DIVERSITY AND ABUNDANCE OF ZOOPLANKTON IN CORAL COMMUNITIES AT KO SAK, CHONBURI PROVINCE FOLLOWING THE 2010 CORAL BLEACHING EVENT

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1 I_I DIVERSITY AND ABUNDANCE OF ZOOPLANKTON IN CORAL COMMUNITIES AT KO SAK, CHONBURI PROVINCE FOLLOWING THE 2010 CORAL BLEACHING EVENT Arporn Sompaonoi,* Sittiporn Pengsakun, Wanlaya Klinthong, Makamas Sutthacheep, Thamasak Yeemin Marine Biodiversity Research Group, Department of Biology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, THAILAND * apple_krung@hotmail.com Abstract: Studies on zooplankton in coral communities are important and can contribute to make potential for prediction of fluctuations in recruitment for commercially exploited marine species. This study was conducted to examine the diversity and abundance of zooplankton in coral communities at Ko Sak, Chonburi Province before, during and after the 2010 coral bleaching event. The survey in March 2010, before the coral bleaching event, showed that live coral coverage was 54.3% but it dropped to 29% in October 2010, following the bleaching event. There were 30 groups of zooplankton with the total density 64,897.4 individuals.m -3 from the sampling in March Twenty-five groups of zooplankton with the total density 128,727.5 individuals.m -3 were recorded during the coral bleaching event in June The zooplankton sampling following the coral bleaching event in October 2010 showed 18 groups of zooplankton with the total density 72,152.9 individuals.m -3. The present study provides important data of temporal variation of zooplankton communities on the coral assemblages at Ko Sak, including larvae of economically important species. Introduction: Knowledge on the relationships between environmental factors and the structure of zooplankton community is a crucial challenge for marine ecosystem studies. It may help determine the origin of spatial and temporal variations in food availability for economically important species, and thus identify the habitats and water masses in which they find the most suitable. 1,2 Moreover, it may contribute to make potential for prediction of fluctuations in recruitment for commercially exploited marine species. 3 In tropical seas, these aspects have rarely been examined, and the small-scale spatial and temporal patterns in zooplankton composition of coral communities remain little known. 4,5 The anomaly of high seawater temperature in June-September 2010 led to impacts on coral communities in the inner Gulf of Thailand. The most susceptible corals to the bleaching event were Montipora tuberculosa, Acropora spp., Pocillopora damicornis and Porites spp. The present study was therefore conducted in order to examine the diversity and abundance of zooplankton in coral communities at Ko Sak, Chonburi Province before, during and after the 2010 coral bleaching event. Methodology: The study site was located at Ko Sak (12 59' 45.64"N, ' 25.77"E) in the inner Gulf of Thailand (Figure 1). The first survey was done in March 2010 (before the coral bleaching event). The survey during the bleaching event was conducted in June We monitored again after the bleaching event in October In each study period, we examined coral conditions and zooplankton communities. The coral conditions were observed in five permanent belt transects of 10x1 m 2 for each. Coverage of living corals, dead corals and other benthic components was quantitatively estimated. Zooplankton was collected with a standard 120 µm mesh plankton net with mouth diameter of 30 cm by vertical hauls (7 m. deep) in a day time. The planktons were fixed in 4 % seawater-formalin. Zooplankton was sorted, identified to the lowest taxonomic level possible,

2 I_I and counted under a dissecting microscope in the laboratory. All zooplankton densities were reported as number of individuals per cubic meter (ind.m -3 ) Two-way ANOVA was used to test the influence of major groups of zooplankton and sampling periods on density of zooplankton. Where significant differences were established, Scheffe s F test was employed to determine which groups differed. Figure 1. Map of the study site at Ko Sak, Chonburi Province, the inner Gulf of Thailand Results, Discussion and Conclusion: The survey in March 2010, before the coral bleaching event, revealed that live coral coverage was 54.3%. The corals showed bleaching signs about 50% during the survey in June The live coral coverage dropped to 29% in October 2010, following the bleaching event.

