ABSTRACT
The majority of reef corals, as well as other reef-dwelling cnidarians, are inhabited by symbiotic dinoflagellates of the genus Symbiodinium (Muscatine 1990). The gorgonian soft corals (Isis) also have Symbiodinium in their tissue (Fabricius and Alderslade 2001). The dependence of the coral animals upon the photosynthetic activities of endosymbiotic Symbiodinium living within their endodermis tissue (Barnes and Chalker 1990) restricts the distribution of these coral animals to sunlit waters (Veron 1993). The photobionts supply nutrients to their hosts, which allow them to colonize habitats they normally could not because of limited supplies of food (Paracer and Ahmadjian 2000).
