Recent mass bleaching, two cyclones, and flooding have left large portions of Australia’s Great Barrier Reef with “significant coral mortality,” new data from the Australian Institute of Marine Science (AIMS) has revealed.
Between August and October, researchers conducted in-water surveys of 19 reefs stretching from Lizard Island to Cardwell, finding up to 72% coral mortality on 12 of the reefs surveyed. In a northern section of the reef, from Cooktown to Lizard Island, scientists recorded a loss of over a third of hard coral cover—marking the “largest annual decline” in coral health since government monitoring began 39 years ago, according to AIMS.
AIMS scientists attributed this extensive damage to the Austral summer, Tropical Cyclones Jasper and Kirrily, and intense freshwater flooding between December 2023 and March 2024. Currently, researchers are continuing to gather data from reefs in the southern region of the Great Barrier Reef.
“These initial results show the vulnerability of the Reef to bleaching events, which are increasing in frequency, footprint, and intensity under climate change. Its resilience is being severely tested,” said AIMS Acting Research Programme Director, Manuel Gonzalez Rivero.
The Great Barrier Reef spans roughly 2,300 kilometres (1,429 miles) off Australia’s northeastern coast and is among the world’s most species-rich habitats, hosting hundreds of coral species, over 1,600 fish species, 133 types of sharks and rays, and 30 species of whales and dolphins. However, frequent mass bleaching has diminished its vibrant colours, turning coral beds white.
Bleaching occurs when rising water temperatures stress coral, causing it to expel microscopic algae, or zooxanthellae. Prolonged heat stress can leave corals unable to recover, resulting in death.
The current year has already been confirmed as the fifth mass bleaching event in just eight years. Survey data also showed the highest death rate among a rapidly growing coral species, Acropora, known to be particularly vulnerable to bleaching due to its fast growth.
Lead researcher Mike Emslie described the past summer as “one of the most severe events” across the Great Barrier Reef, with heat stress surpassing previous records. “These are serious impacts. These are serious losses,” he told Australia’s ABC.
Bleaching and bleak future of reefs
Richard Leck, head of oceans for WWF-Australia, said the initial survey results confirmed his “worst fears” for the reef’s future.
“The Great Barrier Reef can bounce back, but there are limits to its resilience. It can’t get repeatedly hammered like this. We are fast approaching a tipping point,” Leck warned.
He added that while the area surveyed was “relatively small,” he feared similar levels of coral mortality would be found across other parts of the reef when the full report is released next year. Leck urged Australia to commit to stronger emission reduction targets, aiming for a minimum 90% cut from 2005 levels by 2035, and to shift away from fossil fuel dependency.
Australia, one of the world’s top exporters of gas and coal, has recently begun taking steps toward carbon neutrality, but Leck argues that more ambitious action is necessary to safeguard the future of the reef.
