The rebound in coral cover could be undone by future mass bleaching events, as climate breakdown poses a “critical threat” to all reefs, the Australian Institute of Marine Sciences said.
Coral cover on two-thirds of Australia’s Great Barrier Reef has reached its highest level since records began 36 years ago, according to marine scientists monitoring the ecosystem.
But the coral remains highly vulnerable to mass bleaching events, which are occurring increasingly frequently as human activity warms oceans, the Australian Institute of Marine Sciences (AIMS) said in its annual report.
The recovery in the central and northern stretches of the UNESCO world heritage-listed reef did not extend to the southern region, which lost coral cover amid an outbreak of crown-of-thorns starfish.
The Great Barrier Reef remains a “resilient system” that “still maintains that ability to recover from disturbances,” AIMS monitoring programme leader Mike Emslie said.
“But the worrying thing is that the frequency of these disturbance events are increasing, particularly the mass coral bleaching events,” he added.
Earlier this year saw the first mass bleaching during a La Niña year, a natural climate cycle which typically brings cooler temperatures that allows the coral to recover. It was the fourth mass bleaching event in seven years.
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Dr Emslie said climate change was driving increasingly frequent and longer-lasting marine heatwaves.
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“The increasing frequency of warming ocean temperatures and the extent of mass bleaching events highlights the critical threat climate change poses to all reefs, particularly while crown-of-thorns starfish outbreaks and tropical cyclones are also occurring,” he said.
He warned: “Future disturbance can reverse the observed recovery in a short amount of time.”
AIMS chief executive Dr Paul Hardisty said the increasing frequency of such events is “uncharted territory” for the reef.
“In our 36 years of monitoring the condition of the Great Barrier Reef we have not seen bleaching events so close together,” he said.Share
A problem was encountered – please try again laterFears over Great Barrier Reef bleaching
The report comes as UNESCO considers whether to list the Great Barrier Reef as “in danger”, following a visit by the United Nations body in March.
The matter was due to be discussed at a meeting of the World Heritage Committee in Russia in June, which was then postponed.
In a key measure of reef health, AIMS defines hard coral cover of more than 30% as high value, based on its long-term
surveys of the reef.
On the northern region, average hard coral cover grew to 36% in 2022, while on the central region hard coral cover increased to 33% – the highest levels recorded for both regions since the institute began monitoring the reef in 1985.
But in the southern region, which generally has higher hard coral cover than the other two regions, cover fell to 34% in 2022 from 38% a year earlier.