Outcomes of the fourth global coral bleaching (2023–2024) in the Maldives

Abstract The fourth global coral bleaching event (2023–2024) was the most extensive and intense ever recorded, driven by unprecedented marine heatwaves. In the Maldives, one of the largest atoll systems in the Indian Ocean, the 2024 thermal anomaly reached record sea surface temperatures (31.5 °C) and degree heating weeks exceeding 9 °C-weeks, indicating cumulative stress levels above the mortality threshold for most coral taxa. We assessed the ecological impacts of this event across 18 reefs in central and southern atolls, comparing benthic community structure before and after bleaching. In the central atolls, live hard coral cover dropped by > 40% on average; the highest mortality (57%) occurred on a lagoon reef in Ari Atoll and disproportionately impacted branching and tabular Acropora . These losses resulted in a shift towards massive and encrusting corals and a marked reduction in structural complexity. In contrast, reefs in the southern Huvadhoo Atoll showed no detectable mortality and, instead, exhibited increased coral cover (+ 12–23%), dominated by Acropora and Pocillopora , indicating high resistance and recovery capacity. The 2024 event matched the spatial extent of the 2016 bleaching but approached the intensity of the 1998 mass bleaching, setting a new ecological benchmark for the region. The pronounced north–south gradient in bleaching severity underscores the influence of local environmental conditions and anthropogenic pressures in modulating coral vulnerability. Identifying and protecting resilient southern reefs as climate refugia is essential to preserving biodiversity and maintaining reef ecosystem functions in a rapidly warming Indian Ocean.