Subscribe
Three-quarters of Goniopora corals at One Tree Reef have died after bleaching and black band disease.
The losses occurred during the fourth global mass bleaching event, affecting 84% of reefs worldwide.
Extreme heat weakened corals, enabling rapid, unprecedented spread of the disease.
Goniopora are usually thermally tolerant, making the event a major warning for global reef resilience.
Scientists say accelerating climate change is outpacing corals’ ability to recover and survive.
A combination of extreme heat stress and a rare coral disease has wiped out 75 per cent of Goniopora colonies at a site on the Great Barrier Reef, scientists have reported, raising fresh alarms over the accelerating impacts of climate change on coral ecosystems.
The findings come as the world experiences its fourth global mass bleaching event, with nearly 84 per cent of coral reefs worldwide now affected — the worst and most extensive bleaching on record.
Researchers inspecting 112 colonies at One Tree Reef (OTR), off Queensland, found that severe bleaching triggered by extreme ocean temperatures was followed by an unprecedented outbreak of black band disease (BBD), a rare but aggressive bacterial infection that kills coral tissue as it spreads across a colony.
The study, published in the journal Proceedings of the Royal Society B on December 10, 2025, reports that OTR has not seen bleaching of this severity for decades. The large, long-lived Goniopora, also known as flowerpot or daisy corals typically inhabit lagoons and turbid reefs and are considered thermally tolerant, making the scale of mortality especially alarming.
“Increased temperature is also linked to outbreaks of coral disease. Other adverse environmental stressors, especially high light levels and decreased salinity, also cause bleaching,” the authors noted.
Scientists said bleached corals were left in a weakened state, making them highly susceptible to disease, while warm conditions increased the virulence of pathogens. Although corals can recover once temperatures fall, their compromised health leaves them vulnerable to infection.
“While the relationship between coral bleaching and disease is not clear, the strong relationship between heat stress and disease outbreaks emphasises the increased risk of coral disease due to climate change,” it said.
Black band disease, common in the Caribbean but historically rare in the southern Great Barrier Reef, appeared in a few colonies in February 2024. By April, 61 per cent of bleached colonies were infected, and the disease spread in an epizootic-like manner, the authors noted.
Population surveys of more than 700 Goniopora colonies revealed the same pattern: widespread bleaching, rapid disease progression and high mortality. The disease occurred only on corals that had bleached.
Temperatures at OTR between December 2023 and February 2025 were extreme, with mean, minimum and maximum daily temperatures above 28 degrees Celsius (°C), 29°C and 30°C respectively. During the bleaching event, water temperatures exceeded 28°C for 74 consecutive days. Temperatures were above 29°C for 21 days in January-February 2024, and peaked at 34-35°C during the year.
Researchers noted that while BBD is often associated with pollution and nutrient loading, OTR’s offshore location means it is largely sheltered from such coastal stressors. Although the lagoon can experience slightly elevated nutrient levels, Goniopora corals are typically found on turbid inshore reefs, making this an unlikely trigger.
“Rather than recovering from bleaching as the water cooled, as might be expected if temperature was the main stressor, survival plummeted. Clearly, BBD was a major driver of mortality as the aggressive black band invaded the tissue,” the scientists concluded.
Surveys in the northern Great Barrier Reef during 2024 recorded very low BBD incidence, affecting only 1-2 per cent of Acropora and Montipora corals, with no coincident bleaching.
“The question arises as to why this relatively rare coral disease appeared in the Goniopora colonies at OTR. No other coral genera that bleached in the 2024 event at OTR developed the disease,” researchers wrote.
The authors warned that the event underscores the accelerating risks to coral reefs as climate change intensifies.
“The current trajectory of climate change is progressing too quickly for corals to adjust,” they said. “Coral reefs are in danger, with recurrent anomalous heatwaves and mass bleaching being the greatest threat to their survival.”
Maria Byrne, professor of marine biology in the School of Life and Environmental Sciences at the University of Sydney, said the loss of these large, structure-forming corals would have long-term repercussions on reef biodiversity, coastal protection and food security.
“Coral reefs support more than a billion people worldwide. What we’re witnessing is a collapse in the natural resilience of these ecosystems. Ambitious global action to reduce emissions is now the only path to their survival,” she said.