Surface Zooplankton Community Composition in Whale shark
(Rhincodon typus) Feeding Grounds Off Sogod Bay, Southern Leyte
during August 2013 to March 2014
by
PAUL MATTHEW L. MUNCADA
A research paper submitted to theDivision of Natural Sciences
and MathematicsUniversity of the Philippines VisayasTacloban
College, Tacloban City
As partial fulfillment of the requirementsfor the Degree ofB.S.
BIOLOGY
May 2014
Permission is given for the following people to have access to
this research:
Available to the general publicYes
Available only after consultation with author/adviserNo
Available only for those bound by confidentiality
agreementNo
Students signature:
Signature of Research Adviser:
This is to certify that this research paper, entitled: Surface
Zooplankton Community Composition in Whale shark (Rhincodon typus)
Feeding Grounds Off Sogod Bay, Southern Leyte during August 2013 to
March 2014 and submitted by PAUL MATTHEW L. MUNCADA to fulfill part
of the requirements for the Degree of Bachelor of Science in
Biology is hereby endorsed.
LENI G. YAP-DEJETOResearch Adviser
The Division of Natural Sciences and Mathematics (DNSM) accepts
this research paper in partial fulfillment of the requirements for
the Degree Bachelor of Science in Biology.
ROBERTO E. CAPONDNSM Chair
ACKNOWLEDGEMENT
I would like to express my deepest gratitude to all the people
who have guided me to achieve the accomplishment of this research:
to my adviser, Prof. Leni Yap-Dejeto, for suggesting and entrusting
this study to us. We would have never been able to make it if not
for her valuable advices and support throughout the study period
from the proposal up to the oral presentations;to the LAMAVE
Project researchers, especially to Ms. Jessica Labaja, and to their
project head, Dr. Alessandro Ponzo, for their kindness and
willingness to help every time we visit Pintuyan despite their
hectic research schedules; to Pastor Ernesto Felicio, kuya Gerry,
Mr. Virgilio Flores and the whole barangay of Son-ok dos, for being
so accommodating and for providing us motor boats;to Mr. Rey
Verona, for letting us borrow laboratory instruments;to Mr. Joseph
Dominic Palermo, for answering our questions regarding zooplankton
and confirming the zooplankton we identified;to kuya James Ostrea
and ate Kim Ruizo, for the help during our first sampling and
additional information regarding the methods of this study;to Ms.
Sharmaine Ida, for the company, assistance and shared struggles
during the whole study period;to Ms. Retsie Corado, Mr. Daniel
Licayan, Ms. Pearl Joy Angelie Sigua and ate Coleen Alonzo, for the
shared plankton experiences and overnights;to Mr. John dela Cruz
and Mr. John Paul Ada, for the help during the final stages of this
research paper; to Ms. Haide Batula, who has always been there for
me like the phytoplankton for the zooplankton;to my family, who
never stopped believing and prayed for me always; and,most
importantly, to God, for these great people above and all the
blessing He bestowed upon the duration of this study.
ABSTRACT
Sampling stations in the study site off Sogod Bay, Southern
Leyte were established along the feeding grounds of whale shark
(Rhincodon typus). The whale shark season in the area is known to
last from November to July. Water samples and physico-chemical
parameters from three sampling stations were taken and collected
once a month in August and October in year 2013 within the off
whale shark season period, and March 2014 within the whale shark
season. Abundance, composition, and diversity of zooplankton groups
encountered were quantified. Copepods dominated by 66% (Order
Calanoida 26%, copepod nauplius 16%, Order Cyclopoida 14% and Order
Harpacticoida 10%) of the total zooplankton population. October
2013 had the least mean density of 1.9x103 ind./L. August 2014
samples had the least zooplankton diversity of H = 1.58. Samples
obtained during the whale shark season, March 2014, showed the
highest total zooplankton abundance at 7.7x103 ind./L. This also
yielded the highest zooplankton community diversity of H =
2.53.
