Abstract: Zooxanthellae are very important for the coral reef ecosystem. The diversity of coral hosts is high in the South China Sea, but the diversity of zooxanthellae has not yet been investigated. We chose the Zhubi Coral Reef of the Nansha Islands as the region to be surveyed in the present study because it represents a typical tropical coral reef of the South China Sea and we investigated zooxanthellae diversity in 10 host scleractinian coral species using polymerase chain reaction (PCR) of the large subunit rRNA and restriction fragment length polymorphism (RFLP) patterns. Pocillopora verrucosa, Acropora pelifera, Acropora millepora, Fungia fungites, Galaxea fascicularis, and Acropora pruinosa harbor Clade C, Goniastrea aspera harbors Clade D, and Acropora formosa harbors Clades D and C. Therefore, the Clade C is the dominant type in the Zhubi Coral Reef of the Nansha Islands. Furthermore, the results of the present also disprove what has been widely accepted, namely that one coral host harbors only one algal symbiont. The coral-algal symbiosis is flexible, which may be an important mechanism for surviving coral bleaching. Meanwhile, on the basis of the results of the present study, we think that Symbiodinium Clade D may be more tolerant to stress than Symbiodinium Clade C.(Author for correspondence.Tel: 020 8446 0294; Fax: 020 8446 0294; E-mail: coral@scsio.ac.cn)

Key words: large subunit rDNA, restriction fragment length polymorphism, scleractinian corals, symbiotic dinoflagellates, Zhubi Coral Reef, zooxanthellae.