Coral has been reduced to rubble in parts of the Great Barrier Reef after a marine heatwave caused "catastrophic" damage off Queensland's coast.
Western Australia is also feeling the impact of rising ocean temperatures, with thousands of fish dying and coral bleaching intensifying across the Kimberley region.
Scientists studied the health of 462 coral colonies near One Tree Island in the southern Great Barrier Reef off Queensland's coast during a heatwave in 2024.
The marine heatwave was the seventh mass bleaching event on the reef since 1998 and the fifth since 2016.
It brought severe conditions and rapid coral health decline not previously seen in the southern reef region.
"What we saw at One Tree Reef was catastrophic," said Michael Kingsford, Distinguished Professor of Marine Biology at James Cook University.
"Rapid high mortality left no opportunity for these corals to recover, some coral even turned to rubble."
Coral bleaching is a stress response caused by changes to the environment such as increased water temperatures or freshwater flooding.
Coral has single-celled algae called zooxanthellae living inside it which gives it colour and food.
But when the coral gets stressed it expels the algae and turns white.
Scientists found that the heatwave bleached two-thirds of the coral colonies by February 2024 which rose to more than three-quarters by April.
Nearly half of the colonies were dead by May, growing to 53 per cent in July.
The study revealed 31 per cent of the coral colonies remained bleached while 16 per cent recovered.
Prof Kingsford said mass bleaching events were becoming more common on the reef, occurring every two years.
The dire situation sparked a renewed call for action on global warming to prevent the Australian icon from being destroyed.
"Catastrophic conditions and dire ecosystem changes are no longer a threat on a distant horizon," he said.
"It’s happening now.
"Our findings reinforce the need for urgent global action, immediately, on ambitious climate and reduced emissions target."
The study was published in the Association for the Sciences of Limnology and Oceanography.
It's not just the Great Barrier Reef experiencing the detrimental impacts of marine heatwaves.
WA's Department of Primary Industries and Regional Development has linked more than 30,000 dead fish washing up on Gnoorea Beach in recent weeks to an extreme category three marine heatwave.
Scientists expect the heatwave to worsen in the coming months.
Coral bleaching has been occurring across the reefs near Broome, Entrance Point and Coconut Wells since Christmas due to ocean temperatures reaching up to five degrees above normal.
“Kimberley corals are known to be the most robust in the world and can withstand temperature ranges much more than corals elsewhere," said Martin Pritchard, Environs Kimberley Executive Director.
"But fragile ecosystems like the remote and precious Scott Reef are now at risk."
