Coral bleaching occurrence and its relation to marine heatwave events in the Southwestern waters of South Sulawesi, Indonesia, as part of the Coral Triangle region

This study investigates the escalating threat of marine heatwaves (MHWs) to coral reef ecosystems in the southwestern waters of South Sulawesi, Indonesia. Based on four decades of data from 1982 to 2021, our analysis reveals a substantial increase in both the frequency and intensity of MHWs, with particularly severe events occurring in 2010, 2013, 2016, 2019, and 2020. The 2016 MHW was especially devastating, marked by extreme thermal stress and prolonged duration, reaching up to 215 days in the Lesser Sunda Islands. This event closely aligned with widespread Bleaching Alert Level 2 warnings in regions such as Lombok, indicating a high risk of coral mortality. The Coral Reef Health Index (CRHI) proved to be a valuable tool for reef assessment, showing strong positive correlations with coral cover (r = 0.83) and seagrass cover (r = 0.74), along with a strong negative correlation with rubble cover (r = −0.82). These results highlight the crucial role of reef structure and benthic composition in sustaining ecosystem health. In addition, the observed delay between peak MHW conditions and the occurrence of bleaching events emphasizes the need for real-time, high-resolution monitoring systems that integrate multiple observation methods. Our findings underscore the urgency of implementing comprehensive conservation strategies. These should include global actions to reduce ocean warming and targeted local efforts such as protecting reefs with high CRHI values, minimizing local stressors, and enhancing the effectiveness of marine protected areas. Future research should prioritize the integration of long-term field surveys with advanced remote sensing technologies and the inclusion of a wider range of oceanographic variables such as water quality and ocean acidification. Such approaches are essential for generating actionable data that support adaptive management and the sustained conservation of coral reef ecosystems.