into 2 which middle four pairs of appendages are called
walking legs where at the end of each appendages have small claws and last pair of
appendages also known as pusher legs. At the end of pusher leg are brush-like end
which function for movement of the horseshoe crabs on the land and for digging during
spawning and searching the food (Fish & Wildlife Research Institute, 2007).
The prosoma and opithosoma are connected by the simple hinge joint (Sekiguchi
& Shuster, 2009). Underside of the opithosoma consists of respiratory and reproductive
structures such as book gills, muscles groups and genital pores. Fish and Wildlife
Research Institute (2007) stated that the first gills of the horseshoe crabs plays important
roles to protect other gills and cover the genital pore which sperm or eggs are releases
5
during mating. The first gill has been modified into operculum to accomplish it
function. The five other pairs of gills involve in the respiration process as it keep
oxygenated water flowing around them by continuously moves the books gills (Fish &
Wildlife Research Institute, 2007). U. S. Fish and Wildlife Service (2006) stated that
horseshoe crabs can stay outside of water for the four day if the gill is still moist. The
alternatives done by the horseshoe crabs in order to conserve the water until the tide are
rises back whether they bury themselves in sand or fold themselves in half (U.S. Fish &
Wildlife Service, 2006). The swimming process also involves the roles of book gills
where the book gills act as the paddle to assist in swimming.
The presence of telson at third section to help the horseshoe crabs to flip itself
over in case the body turn it over. According to the Fish and Wildlife Research Institute
(2007) it was connected by the ball and socket joint to the abdomen so that it can move
the telson in multiple planes. U.S. Fish and Wildlife Service (2006) stated that at five
pairs of legs have an impressive array of spiny mouth bristles to maneuver food items
such as soft shelled clams into their centrally located mouth because they do not have
jaws or teeth. Besides that, the walking movement must be stimulated in order to chew
the foods.
Horseshoe crabs have 2 large compound eyes on it upper carapace however; there
also additional eyes belong to horseshoe crabs which in total eyes of the horseshoe
crabs are 10. The compound eyes of horseshoe crab can detect movement but image that
form are not clear (Gerhart, 2007). As described by Gerhart (2007) another 8 eyes of
horseshoe crab which are 2 median ocelli, 2 rudimentary lateral eyes, 1 endoparietal eye,
2 ventral eyes, 1 set of receptor along the telson. Median ocelli can form image and
have a lenses that located near to the front carapace and sensitive to the ultraviolet light
(Barlow & Powers, 2003). Gerhart (2007) also stated that near to compound eye are
6
rudimentary eyes located, whereas endoparietal eye are located between median ocelli
and underside of the carapace near to the mouth consist of ventral eyes. The
rudimentary eyes, endoparietal eye and ventral eyes only can detect light but do not
form an image (Gerhart, 2007).
According to Sekiguchi and Shuster (2009) the sex of the horseshoe crabs can be
determine based on it morphology. Male horseshoe crabs has a ‘boxing-glove’
appendages on it first and second appendages while female have an appendages
‘scissor-like’ on it first and second appendages. The function of the boxing glove
appendages on male horseshoe crabs to grasp the female during the spawning process.
The male will grasp at the opithosoma of female horseshoe crabs and cling to female.
So when female move it will bring along the male horseshoe crab. Sekiguchi and
Shuster (2009) stated that the boxing gloves will form after several times undergo the
molting process.
Figure 1: Distinguish morphological characteristics of the horseshoe crabs (Sekiguchi & Shuster,
2009).
7
Another morphology characteristic that can be used to determine sex is by
observing it genital operculum (Sekiguchi & Shuster, 2009). The genital operculum for
male normally has genital papillae with hard raised bump whereas genital operculum of
the female is softer bump gonopore with silt, because female produce egg and lay egg.
In this study only focussed on two species which are T. gigas and C. rotundicauda.
Referring to the table of morphology characteristics of horseshoe crab by Sekiguchi and
Shuster (2009), the male horseshoe crabs between species can be differentiated by
observing the numbers of claw present at it appendages, frontal view, cross section of
tail and genital operculum. T. gigas has only 1 claw for it appendages especially first
and second appendages. However C. rotundicauda have 2 claw present at it first and
second appendages.
The frontal view of T. gigas more curve compare to C.
rotundicauda for the male horseshoe crab (Sekiguchi & Shuster, 2009).
For the female horseshoe crabs, it can be differentiated between species by
observing the marginal spines and cross section of the telson (Sekiguchi & Shuster,
2009). The arrangement of the spine is different between these 2 species. Female T.
gigas have a 3 uniform larger marginal spine at the upper part compare to the 3 uniform
small spines at the lower part. In contrast, the female C. rotundicauda have a similar in
their size of spine from the upper part to the lower part. According to Sekiguchi and
Shuster (2009) both male and female for each species have the same cross section
which T. gigas have a triangular cross section of tail or telson whereas C. rotundicauda
have a rounded cross section of telson.
