The Australian Institute of Marine Science released its latest long-term monitoring summary overnight, recording the largest single-year drop in coral cover since the program began 39 years ago. Surveys of 124 reefs between August 2024 and May 2025 found that hard-coral cover fell by 30 percent in the southern Great Barrier Reef, 25 percent in the north, and 13.9 percent in the central region. Two reefs now hold less than 10 percent cover, and average coral cover across the reef returned to near the long-term mean after several years of growth.
“The results from this year really underscore the amount of stress the Great Barrier Reef is under,” said Mike Emslie, leader of the Institute’s Long-Term Monitoring Program. “The number one cause is climate change. There is no doubt about that,” he added. Selina Stead, the Institute’s chief executive, called the 2024 bleaching “the largest spatial footprint recorded, with high to extreme bleaching prevalence across all three regions of the Great Barrier Reef”.
Bleaching occurred when water temperature rose and corals expelled the zooxanthellae algae that fed them. Without the algae, coral tissue became transparent, exposing the white skeleton and leaving colonies open to starvation and disease. A 2024 marine heatwave imposed unprecedented thermal stress, and the Australian National University reported the highest average sea-surface temperatures ever recorded around the continent that year. Above-average heat turned banks of Acropora—the reef’s fast-growing but heat-sensitive corals—white. “We’ve said in the past that these corals are the fastest to grow and are the first to go,” Emslie noted.
Average coral cover in the northern sector declined from 39.8 to 30 percent, in the south from 38.9 to 26.9 percent, and in the central region from 33.2 to 28.6 percent. Seventy-seven reefs now sit between 10 and 30 percent cover, thirty-three between 30 and 50 percent, ten between 50 and 75 percent, and only two above 75 percent. Individual losses reached 70 percent near Lizard Island. One component of the monitoring program towed an observer around each reef’s perimeter to record live, bleached and dead coral, creating the most extensive record of its kind on any reef ecosystem.
Tropical cyclones and outbreaks of crown-of-thorns starfish continued to erode coral in the north and south. The starfish, an invasive predator that can grow to 80 centimeters and bears up to 21 toxin-tipped arms, favored Acropora and increased in number since the 1960s. Over the past year the federal control program injected more than 50,000 starfish with vinegar or ox bile, but outbreaks persisted, fueled by nutrient-rich runoff that fed starfish larvae.
The latest losses occurred during a global mass-bleaching episode that over the past two years affected more than 80 percent of the world’s reefs. The Great Barrier Reef endured six such events in nine years and five since 2016. “We see that coral cover oscillates between record highs and lows within a relatively short time,” said Emslie.
Despite the damage, the reef still held more coral than many other systems, and its biodiversity remained exceptional: more than 600 coral species, 1,625 fish species and 4,000 mollusk species inhabit the 2,400-kilometre-long structure of roughly 3,000 reefs and 900 islands. It contributed A$6.4 billion to the national economy each year and remained a popular diving destination. UNESCO recommended listing it as a world-heritage site in danger, a step successive Australian governments lobbied to avoid out of concern for tourism.
Australia is preparing the next cycle of emissions-reduction targets under the Paris Agreement, yet the country remains one of the world’s largest coal exporters and subsidizes fossil-fuel industries. “The future of the world’s coral reefs relies on strong greenhouse-gas emissions reduction, management of local and regional pressures, and development of approaches to help reefs adapt to and recover,” said Stead. Richard Leck of WWF warned, “It’s the sign of an ecosystem under incredible pressure, and what concerns reef scientists enormously is when the reef doesn’t recover as it used to”.
AIMS cautioned that the time between bleaching events is shrinking, leaving corals too little respite. Scientists estimated the reef would need 10 to 15 years to recover from the latest bleaching—if it recovers at all—and only under minimal future disturbance. “It is still worth fighting for; we cannot give up and abandon it,” said Emslie.
Written with the help of a news-analysis system.