ORIGINAL ARTICLE Biology Genetic variations within Symbiodinium clade C among zooxanthellate corals (Scleractinia) in the temperate zone of Japan Yi-Ting Lien • Hironobu Fukami • Yoh Yamashita Received: 26 November 2012 / Accepted: 24 March 2013 Ó The Japanese Society of Fisheries Science 2013 Abstract In a recent study most of the temperate-living corals were found to harbor stress-sensitive Symbiodinium clade C, which is common in the tropical zone. In this study, we investigated the genetic variations within Sym- biodinium clade C among corals living in temperate waters of Japan (17 genera; 26 species) using rDNA internal transcribed spacers (ITSs) to clarify the genetic differences between climatic zones. We also focused on two wide- spread coral species, Acropora hyacinthus and Pocillopora damicornis, to compare the genetic differences of Symbi- odinium clade C between subtropical and temperate regions. We found multiple haplotypes of Symbiodinium ITSs in clade C, which formed nine subclades. Our data indicate that five genera (Acropora, Cyphastrea, Styloco- eniella, Porites, Pocillopora) contained host-specific Symbiodinium, while members of the family Faviidae and others contained several Symbiodinium ITS haplotypes from two or three subclades. A comparative analysis using Acropora and Pocillopora also revealed that the temperate zone coral population formed a single subclade of Symbiodinium clade C that was genetically isolated from those of subtropical populations. In summary, the majority of corals living in temperate waters of Japan, such as faviid corals, have several ITS haplotypes which possibly are utilized as an opportunistic survival strategy under severe environmental conditions, whereas Acropora and Pocillo- pora at the very least harbor temperate zone-specific Symbiodinium. Keywords Regional differences Á Symbiodinium Á Endosymbiotic algae Á Internal transcribed spacers Á SSCP Introduction Zooxanthellate scleractinian corals (referred to as corals hereafter) are abundant in waters of the tropical and sub- tropical oceans. In Japan, more than 300 coral species have been reported in the coral reefs around the Ryukyu Islands (24–26°N). Approximately 100 coral species have also been reported at higher latitudes (30–35°N, referred to as the temperate region hereafter) in Japan, where coral reef structures are not formed [28, 48]. It has been suggested that continuous supplies of coral larvae that are transported by the Kuroshio current from tropical to temperate regions have maintained coral populations in the temperature waters of Japan [52]. Unlike tropical and subtropical zones, temperate zones are characterized by relatively lower irradiance and lower seawater temperatures, which can be a challenge to the survival of corals and their endosymbiotic algae (zooxan- thellae), especially during the winter season. For example, the average water temperature during the coldest month is lower than 18 °C in the temperate region of Japan [22, 27, 32]. Thus, rather than coral larvae being supplied from Electronic supplementary material The online version of this article (doi:10.1007/s12562-013-0623-8) contains supplementary material, which is available to authorized users. Y.-T. Lien Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan Y.-T. Lien Á Y. Yamashita Field Science Education and Research Center, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan H. Fukami (&) Faculty of Agriculture, University of Miyazaki, 1-1 Gakuen-kibanadai Nishi, Miyazaki 889-2192, Japan e-mail: hirofukami@cc.miyazaki-u.ac.jp 123 Fish Sci DOI 10.1007/s12562-013-0623-8 Author's personal copy