Program     The geochemical and biological study of corals       Poster Diversity of coral-associated Symbiodinium in 15 reef coral species and its potential adaptive strategy to thermal stress in the tropical South China Sea P-G3-13-S Zhenjun Qin* , Coral Reef Research Center of China, Guangxi University, Nanning 530004, China; Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China; School of Marine Sciences, Guangxi University, Nanning 530004, China Kefu Yu*, Coral Reef Research Center of China, Guangxi University, Nanning 530004, China; Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China; School of Marine Sciences, Guangxi University, Nanning 530004, China Yinghui Wang, Coral Reef Research Center of China, Guangxi University, Nanning 530004, China; Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China; School of Marine Sciences, Guangxi University, Nanning 530004, China Biao Chen, Coral Reef Research Center of China, Guangxi University, Nanning 530004, China; Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China; School of Marine Sciences, Guangxi University, Nanning 530004, China Jiayuan Liang, Coral Reef Research Center of China, Guangxi University, Nanning 530004, China; Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China; School of Marine Sciences, Guangxi University, Nanning 530004, China Presenter Email: qzj_gxu@163.com It is well known that different coral species have different tolerances to thermal stress and coral-associated Symbiodinium play an important role in the coral-algal holobiont. However, the relationship between coral-associated Symbiodinium subclade and its density, and coral adaptive strategy to thermal stress are currently not well understood. In this study, we had characterized the Symbiodinium of 15 species of scleractinian corals at Xinyi Reef in the South China Sea, using amplicon sequencing and analysis of internal transcribed spacer 2 (ITS2) for Symbiodinium subclade and using hemocytometer for Symbiodinium denisty. A total of 1,816,596 high-quality sequence reads representing 188 distinct ITS2 sequences were generated and analyzed. 27 ITS2 sequences were present at ≥ 5% abundance in at least one sample, demonstrating the disparity between the total number of ITS2 sequences recovered and their relative proportion. The results showed that all the Symbiodinium denisties of corals were generally in a relatively low density level in this tropical area, but were still followed the regular that massive corals > plating corals > branching corals. High SST resulted in lower levels of Symbiodinium density for all corals. Moreover, the results of Symbiodinium subclade indicated that the composition of the Symbiodinium subclade was mainly determined by the coral host. Carefully analyzing, we found that Porites lutea and Montipora efflorescens associated with the dominated Symbiodinium subclade C15 and Pocillopora verrucosa associated with the dominated Symbiodinium of clade D1 and D1a. They were more resilient to thermal stress than other coral species. This may be well explained that why Porites and Pocillopora are dominated corals in the tropical area of the South China Sea. In contrast, Acropora humilis, Merulina ampliata and the Faviidae (contained five species) associated with the dominated Symbiodinium of C3u and Cspc, which were more conducive to photosynthesis but were sensitive to bleaching. Particularly, the dominated Symbiodinium subclade of the solitary Fungia fungites was C27 unlike all other colonial corals. It indicated that different coral species had different adaptation strategies to thermal stress, and adaptability mainly depended on the Symbiodinium density and Symbiodinium subclade in the tropical sea.

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