Estimating the Heritability of Plasticity of Thermal Tolerance and its Application in the Restoration of Endangered Caribbean Coral

Abstract Over the last two centuries anthropogenic activity has elevated atmospheric CO2, creating a greenhouse effect that is predicted to elevate global temperatures 1-4o C within the century. Increases in surface temperature pose a threat to the world’s coral reefs and have been the cause of many mass bleaching events. To combat this new threat, corals must migrate, acclimate, or evolve to rising temperatures. Phenotypic plasticity, or the ability of an individual to express different phenotypes to survive in different environments, is crucial for sessile organisms since it can increase survivability in species incapable of moving to better conditions. This project investigated the utility of plasticity with three questions: 1) Does phenotypic plasticity of thermal tolerance exist among endangered Caribbean corals? 2) To what extent are differences in the amount of phenotypic plasticity of thermal tolerance due to differences in coral genotype? 3) Can plasticity be utilized by managers to restore vulnerable reef zones? This study was conducted in two phases. The first utilized a raceway experiment to identify the presence of plasticity of thermal tolerance, as well as estimate Broad (H2) and Narrow-sense (h2) heritability of plasticity of thermal tolerance among Acropora cervicornis. The second phase incorporated the transplant of ambient and heat-treated Acropora cervicornis, Acropora palmata, and Orbicella faveolata fragments among shallow and deep reef zones in the Florida Keys. While a moderate degree of H2 was measured, h2was calculated as virtually non-existent among A. cervicornis fragments. The transplant study suggests depth has a more significant effect upon coral growth and viability than previous heat exposure, but thermal conditioning may still be useful for seasonal warming events. These findings have furthered the current understanding of phenotypic plasticity among and corals and may be useful to managers for future restoration efforts