Extensive coral bleaching and mortality in the central Red Sea during the fourth global coral bleaching event

Record-breaking ocean temperatures during the fourth global coral bleaching event in 2024 caused unprecedented heat stress in the central Red Sea. To assess ecological impacts, we quantified bleaching prevalence, coral mortality, and changes in scleractinian coral cover using in situ benthic transect surveys (5 m and 10 m depth) and monitoring of tagged coral colonies along a depth gradient (5 m to 25 m) on reefs spanning a nearshore-offshore gradient. Bleaching prevalence was high, with 90% (5 m) and 87% (10 m) of coral cover showing visible signs of bleaching in September 2024. In contrast to previous bleaching events in 2010 and 2015, which exhibited less bleaching on offshore reefs, bleaching prevalence was uniformly high on all reefs across the cross-shelf gradient. Overall, live coral cover declined by 65% (from 20% in August 2024 to 7% in January/February 2025), with the largest declines in branching Pocillopora and Acropora, decreasing by 98% (from 4.6% to 0.1%) and 100% (from 1.3% to 0.0%), respectively. Tagged colony data corroborated the severe decline of branching corals in shallow waters, with 100% mortality occurring up to 15 m depth and 0% mortality at 25 m, demarcating a clear depth limit of the heat exposure. The divergence in the spatial pattern of bleaching in 2024 compared to previous events and the magnitude of coral cover loss underscore the severity of this event and highlight the urgent threat climate change poses to reef function and resilience in the central Red Sea.