TABLE OF CONTENTS
PageAcknowledgements...iiiAbstract ........vList of
Tables....viiiList of Figures..........ixIntroduction...1Literature
Review........3Importance of Zooplankton in Marine
Communities..3Marine Zooplankton in Southeast Asia...4Rhincodon
typus and its Feeding Habits..4Rhincodon typus in the
Philippines....6Sogod Bay, Southern Leyte....6Methodology...8Study
Site....8Physico-chemical Analysis..8Collection and Preparation of
Samples...10Zooplankton Identification..11Cell Density
Determination.11Data Analyses..12Results..13Zooplankton Abundance
and Composition.13Quantitative Analysis..13Qualitative
Analysis17Zooplankton Diversity.17Physico-chemical
Parameters......18Discussion....21Zooplankton Abundance off Sogod
Bay, Southern Leyte..21Diversity and Composition of Zooplankton
Groups off Sogod Bay, Southern Leyte.22Zooplankton Abundance and
Diversity per Sampling
Station23Conclusion......................................................................................................24Recommendation.........25References....26Appendix.........29
LIST OF TABLES
Page
Table 1. Zooplankton groups observed off Sogod Bay, Southern
Leyte.14Table 2. Summary of physico-chemical parameters during
August (2013), October (2013) and March (2014) sampling in Sogod
Bay, Southern Leyte, Philippines.20
LIST OF FIGURES
PageFigure 1. Sampling Stations off Sogod Bay, Southern Leyte
from August 2013 to March 2014...9Figure 2. Zooplankton composition
and density in Stations 1, 2 and 3 in the sampling months August
and October 2013, and March 2014 off Sogod Bay, Southern
Leyte......15Figure 3. Mean zooplankton abundance in the months of
August and October 2013, and March 2014 off Sogod Bay, Southern
Leyte ...16Figure 4. Actinotrocha larvae from Family Phoronidae of
Phylum Phoronida in Station 2 during March 2014
sampling....17Figure 5. Zooplankton diversity (H) in Stations 1, 2,
and 3 in the months of August and October 2013, and March 2014 off
Sogod Bay, Southern Leyte..18
ii
INTRODUCTION
Zooplankters are essential in every marine community because of
their richness and number. The most prominent zooplankton, the
copepods, is regarded to be the most abundant multicellular animals
on Earth (Schminke 2007). Zooplankton communities are proven to
have high diversity and thus perform a variety of important
ecosystem functions and roles especially in aquatic food webs. They
are considered to make up the trophic level of primary consumers
which makes them critical to the functioning of ocean food webs
(Richardson 2008).Almost all of zooplankton preys upon the primary
producers, the phytoplankton. They also feed on other zooplankton
groups (e.g. medusae), fish eggs and larvae in their diet. They are
in turn preyed upon by bigger fish larvae and many adult
planktivorous fish. The position of zooplankton in the food web is
thus between primary producers and predators. Zooplankton serves as
a link between bottom-up climate-related control of phytoplankton
and fish and paves the pathway for energy transfer from primary
producers to consumers at higher trophic levels (Lalli and Parsons
1997, Ayon et al. 2008, Richardson 2008). Large animals in the
ocean such as filter-feeding sharks and whale rely solely to feed
on plankton and small fishes (Richardson 2008). The whale shark or
Rhincodon typus is one of three species of large pelagic sharks
that rely on plankton and small nekton as their food source (Colman
1997). Whale sharks have two feeding strategies; passive
sub-surface ram-feeding and active surface feeding (Gudger 1941).
Passive feeding involves opening of the mouth while swimming and
filtering water in its path. Active surface feeding on the other
hand makes use of a suction filter-feeding mechanism that sucks in
and filters water while remaining still (Gudger 1941). These kinds
of feeding behavior make R. typus dependent on densely populated
patches of plankton (Heyman et al. 2001). Whale sharks are
migratory and are known to inhabit tropical and warm temperate
water (Stacey et al. 2008). This includes Philippine waters as site
of whale shark migrations (Barut et al. 2003) . There are reports
of whale shark sightings at Donsol and Bohol Sea (Alava and Cantos
2004) and recently, Sogod Bay, Southern Leyte (Bochove et al.
2007). The sampling stations established in Sogod Bay are feeding
grounds of whale sharks suggested by Dr. Alessandro Ponzo,
president of Physalus, a non-profit organization. Physalus conducts
the LAMAVE (Large Marine Vertebrate) Project in the Philippines
which aims to raise environmental awareness of large marine
vertebrates through scientific research. This research will provide
baseline data of the abundance of zooplankton species that the
Rhincodon typus feed on along its migration path in Sogod Bay,
Southern Leyte. It will also serve to validate the hypothesis that
these areas are feeding grounds of the whale shark, Rhincodon
typus. Consequently, this study has the following objectives:1. To
identify the zooplankton groups present in the study site; and2. To
quantify the abundance and diversity of zooplankton present in the
feeding ground off Sogod Bay, Southern Leyte.
