Specificity of Symbioses Between Marine Cnidarians and Zooxanthellae

Abstract

The dinoflagellate zooxanthella, Symbiodinium (=Gymnodinium) microadriaticum Freudenthal, is harbored by more than 80 species of marine cnidarians, tridacnids and protists (Taylor, 1974). It is the only described zooxanthella species found in benthic symbiotic cnidarians. Its large host distribution is exceptional among algal symbionts of invertebrates (Taylor, 1974; Hollande and Carré, 1974; Karakashian, 1975). This wide phylogenetic range for a single species of zooxanthella suggests that the morphological and ultra-structural criteria used for its identification (Freudenthal, 1962; Kevin, et al., 1969; Taylor, 1969) might not distinguish between varieties of S. microadriaticum with narrower host or ecological distributions. This paper describes a series of studies using other methods to characterize genetic variation and specificity among isolates of S. microadriaticum.