Catastrophic bleaching and mortality of corals during the fourth global bleaching event in Marine Protected Areas, Kenya

As anthropogenic climate change drives sea surface temperatures (SST) to unprecedented levels, the increasing frequency of mass bleaching threatens the structural integrity of coral reefs ecosystems vital to Kenya’s coastal protection and blue economy. During the 2024 fourth global coral bleaching event, extreme marine heatwaves triggered widespread impacts across diverse coral genera within Kenya’s Marine Protected Areas (MPAs). This study provides the first systematic assessment of large-scale coral bleaching and immediate mortality across four key Kenyan fully protected MPAs: Kisite, Mombasa, Malindi, and Watamu following the extreme 2024 thermal anomaly peak. We utilized NOAA Coral Reef Watch satellite-derived sea surface temperatures (SSTs) and Degree Heating weeks (DHW) to confirm thermal stress, alongside in situ benthic surveys to quantify bleaching severity and mortality across dominant coral genera.

Analysis revealed record-breaking heat stress peaking at 11 DHW, with SSTs exceeding 32°C (2.5°C above baseline). Spatial variation in bleaching severity was significant: Kisite exhibited the highest Bleaching Mortality Index (47.8%), followed by Malindi (41.3%), Mombasa (37.6%), and Watamu (36.3%). While thermally susceptible genera (Pocillopora, Acropora) were heavily impacted (50–60%), typically tolerant massive corals (Porites, Goniastrea) also exhibited severe bleaching (up to 55%) in northern MPAs. Notably, southern MPAs showed higher overall bleaching prevalence (87%), but northern MPAs suffered significantly higher immediate mortality (29% vs. 12.9%).

This pronounced spatial variability reflects a complex interplay between thermal stress, reef geomorphology, and water quality. These findings demonstrate the rising vulnerability of even historically resilient taxa within fully protected zones. This research underscores the critical need for continuous monitoring to identify thermal refugia and predict community shifts, providing essential evidence to guide Kenya’s adaptive coral restoration and climate-resilience strategies.