LITERATURE REVIEW
Importance of Zooplankton in Marine Communities
Microscopic animals that are found in bodies of water are known
as zooplankton. They take part in the marine food web and are
essential in the study of marine ecology and diversity. Zooplankton
communities are considered to have high diversity. The most
prominent zooplankton, the copepods, is regarded to be the most
abundant multicellular animals on Earth. Copepods, by possibly
three orders of representatives, are able to outnumber the insects
(Schminke 2007).Restrictions in the swimming capabilities of
zooplankters make these organisms be carried easily by the water
current. Thus, zooplankters are grazed upon and eaten by
planktivorous organisms since they are an easy prey and are usually
found in patches (Nybakken 1982). Zooplankton species acquire
energy in different ways. Different species of zooplankters employs
a variety of carnivory, herbivory, omnivory, and detritivory. With
wide food choices available for these organisms, zooplankton are
among the primary consumers of the marine food webs and are
considered as key organisms, playing an important role in energy
transfer and a link to nutrients from the producers to bigger
organisms such as fishes (Lalli and Parsons 1997, Ayon et al. 2008,
Richardson 2008). In addition, zooplankton such as larvaceans,
copepods, and euphausiids are capable of reprocessing marine snow
and other nutrients eaten into much dense and larger fecal pellets
(Wilson et al. 2013). These nutrient packed pellets sink faster
down the water column, which is exported to be eaten by other
organisms below (Turner 2002). Zooplankton takes part in the
biogeochemical cycling processes especially in the carbon cycle in
the ocean since they expend carbon for their respiration processes
(del Giorgio and Duarte 2002). In a study conducted by
Hernandez-Leon and Ikeda (2005), it was found that more than
one-third of the organic carbon ow in the ocean is contributed by
mesozooplankton through cycling that makes up to a 1732%
respiratory loss of photosynthetic carbon produced in the open
ocean.
Marine Zooplankton in Southeast Asia
Southeast Asia has a high species diversity of macro fauna
because of this regions unique settings. In fact, Southeast Asia is
referred to as the worlds center of marine biodiversity. To prove
this, an estimate of more than 550 species or one fourth of the
total species of pelagic copepods are identified and are known to
inhabit this region. The discoveries and count of zooplankton are
still growing in this region. Twenty-nine planktonic copepods and
16 mero-planktonic or non-planktonic copepods, 4 amphipods, and 2
isopods were described as new to science in recent studies and an
additional of 37 species of mysids were described as new from
Southeast Asia and Japanese waters. Many of these new species are
found in untouched and poorly investigated areas such as estuaries,
benthopelagic zones, coral reefs and marginal basins (Nishida and
Nishikawa 2011).
Rhincodon typus and its Feeding Habits
Rhincodon typus, commonly called the whale shark, is the only
representative of the family Rhincodontidae and the current known
largest extant fish species (Compagno 1984). The whale shark,
together with the Basking Shark (Cetorhinus maximus) and the
Megamouth Shark (Megachasma pelagios), are considered to be the
only filter-feeding shark species relying solely on plankton and
nekton as their food source (Colman 1997). Whale sharks are
distributed along tropical, sub-tropical and a few recorded in warm
temperate waters and are known to be highly migratory but returns
to same sites annually (Compagno 1984, Colman 1997). Whale sharks
are usually harmless to humans even though they are enormous in
size. The largest whale shark, found in Taiwan, reached a length of
20 meters and weighed 34 tons (Chen and Phipps 2002). Since whale
sharks are filter-feeders, their food preferences include a variety
of almost all suspended organisms in the ocean such as zooplankton,
nekton, and several small fish (Gudger 1941, Compagno 1984, Colman
1997).Whale sharks are usually found individually but sometimes
they aggregate. In Gladden Spit, Belize, about 25 whale sharks are
found aggregating mainly feeding on fresh spawn of cubera, Lutjanus
cyanopterus, and dog snappers Lutjanus jocu (Heyman et al. 2001).
