In May 2024, there was a catastrophic event of coral bleaching in the Southern Great Barrier Reef, resulting in a 44% death rate in protected regions. The fourth global coral bleaching event (GCBE4), which started in January 2023 and exceeded the bleaching levels of 2014–2017, was classified as a mass bleaching catastrophe brought on by heat stress. A fifth-largest widespread bleaching episode occurred in the GBR, affecting over 77% of the world’s reefs.

When heat stress causes corals to eject the symbiotic algae, zooxanthellae, the result is coral bleaching, which turns the corals white. Corals may withstand bleaching, but prolonged or severe stress frequently results in mortality.

Over 161 days, researchers observed 462 coral colonies at One Tree Reef. By February, 66% of the colonies were bleached; by April, that number had increased to 80%. By May, the mortality rate was 44%, and by July, it had risen to 53%.

Coral Mortality and Structural Collapse

The mortality rate for some coral genera, especially Acropora, reached 95% due to coral bleaching in the Southern Great Barrier Reef. With 69% of colonies impacted, bleaching also occurred in thermally resilient corals like Porites. Diseases like black band disease (BBD), which affected 66% of bleached colonies, increased the death rate.

By July, the reef’s structural disintegration was visible. The death rates for Acropora and Seriatopora corals were 95% and 100%, respectively. Parts of the reef were reduced to rubble when coral colonies collapsed, with branches breaking off and creating piles on the seafloor coated in algae.

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Call to Action and Research Significance

According to lead author Maria Byrne, the results highlighted how urgent it is to save coral reefs, which are essential for coastal protection, biodiversity, and food security. The southern GBR was severely affected by acute heat stress, even though it was protected.

Coral reef resilience is under extreme stress, according to Professor Ana Vila Concejo. She urged quick and efficient management measures to assist reefs in enduring the challenges brought by climate change. This study emphasizes how crucial it is to comprehend how coral reef ecosystems will change as a result of global warming and the necessity of taking preventative action to protect them.

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