Genotypic diversity of symbiotic dinoflagellates associated with hermatypic corals from a fringing reef at Sesoko Island, Okinawa

Abstract

The genotypes of zooxanthellae associated with eight scleractinian corals and one hydrocoral from a fringing reef of Sesoko Island (Okinawa, Japan) were determined using the single stranded conformational polymorphism (SSCP) of large subunit ribosomal DNA (28S rDNA). Preliminary RFLP analysis of small subunit (18S) rDNA showed that four pocilloporid corals harbored zooxanthellae of clade C, except one branch of Stylophora hystrix kept at 8% light which contained zooxanthellae of clade A and C. The hydrocoral Millepora intricata harbored zooxanthellae of clade A and C. RFLP analysis failed to distinguish three morphophysiological types described by Titlyanov et al. (2001a, b). SSCP analyses of 28S rDNA showed that zooxanthellae from the nine coral species gave at least fourteen distinct SSCP patterns. While zooxanthellae from S. hystrix and S. caliendrum had identical SSCP patterns, SSCP patterns of zooxanthellae from other coral species studied were distinct from each other. In six out of nine coral species, branches from the same colonies kept under different light conditions contained zooxanthellae that showed different SSCP patterns. However, no clear relationship was found between zooxanthellae genotypes and light intensity. The present results suggest that three morphophysiological types are not unique but that each type consists of zooxanthellae of several genotypes.