The Great Barrier Reef has withstood the threats posed by coral bleaching events, predatorial crown-of-thorns starfish and other hazards this year, but remains precariously placed, according to an annual survey of hard coral coverage.
The Australian Institute of Marine Science’s (AIMS) annual long-term monitoring update observed a less than 1% decline in overall hard coral cover, with the southern part of the reef between Prosperine and Gladstone holding up best among three study regions.
But while coral cover remains higher than record lows recorded in the past decade, and continues to improve in several individual reefs, more substantial coral loss in others contributed to the small decline across the entirety of Great Barrier Reef.
Last year’s mass bleaching event – the first observed during a La Niña year since the survey began 37 years ago – also contributed to coral death, particularly in the GBR’s northern and central regions.
AIMS scientists found that while the 2022 bleaching was less damaging than in past events, its impact – combined with those of crown-of-thorns starfish and disease – contributed to the slight decline in hard coral across the GBR.
About 82% of individual reefs had 10-50% hard coral coverage, and a further 16% had more than 50% coverage.
Despite this, AIMS warned most of the recent recovery had been driven by fast-growing Acropora shield corals. These are particularly susceptible to cyclones, bleaching and crown-of-thorns starfish.
In a statement, the federal government’s Reef Authority described the reports of similar hard coral coverage to 2022 as “good news for the Reef”, with its acting Chief Scientist Dr Roger Beeden saying “While these local pressures have meant that average hard coral cover has plateaued, it also shows that in the absence of disturbances, reefs continue to recover”.
Coral reef ecologist and leader of the long-term monitoring program, Dr Mike Emslie, says the 2022 bleaching event didn’t cause widespread mortality but “it’s still under the threat of impacts that can quickly reverse the gains in a short amount of time”.
“Coral cover [recovery] can resume as long as there’re no future impacts from disturbances.”
Marine biologist Dr Emma Camp, who leads the Future Reefs program at UTS, also warns that while the resilience of the reef is encouraging, the long-term monitoring program provides only one snapshot of reef health.
“The Reef has an impressive ability to recover if given the chance, but importantly that there are differences between how individual reefs are faring,” Camp says.
“Caution must be noted as the report is based on coral cover which is only one metric of coral heath and function. Coral diversity for example is key to system resilience but not reported.”
Emslie says that the strength of the reef will be further tested by longer-term impacts of climate-driven disturbances, and reinforces the need to reduce greenhouse gas emissions driving increased global temperatures.
In 2018, the Intergovernmental Panel on Climate Change found coral reefs are one of the most vulnerable ecosystems on the planet, particularly from human disturbance and coral bleaching driven by ocean warming.
“The Great Barrier Reef is still a wonderful, vibrant place, it still can recover at the moment, it has the ability and resilience to recover from disturbances,” Emslie says, “But we’ve also got to temper that by the realisation, that we’re seeing increasing frequency of these disturbances, which is shortening the amount of time available for recovery.
“Predictions are that these particular climatically-driven disturbances are only going to be coming more frequently and probably more severely.”
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The Ultramarine project – focussing on research and innovation in our marine environments – is supported by Minderoo Foundation's Flourishing Oceans initiative.