Word on the reef is in – and it’s grim. A peer-reviewed study (the first of its kind) by a team of marine scientists from The University of Sydney paints a stark picture of the state of the southern Great Barrier Reefs: In early 2024, marine heatwaves left coral colonies bleached at “catastrophic levels”. 

IMAGES COURTESY OF THE UNIVERSITY OF SYDNEY / ABOVE: Bleached Acropora table coral, One Tree Island Reef, April 2024.

ABOVE: One Tree Island reef ‘gutter’ coral pre-bleaching – April 2022

Led by Professor Maria Byrne from the School of Life and Environmental Sciences, the research highlights the alarming impact of unprecedented marine heatwaves on coral ecosystems, raising urgent concerns for marine biodiversity and the communities that depend on these vital ecosystems.

The study, published in Limnology and Oceanography Letters, provides critical insights into the extent of coral bleaching and mortality during the 2023-2024 global marine heatwave. The research team meticulously tracked the health of 462 coral colonies at the University of Sydney’s Great Barrier Reef research station at One Tree Island over a period of 161 days.

The results revealed that 66% of the colonies were bleached by February 2024 and 80% by April. By July, 44% of the bleached colonies had died, with some coral experiencing a staggering 95% mortality rate.

Coral reefs aren’t just biodiversity hotspots, but also crucial for food security and coastal protection, says Professor Maria Byrne, lead author of the study. “Our findings underscore the urgent need for action to protect coral reefs. The southern Great Barrier Reef, despite its protected status, was not immune to the extreme heat stress that triggered this catastrophic bleaching event.”

ABOVE: Acropora and Porites bleached coral at One Tree Island Reef, April 24.

Professor Ana Vila Concejo, a co-author of the study from the School of Geosciences, said: “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 prioritise strategies that enhance their ability to withstand climate change. Our findings underscore the need for immediate and effective management interventions to safeguard these ecosystems.”

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 prioritise strategies that enhance their ability to withstand climate change.

The implications of this research extend beyond the ecology and conservation. Coral reefs provide essential services to human communities, including fisheries, tourism and coastal protection. As the Great Barrier Reef faces increasing threats from climate change, the study calls for a collaborative approach to conservation that involves local communities, scientists and policymakers.

Dr Shawna Foo, a Sydney Horizon Fellow and co-author of the study, said: “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 heatwave, its role in facilitating recovery will be crucial to observe.”

ABOVE L-R: Professor Ana Vila Concejo on the Great Barrier Reef, University of Sydney Horizon Fellow Dr Shawna Foo, and Professor Maria Byrne on the Great Barrier Reef.

But this isn’t a story of giving up – this is a rallying cry. 

Yes, the situation is dire, but it’s also a reminder of why we can’t stop fighting for our reefs and the communities (both human and non-human) that depend on them. The reef has shown resilience before, and with our help, it can again. You can help by supporting groups like Reef Restoration Foundation, Great Barrier Reef Foundation, Tangaroa Blue Foundation, or Australian Marine Conservation Society.  And as always, keep advocating for strong climate policies.