Recently, a newly discovered aggregation site of whale sharks was
found at Al Shaheen oil field, which is 90 kilometers off the coast
of Qatar in the Arabian Gulf. About 100 individuals were estimated
within an area of 1 km2 feeding on surface zooplankton, consisting
primarily of mackerel tuna (Euthynnus affinis) eggs (Robinson et
al. 2013). The whale sharks are observed to exhibit two types of
feeding behavior: passive sub-surface ram-feeding and active
surface feeding. Passive feeding involves opening of the mouth
while slowly swimming and filtering water in its path. Active
surface feeding on the other hand makes use of a suction
filter-feeding mechanism. An active feeder sucks in and filters
water while remaining still either horizontally or vertically
(Gudger 1941).
Rhincodon typus in the Philippines
In a study conducted by Eckert et al. (2002), using satellite
telemetry, the movements and distances travelled by individual
whale sharks starting from the greater Sulu Sea region were
recorded. The rate of travel of the whale sharks observed averages
24 km/day, a proof that sharks were highly mobile and did not seem
to remain in any particular area. The Philippines is a tropical
country making it a part of the whale sharks migration route (Barut
et al. 2003). Whale shark is commonly called butanding in the
Philippines. Whale shark sightings occurring singly or in groups
nearshore and offshore are recorded in many areas of the
Philippines (Barut et al. 2003). Fishery records show abundance of
whale shark particularly around the Bohol and Sulu Seas and
southeastern Mindanao (Alava and Cantos 2004). Other places in the
Philippines where seasonal aggregation of whale sharks can be
observed include Donsol, Sorsogon, Honda Bay, Palawan, Zambales
coasts (Alava and Cantos 2004), and Sogod Bay, Southern Leyte
(Bochove et al. 2007).
Sogod Bay, Southern Leyte
Sogod Bay can be found in the southernmost part of Southern
Leyte, one of the six provinces of Eastern Visayas. Some of the
coral reefs in the Philippines that remain to be the least
disturbed and least researched are found in the waters of Southern
Leyte. A large body of water in Southern Leyte, which is the Sogod
Bay, serves as an important fishing spot for fishermen living by
the coastlines of the bay. Sogod Bay is known to host a variety of
reef fish and other commercially marketed fish such as tuna, flying
fish, herrings, anchovies, shellfish, and mackerel (Bochove et al.
2007). The abundance of fish also means that the bay is a major
breeding ground of fishes where they spawn and reproduce making it
an attractive food source for large opportunistic forager organisms
such as pilot whales, melon-headed whales, dolphins, and whale
sharks (Bochove et al. 2007). According to Mr. Ernesto Felicio
(pers. comm.), whale sharks were often found drifting along the
Pintuyan point and Son-ok point as long as he can remember.
METHODOLOGY
Study Site
Three sampling stations were established along the southern part
of Sogod Bay, Southern Leyte. Sampling Station 1 is situated near
the tip of Pintuyan (N 09 54 56.9, E 125 15 10.9), Station 2 is
situated near Bennet Port of San Ricardo (N 09 54 53.69, E 125 17
32.7), and Station 3 is situated in deeper waters (N 9 54 29.8, E
125 17 18.1).
Physico-chemical Analysis
Physico-chemical parameters of the waters in each sampling
station were taken and recorded. These include current velocity,
depth, light intensity, temperature, salinity, dissolved oxygen,
and pH. Velocity of the current was assessed with the use of a
fabricated drogue. The drogue was allowed to drift freely in the
direction of the current until it reached one meter. The time it
took to reach one meter was recorded and the direction of the
current was estimated using a compass. Current was calculated using
the following formula:
Depth was measured using a calibrated rope. Light intensity was
measured with the use of EXTECH light meter. Temperature was
measured with the use of a centigrade field thermometer. Salinity
was examined using a handheld Attago refractometer. Dissolved
Oxygen, and the pH of the water was measured using a EUTECH
multiparameter.
Figure 1. Sampling Stations off Sogod Bay, Southern Leyte from
August 2013 to March 2014.
Collection and Preparation of Samples
Water samples at each station were collected once every sampling
period in the months of August and October of year 2013 and March
2014. Qualitative AnalysisA conical plankton net extending up to
one meter in length with a 30 cm diameter and 20 m mesh size was
used for obtaining water samples. The plankton net was lowered one
meter below the surface and then towed vertically. Water samples
collected were dispensed to a 100 mL pre-labeled plastic bottle
then, ten milliliters of formalin was added for preservation. Water
samples were collected twice per station.
