Bleaching in subtropical corals of the northern South China Sea: differential susceptibility to environmental stressors and molecular mechanisms

Recent studies indicate that subtropical coral communities can serve as refuges of global environmental change, but the relative susceptibility of subtropical species to environmental stressors and the underlying mechanisms of stress responses are largely unknown. Here we propose to study the effects of high temperature and low salinity on subtropical corals in the northern South China Sea. These two environmental stressors have been known to cause bleaching in these subtropical corals in recent years. We propose to construct an exposure system for determining coral bleaching thresholds, select nine species of common corals of different growth forms and expose them to a combination of thermal and salinity treatments in the laboratory to determine their bleaching thresholds. For the two most sensitive and two most resistant species, a laboratory experiment will be conducted to compare their physiological and transcriptomic responses to temperature and salinity stresses, followed by gene co- expression network analysis and positive selection analysis to identify underlying mechanisms of stress responses. Overall, our study will determine the potential coral “winners and losers” of global environmental change in the northern South China Sea for the first time, uncover molecular mechanisms of coral bleaching considering coral as a holobiont of coral host and its symbionts, and develop a set of diagnostic biomarkers of coral thermal/salinity stress. The results will help direct resources for a better management of subtropical coral ecosystems.