surface zooplankton

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

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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

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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 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

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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.

REFERENCES

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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