Quantitative AnalysisA 2.2L capacity WILDCO vertical sampler was
lowered one meter below water surface at each station followed by a
messenger that triggered the trapping mechanism of the sampler,
sealing the water. Water collected was transferred to a pre-labeled
one liter plastic bottle. Ten milliliters of formalin was added for
fixation and preservation. Water samples were collected twice per
station.
Preparation of SamplesThe preserved one liter samples were
stored undisturbed for 24 hours which allowed settlement of the
preserved and suspended plankton. After settling, a capillary tube
was placed carefully in the bottle which sucked out 800mL of
supernatant. The remaining 200mL of the sample was transferred into
a 250mL graduated cylinder and was stored again for 24 hours
undisturbed. After settling, 150mL of supernatant was dispensed
using the same suction technique. A concentrated final volume of
approximately 50mL of the sample was acquired and transferred into
a 50mL amber bottle.
Zooplankton Identification
One-milliliter of the 250mL sample for qualitative analysis was
placed on a glass slide. It is then viewed under a light compound
microscope with 150x magnification. Zooplankton samples were
identified based on their structure and morphology using the
taxonomic keys of Yamaji (1984) and Larink and Westheide (2006).
Identification was conducted up to family or order level.
Photomicrograph softcopies of the zooplankton identified was
verified by Mr. Joseph Dominic Palermo from Marine Science
Institute, University of the Philippines Diliman.
Cell Density Determination
One-milliliter of the 50mL concentrated sample was obtained for
cell density determination. The storage bottle was shaken first to
even out the suspended zooplankton in the sample then
one-milliliter of aliquot was drawn out from the bottle. The
aliquot was dispensed on a Sedgwick-Rafter counting chamber and
then viewed under a light compound microscope. At least 300 cells
were counted in the sample. Cell density was determined using the
following formula:
Data Analyses
Diversity was estimated using Shannon-Wiener index:
Where:H = the Shannon diversity indexPi = fraction of the entire
population made up of species iS = numbers of species encountered =
sum from species 1 to species
RESULTS
Zooplankton Abundance and Composition
Quantitative Analysis
There were nineteen zooplankton groups encountered in the study.
Copepod nauplii were observed but grouped as one since each species
from different orders were morphologically indiscernible from one
another under an ordinary light microscope. All zooplankton groups
were observed in the month of March 2014. Families Phyllodocidae
and Veneridae were absent in the month of October 2013 while
families Atlantidae and Limacinidae were absent in the month of
August 2013. (See Table 1)Copepod nauplius dominated the August and
October 2013 sampling periods with densities of 5.8x102 ind./L and
4.7x102ind./L respectively. By March 2014, all stations were
dominated by family Calanidae (1.1x103 ind./L) copepods. (See
figure 2) The highest total density (7.9x103 ind./L) was observed
in Station 2 during March 2014 sampling while the lowest (1.3x103
ind./L) was observed in October 2013 sampling (See figure 2).
Accounting for all stations and comparing each month, the highest
mean total density was 7.7x103 ind./L in the month of March 2014
and the lowest was 1.9x103 ind./L in the month of October 2013.
(See figure 3)1
11
Table 1. Zooplankton groups observed off Sogod Bay, Southern
Leyte. Orders Calanoida, Cyclopoida, Harpacticoida, and
Poecilostomatoida are classified as copepods. Teleost eggs and
ophiuroid larvae were not identified to family level due to the
lack of morphological features
OrderCalanoidaCyclopoidaHarpacticoidaPoecilostomatoidaSessiliaOligotrichida
FamilyCalanidaeOithonidaeEctinosomatidaeOncaeidaeBalanidaeRhabdonellidae
ParacalanidaeCorycaeidaeTintinnidae
Codonellidae
PhylumMolluscaAnnelidaChordataEchinodermata
FamilyAtlantidaePhyllodocidaeOikopleuridaeOphiuroidea
(class)
LimacinidaeSabillaridaeTeleost Eggs (not family)
Veneridae
Figure 2. Zooplankton composition and density in Stations 1, 2
and 3 in the sampling months August and October 2013, and March
2014 off Sogod Bay, Southern Leyte. The colored section of the bars
refer to copepod zooplankton groups and the shades of grey refer to
non-copepod zooplankton groups Figure 3. Mean zooplankton abundance
in the months of August and October 2013, and March 2014 off Sogod
Bay, Southern Leyte. The colored section of the bars refer to
copepod zooplankton groups and the shades of grey refer to non-
copepod zooplankton groups
Figure 4. Actinotrocha larvae from Family Phoronidae of Phylum
Phoronida in Station 2 during March 2014 sampling.