3 I_I Coverage (%) Live coral Dead coral Rock Sand Rubble Mar-10 Jun-10 Oct-10 Figure 2. Coverage of live and dead corals at Ko Sak during March-October 2010 The zooplankton sampling in March 2010 showed that there were 30 groups of zooplankton with the total density 64,897.4 individuals.m -3. We found 25 groups of zooplankton with the total density 128,727.5 individuals.m -3 during the coral bleaching event in June Six groups of zooplankton were not recorded during the bleaching event, i.e. Siphonophora, Isopoda, Amphipoda, shrimp larvae, crab zoea and fish eggs. However 17 groups of zooplankton had higher density, compared with before the bleaching event. The zooplankton sampling following the coral bleaching event in October 2010 revealed that there were 18 groups with the total density 72,152.9 individuals.m -3. Thirteen groups of zooplankton were not found after the bleaching event, i.e. Nematoda, Platyhelminthes, Rotifera, Cladocera, Mysidacea, Isopoda, Amphipoda, shrimp larvae, crab zoea, bipinnaria larvae, ophiopluteus larvae, fish larvae and fish eggs but 10 groups of zooplankton had higher density, compared with before the bleaching event (Figures 3, 4 and 5) Density (Individuals/m 3 ) Mar-2010 Jun-2010 Oct-2010 Figure 3. The total densities of zooplankton (Means±SE) at Ko Sak during March-October 2010

4 I_I Density (Individuals/m 3 ) Mar-2010 Jun-2010 Oct Figure 4. Diversity and density of zooplankton (Means±SE) at Ko Sak during March-October 2010 Caustacea nauplii Calanoid copepoda Lavacea Figure 5. Some dominant groups of zooplankton at Ko Sak The result of two-way ANOVA and Scheffe s F test showed that the densities of four major groups of zooplankton varied significantly among the three sampling periods (Table 1, ANOVA, P<0.05)

5 I_I Table 1. Result of two-way ANOVA and Scheffe s F test examining the effect of time and species on zooplankton density Source of variation df Mean square F p Two-way ANOVA test Time <0.001* Species <0.001* Time x Species <0.001* residual Total 36 Scheffe s test Effect of time Mar 2010 vs Jun 2010 <0.001* Mar 2010 vs Oct 2010 <0.001* Jun 2010 vs Oct 2010 <0.001* Effect of species Caustacaen nauplii vs Lavacean <0.001* Caustacaen nauplii vs Calanoid <0.001* copepod Caustacaen nauplii vs Cyclopoid <0.001* copepod Lavacean vs Calanoid copepod <0.001* Lavacean vs Cyclopoid copepod <0.001* Calanoid copepod vs Cyclopoid <0.001* copepod *Significant difference (P<0.05), df: Degree of freedom The present study provides important data of temporal variation of zooplankton communities on the coral assemblages at Ko Sak, including larvae of commercially exploited marine species. The study in a coral reef lagoon of New Caledonia, Southwest Pacific showed that the total zooplankton density also progressively increased along the sampling period and the composition of assemblages differed between the lagoon and the bays. Wind speed, surface temperature, chlorophyll a and POM were proposed to explain these variations. 5 Further studies are required to examine the relationships between environmental factors and zooplankton communities in coral reef ecosystems. Moreover, it is necessary to develop appropriate equipments and methods for zooplankton sampling in coral reef areas. References: 1. Fortier L, Levasseur ME, Drolet R, Therriault JC: Mar Ecol Prog Ser 1992; 85: Carleton JH, Hamner WM: Mar Ecol Prog Ser 2007; 336: Castonguay M, Plourde S, Robert D, Runge JA, Fortier L: Can J Fish Aquat Sci: 2008; 65: Alldredge A L, King JM: Coral Reefs 2009; 28: Carassou L, Le Borgne R, Rolland E, Ponton D: Mar Poll Bull 2010; 61:

6 I_I Acknowledgements: This research was funded by a budget for research promotion from the Thai Government to Ramkhamhaeng University in the fiscal years B.E We thank staff of Marine Biodiversity Research Group, Faculty of Science, Ramkhamhaeng University for their assistant. Keywords: zooplankton, coral community, bleaching, diversity, Gulf of Thailand