Interspecific comparison of the symbiotic relationship in corals with high and low rates of bleaching-induced mortality

Some coral species are more resistant than others to environmental factors that cause bleaching and bleaching-related mortality. This study compared aspects of the coral/zooxanthellae symbiosis in species and genera that suffered either high or low mortality during a bleaching event. These characteristics were assessed in Okinawa between March and June 1999, 5-10 months after the bleaching event there in August-September 1998. Species with low mortality rates generally had higher densities of zooxanthellae per square centimeter and a very low rate of release of degraded zooxanthellae. Low-mortality species also had more total coral tissue per square centimeter of coral surface area. The size of zooxanthellae varied little among species. The differences in these characteristics among coral species suggest that the symbiotic relationship operates very differently among coral species.