Qualitative Analysis
The same zooplankton groups observed in quantitative analysis
were also observed in the qualitative analysis. However, an
additional zooplankton group (Actinotrocha larvae from Family
Phoronidae of Phylum Phoronida) was observed in the sample from
Station 2 in the March 2014 sampling.
Zooplankton Diversity
Diversity values for the three stations during the months of
August and October 2013 and March 2014 is shown in figure 5.
Station 2 during the March 2014 sampling has the highest recorded
diversity of H = 2.56. On the other hand, Station 1 was the least
diverse station in October 2013 sampling with a diversity value of
H = 1.44.
Figure 5. Zooplankton diversity (H) in Stations 1, 2, and 3 in
the months of August and October 2013, and March 2014 off Sogod
Bay, Southern Leyte
Physico-chemical Parameters
Values of physico-chemical parameters determined per station are
summarized in Table 1. Depth ranged from 4.5 to 10 m in Stations 1
and 2. The deepest sampling station was Station 3 with depths
reaching approximately 15 m 27 m. Light intensity values range from
1.77103 Fc to 7.51.103 Fc. Temperature ranged from 28-30.4 C with
the highest temperature, 30.4C, recorded in Station 2 during March
2014 sampling and the lowest temperature, 28 C, recorded Station 1
during the month of October 2013. Values for pH measured varied
from 7.9 - 8.53. Salinity was highest during the month of March
with the highest value of 38 ppt recorded in Station 3 while values
for the months of August 2013 and October 2013 ranged from 29 - 30.
However, dissolved oxygen during the month of August in Stations 1
and 2 were recorded with DO values of 8.01 mg/L and 7.55 mg/L,
respectively. DO was not measured for the sampling months of
October and March.
Table 2. Summary of physico-chemical parameters during August
(2013), October (2013) and March (2014) sampling in Sogod Bay,
Southern Leyte, Philippines. (N.d. = no data)
Depth (m)Light Intensity (Fc)Temperature
(C)Salinity(ppt)pHDissolved Oxygen (mg/L)
August6.53.93103 7.51.10329 30.330 30.38.02 8.037.55 8.01
October7- ~27 m1.77103 5.310328 3029 357.9 - 8.02N.d.
March 10-202.53103 6.4610329 30.432 388.23 8.53N.d.
DISCUSSION
Zooplankton Abundance off Sogod Bay, Southern Leyte
Copepods, according to a review by (Kiorboe 2011) are successful
due to their predator escaping and prey capturing capabilities.
Copepods are also efficient in locating mate in the dilute
community they thrive in (Kiorboe 2011). High abundance of copepod
nauplii throughout the whole sampling period can be attributed to
the high productivity of copepod species in the study site. As
stated earlier, copepod nauplii and other small zooplankton are
mostly preyed upon by bigger omnivorous and carnivorous
zooplankton. Hence, contribution of copepod nauplii in the marine
community is ecologically significant. Figure 2 testifies the large
contribution of copepod nauplii in the zooplankton population in
all sampling periods dominating the sampling months of August and
October 2013. In proportion, the contribution of copepod nauplii in
the population decreased during March 2014, showed in Figure 2, due
to the increased number of possible planktonic predators such as
larger zooplankters.Figure 3 shows that the month of October 2013
had the least zooplankton abundance and in contrary March 2014 had
the greatest, up to three times more than October 2013. A
contemporary study conducted by Ida (2014) off Sogod Bay shows the
least and the greatest value of phytoplankton abundance and
diversity in the same months of October 2013 and March 2014
respectively. Zooplankton depend primarily on phytoplankton as food
source, the occurrence of abundant phytoplankton species will
therefore increase zooplankton abundance. As mentioned earlier, the
month of March is included in the duration of whale shark season
off Sogod Bay from November to July. Increased zooplankton grazing
on phytoplankton might be a factor for the whale shark migration in
the mentioned bay. According to (Martin 2007), like the baleen
whale and some procellariid birds, the whale shark might also take
the chemical released by phytoplankton when they are grazed upon by
zooplankton as a foraging cue.Also, a notable observance is the
significant inflation in harpacticoid abundance (see Figure 2). The
large increase in number of harpacticoid species compared to other
zooplankton in the month of March 2014 can be attributed to the
warm season during this month. Compared to August and October 2013
as shown in Table 1, the month of March 2014 has the highest
recorded temperature, salinity and light intensity. According to
(Uye et al. 2002), most harpacticoid species tend to reproduce more
during warm season because the duration time from egg laying to
adulthood best depends on higher temperature.
