Marine invertebrate diversity in the oceanic Ogasawara Islands: a molecular examination of zoanthids (Anthozoa: Hexacorallia) and their Symbiodinium (Dinophyceae)

Abstract

The Ogasawara (Bonin) Islands are oceanic islands approximately 1000 km south of mainland Japan noted for their high levels of both terrestrial and marine endemicity. Despite their unique location, the marine fauna of many taxa remains relatively under-examined. In this study, we specifically investigated the diversity of shallow water zoanthids (Cnidaria: Anthozoa: Hexacorallia) and their symbiotic zooxanthellae (Symbiodinium spp.) of the Ogasawara Islands for the first time. Using in situ field examinations combined with DNA sequencing and phylogenetic analyses, our results show the presence of five zoanthid species in the Ogasawara Islands; Zoanthus sansibaricus, Z. kuroshio, Palythoa tuberculosa, P. mutuki, and one potentially undescribed species of Palythoa. While most collected specimens were in symbiosis with clade C Symbiodinium as seen in southern Japan and other Indo-Pacific locations, one specimen of Z. kuroshio was unexpectedly in symbiosis with clade A, and no Z. sansibaricus colonies contained specific C1z type zooxanthellae previously observed at other locations. Overall, the Ogasawara Islands showed a lower zooxanthellate zoanthid species diversity (n = 5) than the non-oceanic Okinawa Islands (n > 10), which are at roughly the same latitude. Instead, the islands’ relatively depauperate zoanthid/symbiont fauna more closely resembles that of the northern Izu Islands.

Key words:

• Kuroshio recirculation
• Ogasawara (Bonin) Islands
• Palythoa
• Symbiodinium
• zoanthid
• Zoanthus
• zooxanthellae

Acknowledgements

Sampling in the Ogasawara Islands was made possible by a permit for collection of aquatic organisms by scuba diving from the Government of Tokyo (#21–12). In Ogasawara, Mr Tetsuro Sasaki (Institute of Boninology) greatly helped with logistics. Mr Tadao Sato and Mr Nobuyuki Niijima (Captain, Kaiyou Maru) of the Japan Fisheries Cooperatives, Ogasawara-jima aided in sample collection. Dr Hiroyuki Tachikawa (Natural History Museum and Institute, Chiba) gave us invaluable advice on the Ogasawara Islands, and Dr Ryuji Asami (University of the Ryukyus) helped with discussion of the Kuroshio Current. Dr Takuma Mezaki (Biological Institute on Kuroshio) informed us on the nature of zoanthid egg bundles. FS was partially supported by a Japan Society for the Promotion of Science (JSPS) post-doctoral fellowship (#P07812). JDR was supported in part by the Rising Star Program at the University of the Ryukyus, and a JSPS ‘Wakate B’ (# 21770089) grant-in-aid. KY was supported in part by a Research Institute of Marine Invertebrates Foundation (RIMI) grant. Two anonymous reviewers’ comments greatly improved this manuscript.

Associate Editor: Peter Hayward