Zoological Studies

Vol. 50 No. 4, 2011

Distribution Patterns of Five Zoanthid Species at Okinawa Island, Japan

Yuka Irei1,*, Yoko Nozawa2, and James D. Reimer3

1Molecular Invertebrate Systematics and Ecology Laboratory, Graduate School of Marine Science, Univ. of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan
2Biodiversity Research Center, Academia Sinica, Nankang, Taipei 115, Taiwan
3Molecular Invertebrate Systematics and Ecology Laboratory, Rising Star Program, Transdisciplinary Research Organization for Subtropical Island Studies (TRO-SIS), Univ. of the Ryukyus, Senbaru 1, Nishihara, Okinawa 903-0213, Japan

Yuka Irei, Yoko Nozawa, and James D. Reimer (2011) Zoanthids (Anthozoa, Hexacorallia) are distributed worldwide, especially in shallow tropical and subtropical waters. In fringing reefs of Okinawa I., southwestern Japan, zoanthids are common benthic organisms. Despite their abundance, even basic ecological information such as favorable habitats based on quantitative surveys is still lacking. Accordingly, we investigated the distribution patterns of 5 common zooxanthellate zoanthid species in shallow reef waters (< 10 m) of Okinawa I.: Palythoa tuberculosa, P. mutuki, Zoanthus sansibaricus, Z. kuroshio, and Z. gigantus. The survey was conducted using the belt transect method in 3 reef environments (moat, reef crest, and reef slope) at 10 reef sites in 2008. As a result, 2404 zoanthid colonies were observed, and Z. sansibaricus and P. tuberculosa were the 2 most dominant species, respectively comprising 52% and 41% of the total zoanthids observed. The environment where the highest numbers of colonies were observed was the reef crest (1615 colonies) followed by the reef slope (687 colonies), while zoanthids were rare in the moat environment (102 colonies). There were significantly more Z. sansibaricus colonies on reef crests than reef slopes, but no significant difference was seen in the frequencies of the other 4 species between the reef crest and reef slope. As to the zoanthid colony size, most colonies (> 86%) of the 5 zoanthid species were < 10 cm in diameter, and only 2 colonies of > 50 cm in diameter were observed in the survey. The absence of zoanthids in moats suggested that sedimentation or weak currents may be factors limiting zoanthid distribution; however, detailed investigations are necessary to confirm this. Since zooxanthellate zoanthids are a major benthic group on coral reefs, further research focusing on the relationships between zoanthid distribution and environmental conditions will foster a better understanding of coral reef ecosystems.

Key words: Zoanthid, Distribution, Shallow reef environment, Belt transect.

*Correspondence: Tel: 81-98-8958542. Fax: 81-98-8958577. E-mail:yuka.irei.mugi@gmail.com