Longitudinal variation in algal symbionts (zooxanthellae) from the Indian Ocean zoanthid Palythoa caesia

Single-celled, symbiotic, dinoflagellate algae known as zooxanthellae form associations with many shallow-water tropical marine invertebrates, Local ecological factors, particularly light levels, are known to influence algal type and distribution within hosts. Here I investigate whether biogeographic factors are similarly important in a convenient model, the zoanthid Palythoa caesia (Dana, 1846). Algal genotypes from P. caesia specimens from the eastern and western Indian Ocean were determined by restriction analysis and sequencing of the small subunit RNA gene, following PCR amplification with algal-specific primers. RFLP results indicate 2 common algal genotypes in the east, but only a single genotype in the west. Results from sequencing suggest further geographic patterning, with restricted geographic distribution of clades from the Seychelles, Sulawesi and Thailand.