New study suggests climate change is happening too quickly for corals to adjust
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Scientists at the University of Sydney have identified a devastating combination of coral bleaching and a rare necrotic wasting disease that wiped out large, long-lived corals on the Great Barrier Reef during the record 2024 marine heatwave.
The study, published in Proceedings of the Royal Society B, found that bleaching triggered by high ocean temperatures was followed by an unprecedented outbreak of black band disease, which killed vast swathes ofGoniopora corals, also known as flowerpot or daisy coral, at One Tree Reef on the southern Great Barrier Reef.
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‘This research shows that the compounding impact of disease – which appeared after the onset of bleaching – is what killed the Goniopora. These are very long-lived corals that would normally survive bleaching,’ said Professor Byrne, a professor of marine biology in the School of Life and Environmental Sciences.
The team tracked 112 Goniopora colonies across a year, finding that three-quarters had died by October 2024, while only one quarter showed partial recovery. Surveys of more than 700 colonies showed the same pattern – widespread bleaching, the presence of black band disease and high incidences of mortality.
Black band disease is a bacterial infection able to infect living coral, forming a black band that crosses the infected coral, usually killing the colony. While common in Caribbean reefs, it is rare to see in Australian waters. Its sudden appearance in One Tree Reef’s marked the first recorded epidemic event of this kind on the Great Barrier Reef.
The 2024 El Niño weather event brought the highest sea temperatures on record to the Great Barrier Reef, with marine heatwave conditions lingering for months. During this time, 75 per cent of Goniopora colonies at One Tree Reef bleached. Initially, just four per cent showed signs of black band disease – by April, however, the disease had spread to more than half the bleached colonies.
‘Normally these massive corals withstand environmental stress, but the combination of record heat and infection was catastrophic,’ said Dr Shawna Foo, an ARC DECRA Fellow in the School of Life and Environmental Sciences. ‘It’s a stark example of how multiple stressors can act together to undermine reef resilience.’
Such findings highlight the importance of long-term in-water monitoring made possible by the University’s One Tree Island Research Station, which provides vital infrastructure for studying coral ecosystems under natural conditions.
The researchers conducting the study have also sent a stark warning out: ‘The current trajectory of climate change is progressing too quickly for corals to adjust,’ the authors write. ‘Coral reefs are in danger, with recurrent anomalous heatwaves and mass coral bleaching being the greatest threat to their survival.’
According to Professor Byrne, the loss of these large corals will have lingering impacts on reef biodiversity, coastal protection and food security.
‘Coral reefs support more than a billion people worldwide. What we’re witnessing is a collapse in the natural resilience of these ecosystems. Ambitious global action to reduce emissions is now the only path to their survival.’
