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Catastrophic bleaching in protected reefs of the Southern Great Barrier Reef
First published: 16 January 2025
Maria Byrne, Alexander Waller, Matthew Clements, Aisling S. Kelly, Michael J. Kingsford, Bailu Liu, Claire E. Reymond, Ana Vila-Concejo, Monique Webb, Kate Whitton, Shawna A. Foo
Abstract
The iconic Great Barrier Reef (GBR) experienced mass coral bleaching in early 2024. In the southern GBR, heat stress triggered severe and widespread bleaching to levels not previously recorded and impacted a diverse range of coral genera at One Tree Reef (OTR). Over 161 d, we tracked the health of 462 coral colonies from heatwave peak to autumn and winter cooling. In February and April, 66% and 80% of the colonies were bleached, respectively. By May, 44% of the bleached colonies were dead and 53% in July. In July, 31% of colonies were still bleached and 16% recovered. Goniopora developed black band disease contributing to high mortality. Colony collapse occurred in Acropora (95% mortality) with accumulation of algal-fouled fragments. In-water tracking of individual colonies showed rapid bleaching, disease onset and mortality. The protected status and offshore location did not protect OTR from heat stress bleaching and mortality.
Scientific Significance Statement
Ocean heating is causing mass coral bleaching, raising concern for a vast diversity of species that depend on coral reefs to exist and for the significant services coral reefs provide to humanity including food security and shoreline protection. The 2023-2024 global marine heatwave was extreme in triggering coral bleaching and high mortality. The drivers of coral death, rapid demise by heating or slow decline due to starvation by bleaching are a challenge to discern. Coral mortality data are scarce, particularly with respect to taxonomic detail. Our observations on initial responses to an intense marine heatwave show rapid bleaching, disease onset and mortality in diverse corals including genera that are considered resilient. This information is essential to predict how the species composition of coral reef ecosystems will change in a warming world. ...