Thermal Resilience of Corals in the Southern Egyptian Red Sea Reefs

The Red Sea, particularly its northern region, has long been regarded as a thermal refuge for coral reefs due to their remarkable resilience to elevated sea surface temperatures associated with climate change. However, this perception has been increasingly challenged by recent mass bleaching events recorded in 2012, 2020, 2023, and most recently in 2024. This study systematically evaluated coral resilience patterns following the September 2023 mass bleaching event along the southern Egyptian Red Sea coast. During the summer of 2023, prolonged marine heatwaves in the northwestern Red Sea (Egyptian coast) triggered a severe bleaching event, with sea surface temperatures (SST) exceeding the summer monthly maximum mean (MMM; ≥32°C), the established bleaching threshold, from July to October. Post-bleaching assessments revealed significant interspecific and colony-level variability in resilience. While some corals exhibited full recovery, others suffered high mortality, with site-specific recovery rates ranging from 34 to 56%. Massive corals, particularly Porites, demonstrated the highest resilience (82% recovery), whereas branching genera such as Acropora and Stylophora showed the lowest recovery rates (29–31%) and the highest mortality (52% for Acropora sp.). Surprisingly, depth (2– 10m) and cross-shelf position (inshore vs. offshore) had minimal influence on recovery outcomes, suggesting that coral responses were primarily shaped by species-specific traits, microbiome composition, and local environmental conditions. Despite the Red Sea’s reputation as a thermal refuge, the 2023 event underscores that even thermally tolerant reefs are highly vulnerable to prolonged heat stress. These findings highlight the urgent need for targeted conservation strategies, including microbiome-assisted resilience interventions, to safeguard these critical ecosystems in the face of intensifying climate-driven bleaching events.