Coral bleaching on Great Barrier Reef reaches 'catastrophic' levels - Oceanographic
Climate change

Coral bleaching on Great Barrier Reef reaches 'catastrophic' levels

Climate change

Coral bleaching on Great Barrier Reef reaches 'catastrophic' levels

A new study has revealed the 'catastrophic' level of coral bleaching on the protected southern Great Barrier Reef in early 2024, highlighting the need for immediate climate action.

22/01/2025
Words by Nane Steinhoff
Photographs by Maria Byrne/The University of Sydney

Just after we reported on the Great Barrier Reef’s shifting biodiversity due to the impact of climate change and human-caused pressures, researchers from the University of Sydney have now published the first peer-reviewed study documenting the “devastating impact” of coral bleaching across the southern Great Barrier Reef in 2024.

The study, published in Limnology and Oceanography Letters, puts a focus on the impact of marine heat waves on coral ecosystems, while providing insights into the extent of coral bleaching and mortality during the 2023–2024 global marine heat wave. 

Led by Professor Maria Byrne from the School of Life and Environmental Sciences, the research tracked the health of some 462 coral colonies at the University of Sydney’s Great Barrier Reef research station at One Tree Island over a period of 161 days. 

By February 2024, it was revealed that 66% of the monitored colonies were bleached. By April, that had jumped to 80%. Further investigation discovered that within just three months, by July 2024, 44% of those bleached colonies had died. One coral species in particular, the iconic Acropora coral, experienced an astonishing 95% mortality rate during this time.

“Our findings underscore the urgent need for action to protect coral reefs, which are not only biodiversity hotspots but also crucial for food security and coastal protection,” said Professor Byrne. “The southern Great Barrier Reef, despite its protected status, was not immune to the extreme heat stress that triggered this catastrophic bleaching event.”

The study delves deeper into the complex relationship between heat stress and coral disease. During the same time frame, Goniopora corals – for one example – were observed to develop black band disease which, in turn, contributed to the species’ high mortality rate.

“This research is a wake-up call for policymakers and conservationists. The resilience of coral reefs is being tested like never before, and we must prioritize strategies that enhance their ability to withstand climate change. Our findings underscore the need for immediate and effective management interventions to safeguard these ecosystems,” said Professor Ana Vila Concejo, a co-author of the study from the School of Geosciences.

Dr. Shawna Foo, a Sydney Horizon Fellow and co-author of the study, added: “Seeing the impacts on a reef that has largely avoided mass bleaching until now is devastating. The high rates of mortality and disease, particularly in such a remote and pristine area, highlight the severity of the situation. Although the reef’s highly protected status may not have prevented the impacts of the heat wave, its role in facilitating recovery will be crucial to observe.”

Read the full study here

Click here for more from the Oceanographic Newsroom.

Words by Nane Steinhoff
Photographs by Maria Byrne/The University of Sydney

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