The impact of the 2024 coral bleaching event on corals at a remote atoll in the Tuamotu Archipelago, French Polynesia

Abstract Coral reefs are under severe threat from global warming, particularly due to the increasing frequency of mass coral bleaching events. This study documents the effects of the fourth global coral bleaching event on corals of Tahanea, a remote uninhabited French Polynesian atoll over a 10-month period. Coral surveys (transects and tracking of individual colonies) and temperature monitoring were conducted by one in situ observer. The marine heatwave lasted 80 days, from January 24, 2024, to April 12, 2024, with a peak intensity of + 1.55 °C above climatological levels. This event was the longest in the past 30 years in the South Pacific region as well as the most intense in terms of cumulative intensity (79.2 °C·days) and daily degree heating week (DHW) annual maximum (reaching 4.7 °C weeks −1 ). In May 2024, 11–16% of coral colonies showed signs of bleaching, while 27–43% were recently dead. By September, out of the 40 studied large colonies, 50% of corals partially bleached in April were dead, and 80% of those fully bleached in April had died. In September 2024, underwater visual surveys (depth: 0.4–2 m) revealed low live coral cover (15%), with old dead coral dominating substrate composition at Tahanea. This study shows that even isolated, uninhabited coral reefs, far from any direct human pressure, are highly vulnerable to marine heatwaves. This highlights the importance of rapid and drastic reductions in greenhouse gas emissions to conserve coral reefs.