surface zooplankton sogod bay
TRANSCRIPT
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Surface Zooplankton Community Composition in Whale shark
(Rhincodon typus) Feeding Grounds Off Sogod Bay, Southern Leyteduring August 2013 to March 2014
by
PAUL MATTHEW L. MUNCADA
A research paper submitted to the
Division of Natural Sciences and Mathematics
University of the Philippines Visayas
Tacloban College, Tacloban City
As partial fulfillment of the requirements
for the Degree of
B.S. BIOLOGY
May 2014
Permission is given for the following people to have access to this research:
Available to the general public Yes
Available only after consultation with author/adviser No
Available only for those bound by confidentiality agreement No
Students signature:
Signatur e of Research Adviser :
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This is to certify that this research paper, entitled: Surface Zooplankton
Community Composition in Whale shark (Rhincodon typus) Feeding GroundsOff 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-DEJETO
Research 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. CAPON
DNSM Chair
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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;
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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.
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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.
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TABLE OF CONTENTS
Page
Acknowledgements... iii
Abstract ........ v
List of Tables.... viii
List of Figures.......... ix
Introduction... 1
Literature Review........ 3
Importance of Zooplankton in Marine Communities.. 3
Marine Zooplankton in Southeast Asia... 4
Rhincodon typusand its Feeding Habits.. 4
Rhincodon typusin the Philippines.... 6
Sogod Bay, Southern Leyte.... 6
Methodology... 8
Study Site.... 8
Physico-chemical Analysis.. 8
Collection and Preparation of Samples... 10
Zooplankton Identification.. 11
Cell Density Determination. 11
Data Analyses.. 12
Results.. 13
Zooplankton Abundance and Composition. 13
Quantitative Analysis.. 13
Qualitative Analysis 17
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Zooplankton Diversity. 17
Physico-chemical Parameters...... 18
Discussion.... 21
Zooplankton Abundance off Sogod Bay, Southern Leyte.. 21
Diversity and Composition of Zooplankton Groups off
Sogod Bay, Southern Leyte. 22
Zooplankton Abundance and Diversity per Sampling Station 23
Conclusion...................................................................................................... 24
Recommendation......... 25
References.... 26
Appendix......... 29
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LIST OF TABLES
Page
Table 1. Zooplankton groups observed off Sogod Bay, Southern Leyte. 14
Table 2. Summary of physico-chemical parameters during August (2013),
October (2013) and March (2014) sampling in Sogod Bay,
Southern Leyte, Philippines. 20
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LIST OF FIGURES
PageFigure 1. Sampling Stations off Sogod Bay, Southern Leyte from
August 2013 to March 2014... 9
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...... 15
Figure 3. Mean zooplankton abundance in the months of August and October
2013, and March 2014 off Sogod Bay, Southern Leyte ... 16
Figure 4. Actinotrocha larvae from Family Phoronidae of Phylum Phoronida
in Station 2 during March 2014 sampling.... 17
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.. 18
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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 typusis 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
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mechanism that sucks in and filters water while remaining still (Gudger 1941). These
kinds of feeding behavior makeR. 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; and
2.
To quantify the abundance and diversity of zooplankton present in
the feeding ground off Sogod Bay, Southern Leyte.
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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).
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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 flow 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
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(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 km2feeding
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.
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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
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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.
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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().
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
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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. Red dots indicate the sampling stations
Station 1
Station 2Station 3
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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 Analysis
A 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
collected was 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 Analysis
A 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 Samples
The 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
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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:
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Data Analyses
Diversity was estimated using Shannon-Wiener index:
Where:
H = the Shannon diversity index
Pi = fraction of the entire population madeup of species i
S = numbers of species encountered
= sum from species 1 to species
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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)
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Table 1. Zooplankton groups observed off Sogod Bay, Southern Leyte. Orders Calanoida, Cyclopoida, Harpacticoida, andPoecilostomatoida are classified as copepods. Teleost eggs and ophiuroid larvae were not identified to family level due to
the lack of morphological features
Order Calanoida Cyclopoida Harpacticoida Poecilostomatoida Sessilia Oligotrichida
Family Calanidae Oithonidae Ectinosomatidae Oncaeidae Balanidae Rhabdonellidae
Paracalanidae Corycaeidae Tintinnidae
Codonellidae
Phylum Mollusca Annelida Chordata Echinodermata
Family Atlantidae Phyllodocidae Oikopleuridae Ophiuroidea (class)
Limacinidae Sabillaridae Teleost Eggs (not family)
Veneridae
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Figure 2. Zooplankton composition and density in Stations 1, 2 and 3 in the samplingmonths August and October 2013, and March 2014 off Sogod Bay, Southern
Leyte. The colored section of the bars refer to copepod zooplankton groupsand the shades of grey refer to non-copepod zooplankton groups
0 1 2 3 4 5 6 7 8
Station 1
Station 2
August
0 1 2 3 4 5 6 7 8
Station 1
Station 2
Station 3
October
0 1 2 3 4 5 6 7 8
Station 1
Station 2
Station3
density (x103ind./L)
March
Copepod Nauplius Calanidae Paracalanidae Oithonidae
Corycaeidae Ectinosomatidae Oncaeidae Balanidae
Rhabdonellidae Codonellidae Tintinnidae Ophiuroidea
Atlantidae Limacinidae Veneridae Phyllodocidae
Sabellaridae Oikopleuridae Teleost Egg
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Figure 3. Mean zooplankton abundance in the months of August and October 2013, andMarch 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
0
1
2
3
4
5
6
7
8
August October March
density
(x103ind.
/L)
Sampling Months
Teleost Egg
Oikopleuridae
Sabellaridae
Phyllodocidae
Veneridae
Limacinidae
Atlantidae
Ophiuroidea
Tintinnidae
Codonellidae
Rhabdonellidae
Balanidae
Oncaeidae
Ectinosomatidae
Corycaeidae
Oithonidae
Paracalanidae
Calanidae
Copepod Nauplius
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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.
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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 7.51.103Fc. 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
1.47
1.70
1.44
1.77
1.66
2.49
2.56
2.54
0 0.5 1 1.5 2 2.5 3
Station 1
Station 2
Station 1
Station 2
Station 3
Station 1
Station 2
Station 3
Shannon-Wiener Diversity Index (H')
March 2014
October 2013
August 2013
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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.
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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)
August 6.5 3.931037.51.10
3 2930.3 3030.3 8.028.03 7.558.01
October 7- ~27 m 1.771035.310
3 2830 2935 7.9 - 8.02 N.d.
March 10-20 2.531036.4610
3 2930.4 3238 8.238.53 N.d.
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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.
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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
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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.
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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 (1.9x103ind./L) zooplankton
mean abundance. March 2014 also was the most diverse (H= 2.53) zooplankton
community compared to the first two sampling events.
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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 Cyclopoida
Family Corycaeidae Family Oithonidae
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Order Oligotrichida
Family Rhabdonellida Family Tintinnidae
Family Codonellidae
Phylum Mollusca
Class Gastropoda
Family Atlantidae Family Limacinidae
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Class Bivalvia
Family Veneridae
Phylum Tunicata
Class Appendicularia
Family Oikopleuridae
Phylum Annelida
Class Polychaeta
Family Sabellaridae Family Phyllodocidae
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Phylum Echinodermata
Class Ophiuroidea Pluteus Larvae
Teleost Eggs