A marine heatwave followed by an outbreak of a tissue-killing disease rarely seen in the Great Barrier Reef has taken out typically heat-resilient coral varieties.
Marine scientists said the combination of record heat and infection was "catastrophic" for the One Tree Reef area studied and suggested tropical corals were struggling to withstand coalescing pressures.
Goniopora, otherwise known as flowerpot or daisy corals, were long-lived corals that typically bounced back after bleaching events caused by heat stress.
Monitoring of corals at the southeast end of the World Heritage-listed reef following the unprecedented marine heatwaves of 2024, fuelled by an El Nino and global warming, found 75% of the heat-resilient Goniopora colonies had bleached.
The corals were then struck by black band disease – more common in the Caribbean but unusual in Australian waters – which spread aggressively to infect half the bleached colonies by April.
Three-quarters of the resilient coral colonies had died by October and only a quarter showed a partial recovery
The bacterial necrotic infection formed a black band that crossed the infected coral and usually killed invaded colonies.
It was often linked to pollution or nutrient run off.
Queensland was a known hotspot for deforestation and landclearing in catchments that flowed into the Great Barrier Reef causing erosion that washed debris into waterways, sending sediment, nutrients and pesticides downstream and into the ocean.
Study leads Professor Maria Byrne and Dr Shawna Foo said the findings suggested climate change was happening too quickly for corals to adjust.
"Normally these massive corals withstand environmental stress, but the combination of record heat and infection was catastrophic," said Foo, a lecturer at the university's School of Life and Environmental Sciences.
Byrne said the devastation of reef-forming structural corals would devastate biodiversity, coastal protection and food security.
"Coral reefs support more than a billion people worldwide," the professor of marine biology said.
"Ambitious global action to reduce emissions is now the only path to their survival."
A report prepared by 160 researchers worldwide ahead of this year's COP30 climate summit suggested the world's tropical reefs were the first climate-driven ecosystem to pass a "tipping point" of irreversible decline.
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