Diversity and Composition of Zooplankton Groups off Sogod Bay,
Southern Leyte
The increased diversity in the month of March 2014 can be
attributed to the increase in zooplankton abundance and
composition. Additional zooplankton groups were encountered in
samples taken during the same month. These additional groups
include the free swimming larvae of Family Phoronidae Actinotroch,
and Class Ophiuroidea Pluteus. Adult forms of phoronids or horshoe
worms and ophiuroids or brittle stars are basically bottom dwelling
organisms. Also an increase in teleost egg density from 13 ind./L
during October 2013 to 100 ind./L during March 2014 was observed.
Though these zooplankton groups are not plentiful enough to be
considered as significant contributors to the total zooplankton
population in the three stations, occurrence of more meroplanktonic
forms and increase in their diversity in the month of March may
suggest that this presence of a number of prey resources are part
of the whale sharks prey diet despite the fact that majority of
what they consume are holoplanktonic zooplankton (e.g. copepods)
(Nelson and Eckert 2007). However, krills or euphausiids, were not
encountered in any of the stations in the study site during the
three sampling events. Krills are also one of the preferred food of
the whale shark. In some parts of Bohol Sea, Philippines, locals
use krills and mysis shrimp commonly called as alamang to hand feed
and lure whale sharks (Alava et al. 1997).
Zooplankton Abundance and Diversity per Sampling Station
In contrast to the other sampling stations, Station 2 was the
nearest station to the Bennet Port where there is better mixing of
nutrients in the water. Nearby residential structures are also
observed which can be sources of additional nutrients to run-offs.
The same station was also observed to have the most abundant and
diverse zooplankton composition and phytoplankton (Ida 2014). This
suggests that key nutrients for some zooplankton are accessible in
Station 2 but are either inaccessible or absent in Stations 1 and
3. For instance, the actinotroch larva was only observed in Station
2 during the March 2014 sampling because dinoflagellates were part
of the larvas diet (Strathmann and Bone 1997). A report by Bochove
et al. (2007) and a study by Labaja et al. (2013) account more
sightings of whale shark near Station 2 which can be attributed to
its zooplankton abundance.
CONCLUSION
A total of 19 zooplankton groups were identified. The study site
were dominated by Copepods (66%) followed by Oligotrichida (15%)
and then Polychaetes (11%). High copepod nauplii abundance (16%)
can be attributed to the high productivity of copepods. March 2014,
the sampling event during the whale shark season, yielded the
highest mean abundance (7.7x103 ind./L) of zooplankton. And October
2013, during the off peak season, had the least (1.9x103 ind./L)
zooplankton mean abundance. March 2014 also was the most diverse (H
= 2.53) zooplankton community compared to the first two sampling
events.
RECOMMENDATION
More sampling stations including the non-feeding grounds of
whale is highly recommended for comparative data. Additional depths
for each station and longer sampling duration are also essential to
sample more zooplankton groups. Identification up to genus or
species level is also recommended.
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APPENDIX
Zooplankton Identified
Order Calanoida
Family Calanidae Family Paracalanidae
Order CyclopoidaFamily Corycaeidae Family Oithonidae
Order HarpacticoidaOrder Poecilostomatoida Family
Ectinosomatidae Family Oncaeidae
Copepod Nauplius
Order Sessilia
Family Balanidae Nauplius
Order OligotrichidaFamily RhabdonellidaFamily Tintinnidae
Family Codonellidae
Phylum MolluscaClass GastropodaFamily AtlantidaeFamily
Limacinidae
Class Bivalvia
Family VeneridaePhylum TunicataClass Appendicularia
Family OikopleuridaePhylum AnnelidaClass Polychaeta Family
SabellaridaeFamily Phyllodocidae
Phylum EchinodermataClass Ophiuroidea Pluteus Larvae
Teleost Eggs