The habitat for the horseshoe crabs always at the shallow water and recent
geologic history stated that the breeding and nursery ground for the horseshoe crab take
places is the estuaries. According to Emily (2011) throughout their lifetimes, horseshoe
crab makes use of three different habitats which are near to bay, intertidal sand flat and
8
deeper water. During spawning season, the horseshoe crabs will go sandy beach area
that inside the bay or coves to avoid rough water in order to protect their eggs. The
characteristics of the area must be well oxygenated sediments, porous, and near to large
intertidal sand flats. The juveniles mainly will spend their first two years at intertidal
sand flats and once the reach maturity it will migrate to deeper water (Emily, 2011).
The horseshoe crabs have wide range of salinity that it can tolerate as low as 8-9
part per thousand and as high as full strength seawater and hypersaline conditions
(Sekiguchi & Shuster, 2009). Chatterji and Abidi (1993) also explained about the
speciality of the horseshoe crabs that can stand and tolerate with wide range of
temperature, submergence, dessication and salinity. With that speciality they can exist
in the world more than million years ago. According to the previous study by Chatterji
and Abidi (1993) the migration of horseshoe crabs normally take place during full moon
tide compare to the new moon tide and no migration for the breeding purposes and
activity during neap tides.
According to Gerhart (2007) the peak season for horseshoe crabs spawning are
different between region for example in Delaware Bay the peak is between mid-May
until mid- June.
9
2.2 Gut Content and Toxicity of the Horseshoe Crabs
Botton (1984) described the function and characteristics of chelicerae which plays
important roles to capture the foods and push into the mouth of the horseshoe crabs. In
order to grind the foods such as mollusc shells and other preys, the present of fortified
sharp spine at legs plays its roles to turns the foods into small pieces. The additional
grinding will occur at the gizzard after the food enter the mouth and passed through a
short oesophagus before reached at the muscular and chitinous gizzard (Botton, 1984).
John et al. (2012) stated that the common of the gut content found in C.
rotundicauda are bivalves, gastropods and polychaetes. According to Carmichael et al.
(2009) adult horseshoe crab most preferred bivalves, gastropods, marine algae,
crustaceans and polychaetes whereas juvenile’s horseshoe crab most preferred
crustaceans and polychaetes.
Besides that, the seasonal variation in food composition prefer by the horseshoe
crabs shows the main items prefer is molluscs especially gastropods (John et al., 2012).
The example of the gut content that was found in the gut content of L. polyphemus is
Gemma gemma which is thick shelled clam and slow growth and also two that rapidly
growth and thin shelled such as Mya arenaria and Mulinia lateralis (Botton, 1984).
In Thailand and Malaysia, there are several famous dishes based on eggs of
horseshoe crabs such as Yum Kai Meng Da in Thailand and ‘Asam Pedas’ and ‘Sambal
Tumis Belangkas’ in Malaysia. Bovornkitti and Kulkantrakorn (2004) stated that 125
cases have been reported at Chan Buri Hospital due to ingestion eggs of the horseshoe
crabs and cause poisoning to them. However only seven cases that have been published
in Thailand that related to the horseshoe crabs poisoning.
10
According to the Kanchanapongkul (2008) there are high in number of reported
cases in Thailand relating with tetrodotoxin (TTX) poisoning from 1994 until 2006 due
to ingestion of the eggs of C. rotundicauda horseshoe crabs which are 280 cases. There
is a cases at Kota Marudu, Sabah where there have been reported about the death one
person due to the consumed of horseshoe crabs as their delicacy (Che Nin et al., 2011).
There are 5 people that infected due to poisoning of consuming horseshoe crabs but
resulted in death of one person. The urine test was done for the entire victim and find
out there is highest concentration of TTX in the urine of deceased which is 93.4 ng/ml
while the victim survived consists of 1.3-17.3 ng/ml in their urine (Che Nin et al.,
2011).
The most common symptoms complaints by the patients are weakness, dizziness,
vertigo, nausea and vomiting due to ingestion eggs of the horseshoe crabs. There are
four stages of poisoning that can be refer for the tetrodotoxin poisoning which are stage
1, stage 2, stage 3 and stage 4 (Kanchanapongkul, 2008). Kanchanapongkul (2008)
described the symptoms and signs for the stage 1 are perioral and lingual numbness or
paresthesia, nausea and vomiting, whereas for the stage 2 usually the patient will have
numbness progresses markedly and motor paralysis of extremities. Parethesia can be
observing 10-45 minute after ingestion of the eggs (Centre for Disease Control &
Prevention, 1996). Blue Ridge Poison Centre (2008) elaborated more on parethesia
which initially it will affect the lips, mouth and tongue, and cause extremities.
