Vulnerability of Indian coral reefs to marine heatwaves: Assessing the explanatory efficiency of thermal metrics

Marine heatwaves (MHW) are widely documented for their impacts on marine ecosystems of world oceans, but are rarely incorporated into the coral bleaching monitoring framework. In this study, we assessed the effectiveness of MHWs in explaining coral bleaching events in Indian seas, compared to the commonly used degree heating weeks (DHW) methodology. We found that even though DHW successfully explained the large-scale coral bleaching events associated with extreme climatic events like El-Nino, it failed to account for most of the small-scale coral bleaching events, which MHWs explained more effectively. Based on the analysis of historic coral bleaching events in Andaman and Nicobar, Gulf of Mannar, and Lakshadweep reefs in India, it was evident that the MHW parameters were effective in explaining the bleaching events, that DHW failed to capture. Due to this efficiency in explaining small-scale, regional coral beaching events as observed in Lakshadweep and Gulf of Mannar, we propose the inclusion of MHW parameters as a thermal stress metric in coral bleaching studies along with DHW. Incorporating MHWs into the current coral bleaching alert framework will improve the regional coral bleaching monitoring capabilities, providing a robust empirical baseline for future coral bleaching prediction approaches.