Response of Moorea reef to marine heatwaves: spatiotemporal heterogeneity in geomorphology, water depth, and community dynamics

Most studies rely on course-resolution satellite-derived sea surface temperature (SST) data to analyze Marine Heatwaves (MHW) in coral reef regions, limiting their ability to capture fine-scale thermal variability. Our study integrated satellite SST with high-resolution in situ temperature and coral cover data from six sites across three geomorphic reef types (fringing reef, backreef, forereef) in Moorea reef. We examined the spatiotemporal patterns of MHW and coral cover dynamics from 2005 to 2024 and identified key drivers of coral variation. Results reveal a west-north-east gradient in MHW intensity around Moorea, with thermal stress being most severe in shallow fringing reef and attenuating with depth. Coral cover decline and recovery exhibited strong spatiotemporal heterogeneity, with lower mortality and recovery rates in shallow fringing reef and backreef compared to the forereef (10–17 m). Over the past decade, fringing reef recovery rates remained below 10%, while forereef recovery was higher at 10 m than at 17 m. Notably, no clear depth-dependent recovery pattern was observed in the fringing reef. Generalized linear mixed models confirmed coral cover correlates with thermal stress and water depth, with variation across geomorphic zones. By elucidating the interactions among reef geomorphology, depth, thermal stress, and coral cover, our findings provide a scientific foundation for targeted coral conservation strategies.