Furthermore, the symptoms for stage 3 are progressive motor paralysis, bulbar
muscles paralysis and mostly the patient is conscious. The most critical stage is stage 4,
the patient may have respiratory failure, hypoxia, unconsciousness and hypotension
may occur, and also fixed and dilated pupils (Kanchanapongkul, 2008).
11
As elaborated by Kanchanapongkul (2008) the TTX compound is water soluble
and thus the effect of poisoning due to TTX depend on its amounts of toxin ingested.
Another property of TTX is heat stable and it can block the sodium conductance and
also neuronal transmission in skeletal muscles (Centre for Disease Control &
Prevention, 1996). Blue Ridge Poison Centre (2008) also stated that the TTX is not
damaged by the process of freezing.
The TTX can be found in the intestines, liver, and skin with high concentration for
some species such as molluscs, puffer fish and blue ringed octopus (Blue Ridge Poison
Centre, 2008). The cases of the horseshoe crabs poisoning still occur due to the some
inaccurate rumours among public such as non-toxic eggs will burst during cooking, the
poisonous and edible horseshoe crabs can be differentiate, the toxins contain in the eggs
of the horseshoe crabs can be destroyed by cooking and their mind-set about horseshoe
crab is always non-toxic as its previously safe to eat.
12
2.3 Important of the Horseshoe Crabs
Horseshoe crabs are benthic macrobenthos organism and they plays important role in
their ecosystem which acts as a predator for thin-shelled bivalves and prey for the
migratory shorebirds. The eggs of the horseshoe crabs provide the protein for the
migratory birds to migrate from one place to another place which is a long distance
migration (U.S Fish & Wildlife Service, 2006). The migratory birds feed on the eggs of
the horseshoe crabs once the female horseshoe crabs lay their eggs at the beaches.
According to Castro and Myers (1993) bird arrived at the beach synchrony with the
emerge of the horseshoe crabs from sea during high tide thus easier for the migratory
birds to eat the eggs of the horseshoe crabs as it know the exact place where the eggs
are buried by the horseshoe crabs. In facts, although the eggs are buried into sand by the
horseshoe crabs, but due to incoming of wave indirectly exposed the eggs from the
sand. As described by U. S Fish and Wildlife Service (2006) the example of migratory
birds that consume the eggs of the horseshoe crabs for their energy to fly long routes
such as Sanderlings, Dunlins and Ruddy Turnstones. The horseshoe crabs contribute
different way to the human and other organism in the ecosystem.
Chatterji and Abidi (1993) stated that the eyes of horseshoe crabs useful in the
understanding of the principle in developing and making of compass for navigation in
polar regions like Antartica as the magnetic compass cannot useful at the polar region. It
eyes can polarise light and the present of the crystal lining cones to concentrate it
tenfold. These adaptations are suitable to horseshoe crabs as their habitat at dark muddy
water and transluscent. Furthermore the scientist gets the idea in designing the solar
energy collector from the structure of eye horseshoe crabs (Chatterji & Abidi, 1993).
13
Besides that, horseshoe crabs also function as a host for epibiotic community such
sponges, flatworms, barnacles, mussels as they will attach to the carapace of the
horseshoe crabs as the free space is limiting thus the epibiont prefer the living substrata
as their host (Patil & Anil, 2000). However when the horseshoe crabs molts the
organism will stay at the old skeleton thus produce clean and new carapace of the
horseshoe crabs (Fish & Wildlife Research Institute, 2007). The attachment of the
epibiont on the carapace cause some advantage for the horseshoe crabs as it can be used
as a camouflage and protective value for the host (Patil & Anil, 2000). The example of
epibiont that attach on the carapace of the horseshoe crabs such as green mussels,
oysters, barnacles, tunicates and gastropods. According to Patil and Anil (2000),
barnacles are the most common epibiont that make carapace of the horseshoe crabs as it
host.
In medicine the horseshoe crabs also plays important function to detect the present
of bacteria in the blood or also known as bacterial endotoxin (Heard, 2001; Zaleha et
al., 2012). Besides that, horseshoe crabs also used in pharmaceutical and medical
devices industries to confirm and guaranteeing that product such as vaccines,
intravenous drugs, and medical devices are free from bacterial contamination (Eaton,
2011).
The blood of the horseshoe crabs contain cells that can react with the certain kinds
of disease causing bacteria. The famous Limulus Ameobocytes Lysate (LAL) is
extracted from the L. polyphemus to test the drugs that produce is free from those
harmful bacteria before the drugs been distributed to people. In other hands, LAL also
used to detect spinal meningitis and some cancer and also to test the sterility of
antibiotics and kidney dialyzers (Heard, 2001). Zaleha et al. (2012) stated that annually
LAL compound can contribute a billion dollar, such a big profit.
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