The Great Barrier Reef was hit by a sixth widespread coral bleaching event since 2016 this summer – the second time the world’s biggest coral reef has seen the phenomenon strike in back-to-back years – according to government authorities.
Scientists and conservationists reacted with dismay that widespread bleaching – driven by global heating – was becoming normalised, with one saying Australia’s next term of government may be the natural wonder’s last shot at survival.
“It’s awful,” said Prof Tracy Ainsworth, of the University of New South Wales and vice-president of the International Coral Reef Society.
“The impact to the reef of these consecutive and severe bleaching events now for a decade is fundamentally changing nature and the reef ecosystem.”
The Great Barrier Reef Marine Park Authority released an update on Wednesday saying data suggested the reef had experienced “widespread coral bleaching” across the north and far north.
“This event is the sixth since 2016 and, while less extensive than the coral bleaching event in 2023–24, it is the second time the reef has experienced widespread bleaching events across consecutive summers,” the update said.
The authority said in an accompanying report that the “severe and widespread coral bleaching” had been caused by marine heatwaves driven by the climate crisis.
Quick Guide
What is coral bleaching?
Show
Coral bleaching describes a process whereby the coral animal expels the algae that live in its tissues and give it its colour and much of its nutrients.
Without its algae, a coral’s white skeleton can be seen through its translucent flesh, giving off a bleached appearance.
Mass coral bleaching over large areas, first noticed in the 1980s around the Caribbean, is caused by rising ocean temperatures.
Some corals also display fluorescent colours under stress when they release a pigment that filters light. Sunlight also plays a role in triggering bleaching.
Corals can survive bleaching if temperatures are not too extreme or prolonged. But extreme marine heatwaves can kill corals outright.
Coral bleaching can also have sub-lethal effects, including increased susceptibility to disease and reduced rates of growth and reproduction.
Scientists say the gaps between bleaching events are becoming too short to allow reefs to recover.
Coral reefs are considered one of the planet’s ecosystems most at risk from global heating. Reefs support fisheries that feed hundreds of millions of people, as well as supporting major tourism industries.
The world’s biggest coral reef system – Australia’s Great Barrier Reef – has suffered seven mass bleaching events since 1998, of which five were in the past decade.
The previous back-to-back bleaching on the Great Barrier Reef happened in the summers of 2016 and 2017.
Last year’s bleaching was the most widespread on record. Subsequent surveys in the months afterwards found record annual losses in coral cover in several areas.
The Albanese government has previously budgeted $1.2bn for reef conservation until 2030, but there was no new money in the most recent budget earmarked for its recovery. Last week Labor pledged an extra $10m for reef eduction projects.
So far, the reef’s decline has not been one of the election’s topical issues discussed in detail by either the prime minister or Peter Dutton, whose home state is Queensland.
The authority said there was also evidence that flooding from record rainfall in Queensland during the summer had damaged corals on reefs close to shore in the central and northern areas.
“It will take time to fully understand the extent and implications of these compounding climate-driven events,” the authority said.
Australia’s other World Heritage-listed reef on the Ningaloo coast in Western Australia has also been hit by extreme levels of bleaching and heat stress since February.
after newsletter promotion
A study last year found temperatures over the Great Barrier Reef were now at their hottest in at least 400 years.
Bleaching at Ningaloo and the Great Barrier Reef has been part of the ongoing fourth global mass bleaching event that has hit 83% of the planets coral reefs across at least 82 countries and territories between 1 January 2023 and 10 April, according to US government data.
Prof Morgan Pratchett, a coral reef expert at James Cook University in Townsville, said: “Bleaching is prevalent now nearly every year. People are just not impacted by it as they used to be because it’s become the new normal and it doesn’t resonate the way it used to.
“The biggest cause of coral mortality is climate change. From a triage perspective, that’s where we have to start. These impacts will keep getting worse until we do something serious about it.”
The head of oceans at WWF Australia, Richard Leck, said the reef was “crying out for climate action”.
“Coral bleaching is becoming the new normal,” he said. “Year after year the reef is being cooked by underwater heatwaves. The next term of government could be the last opportunity to give the reef a fighting chance.”
Simon Miller, reef campaigner at the Australian Marine Conservation Society, said the reef was still trying to recover from last year’s mass bleaching event.
“These reports continue to show the damage climate change is causing, but they must lead to action. Monitoring is essential, but it cannot be where our response ends. Australia must rapidly slash climate pollution and stop new fossil fuel approvals.”
“The number one thing the Australian and Queensland governments must do is adopt reef-safe climate policies.
“That means cutting climate pollution by 90% by 2035 and stopping approvals for new fossil fuel projects. Without tackling the root cause of the problem, the reef’s long-term health and resilience are seriously jeopardised.”
