Regional and genus-specific factors underpin bleaching variation across India’s corals reefs during the fourth global coral bleaching event — UC Berkeley

Between 2023 and 2025, over 80% of tropical coral reefs experienced extreme levels of heat stress coinciding with the El Niño of 2023, and resulting in the 4th global mass coral bleaching event. Despite having multiple reef regions, data on the impacts of mass bleaching events on coral reefs across South Asia is sparse. Through a coordinated, nationwide collaboration of scientists and citizen observers, we assessed bleaching responses across five reef regions in India, spanning most of the subcontinent’s major reef areas, from oceanic atolls to mainland fringing and patchy reef formations. While bleaching intensity increased with accumulated heat stress (DHW) as expected, it showed distinct regional variability, revealing the limits of DHW as a universal predictor. Among the regions, Lakshadweep was the most affected with up to 37% coral cover bleached or dead at intermediate DHW. In contrast, MGMNP faced only 11.5% bleaching or mortality, likely reflecting regional oceanic processes that could create mesoscale thermal refugia. Across regions, Acropora, Pocillopora, Galaxea, and Montipora, were the most affected genera, while Pavona, Platygyra, Goniastrea, and Favites were among the least affected. Palk Bay displayed a reversal of canonical genus-level susceptibilities, with only modest bleaching or mortality of 13.6% in the ordinarily vulnerable Acropora colonies, but 61.8% mortality in the ordinarily resistant Porites colonies. These contrasting regional and taxonomic responses indicate how context-specific resistance patterns, and local oceanography may mediate thermal stress and underscore the need to integrate these local geographical contexts in our understanding of bleaching impacts on tropical reefs.