Symbiont communities and host genetic structure of the brain coral Platygyra verweyi, at the outlet of a nuclear power plant and adjacent areas SHASHANK KESHAVMURTHY,* CHIA-MIN HSU,*† CHAO-YANG KUO,* PEI-JIE MENG,‡§, JIH-TERNG WANG – and CHAOLUN A. CHEN,*,†,** *Biodiversity Research Center, Academia Sinica, Nangang, Taipei 115, Taiwan, †Institute of Oceanography, National Taiwan University, Taipei 106, Taiwan, ‡National Museum of Marine Biology ⁄ Aquarium, Checheng, Pingtung 944, Taiwan, §Institute of Marine Biodiversity and Evolution, National Dong Hwa University, Checheng, Pingtung 944, Taiwan, –Institute of Biotechnology, Tajen University of Science and Technology, Pingtung 907, Taiwan, **Taiwan International Graduate Program (TIGP)-Biodiversity, Academia Sinica, Nangang, Taipei 115, Taiwan Abstract In the context of rising seawater temperatures associated with climate change, the issue of whether coral holobionts deal with this challenge by shuffling their associations with stress- and ⁄ or heat-tolerant Symbiodinium, by generating heat-resistant host genotypes, or both is important for coral survival. In this study, the composition of communities of the endosymbiont Symbiodinium and the population genetics of the coral host Platygyra verweyi were examined in a reef impacted by hot-water discharged from the outlet of a nuclear power plant in operation in Kenting, Southern Taiwan since 1984. The water at this site is 2.0–3.0 °C warmer than adjacent reefs in summer, which have an average seawater temperature of 29.0 °C. The data were compared with those for the same species at other sites within 12 km of the outlet site. Platygyra verwyei was associated with one or both of Symbiodinium types C3 (heat sensitive) and D1a (heat tolerant) at all sites with the latter being the dominant at the nuclear power plant outlet. The proportion of C3 in populations increased gradually with increasing distance from the hot-water discharge. Genetic analysis of the Platygyra verweyi host using mitochondrial and nuclear markers showed no genetic differentiation among sites. Changes in the composition of Symbiodinium types associated with P. verweyi among closely located sites in Kenting suggested that this coral might have acclimatized to the constant thermal stress by selective association with heat-tolerant Symbiodinium types, whereas the role of the host in adaptation was inconclusive. Keywords: acclimatization, heat tolerance, Platygyra verweyi, Symbiodinium D1a, thermal-water discharge Received 5 January 2012; revision received 8 May 2012; accepted 18 May 2012 Introduction Coral reefs around the world are becoming increasingly exposed to the effects of climate change. These effects have resulted in increased incidences of breakdown of mutualistic symbioses between coral hosts and endo- symbiont dinoflagellates of the genus Symbiodinium, which constitutes part of the coral holobiont (Brown 1997). This process of breakdown is known as coral bleaching. The stability of coral ⁄ Symbiodinium symbio- ses is essential for maintaining the health of both corals and coral reefs and avoiding such breakdown. Coral bleaching has caused a worldwide decline in coral reefs (Hoegh-Guldberg et al. 2007; Knowlton & Jackson 2008) and is attributed to many factors, which include fluctu- ations in seawater temperature (Roberts et al. 1982; Muscatine et al. 1991; Brown et al. 1994; Fang et al. 1995; Fitt & Warner 1995; Gleason & Wellington 1995; Warner et al. 1996; Pandolfi et al. 2003; Saxby et al. Correspondence: Allen Chen, Fax: 886 2 27858059; E-mail: cac@gate.sinica.edu.tw Ó 2012 Blackwell Publishing Ltd Molecular Ecology (2012) doi: 10.1111/j.1365-294X.2012.05704.x