Warming oceans caused Great Barrier Reef to experience largest die-off in decades

The UNESCO-listed Great Barrier Reef has suffered its most extensive annual loss of living coral in four decades of records, according to Australian authorities.

Despite this, thanks to significant coral growth between 2017 and 2023, the widespread die-off, which is mainly caused by climate change-driven bleaching last year, has left the reef's overall coral coverage close to its historical average, the Australian Institute of Marine Science (AIMS) said in its August 6 report, as cited by AP.

Still, the findings highlight a growing unpredictability within the World Heritage Site, the report warned. Mike Emslie, who leads the long-term monitoring program at AIMS, said that although coral losses were high, they followed a peak year. The amount of live coral measured in 2024 was the highest seen in nearly four decades of surveys.

The large starting base of coral had helped buffer the reef from the full force of the latest environmental stress, said Emslie. The Great Barrier Reef stretches across 344,000 square kilometres off the northeastern coast of Australia, making it the world’s largest coral reef ecosystem.

“These are major impacts, and they’re proof that the increased frequency of bleaching events is beginning to take a real toll on the Great Barrier Reef,” Emslie said in a statement following the report.

“There is still a lot of coral out there, but the magnitude of these declines in a single year is unprecedented in the history of our monitoring,” he added.

According to the report, live coral cover declined by nearly one-third in the southern section of the reef, by a quarter in the northern region, and by 14% in the central area in just one year.

Amid record global heat in 2023 and 2024, the world is enduring its largest and fourth-ever mass coral bleaching event. Nearly 84% of global coral reef systems, including the Great Barrier Reef, have been affected by heat stress, according to NOAA’s Coral Reef Watch program. So far, at least 83 nations have reported impacts.

Coral reefs are highly sensitive to sustained heat. While they can handle brief warming, prolonged exposure to high temperatures causes coral bleaching—when corals expel the algae living in their tissues that give them colour and nourishment. Bleached coral isn't immediately dead, but it becomes fragile and susceptible to disease.

The current bleaching event began in January 2023 and was officially declared a global crisis in April 2024. It has already surpassed the previous record bleaching event between 2014 and 2017, when 68.2% of global reefs were affected by thermal stress.

By Nazrin Sadigova