Bleaching and a Corallivore of the Coral Siderastrea radians in the Florida Keys

The tropical coral Siderasterea radians is typically found in mangrove areas, seagrass beds, and environments tolerated by few other scleractinians in the Caribbean and South Florida. Siderastrea radians experience bleaching stress in Buttonwood Sound in Florida Bay during April–May, a time when the seawater is below bleaching temperatures. Stress first appears as a pink coloration due to the presence of fluorescent pigments protecting the coral tissue and algal symbionts from exposure to excessive sunlight/UV light. Surveys of S. radians in areas frequented by parrotfish showed that up to 38.5% of the corals were pink, with about a quarter of all the corals having bite marks. In areas not frequented by parrotfish, only 3.2% of the corals were pink, and none had bite marks. A seasonal analysis in parrotfish-frequented seawater showed S. radians contained among the lowest tissue biomass and density of symbiotic algae during April–May 2010–2017, often looking pink. It is hypothesized that seawater temperature is not the cause of bleaching in Buttonwood Sound during April–May but rather predation by the rainbow parrotfish Scarus guacamaia.