Great Barrier Reef Suffers Worst Coral Decline on Record

Parts of the Great Barrier Reef have suffered the largest annual decline in coral cover since records began nearly 40 years ago, according to a new report.

The Great Barrier Reef stretches 2,300 km (1,429 miles) and houses an extraordinary array of biodiversity.

The northern and southern branches of the sprawling Australian reef both experienced their most widespread coral bleaching, the Australian Institute of Marine Science (AIMS) found, Tom McArthur reported for BBC News.

Reefs have been battered in recent months by tropical cyclones and outbreaks of crown-of-thorns starfish that feast on coral, but heat stress driven by climate change is the predominant cause, AIMS said.

The institute warns the habitat may be reaching a tipping point where coral cannot recover fast enough between catastrophic events, facing a “volatile” future.

AIMS surveyed the health of 124 coral reefs between August 2024 and May 2025, continuing a monitoring effort it began in 1986.

Often dubbed the world’s largest living structure, the Great Barrier Reef stretches 2,300 km (1,429 miles) and houses an extraordinary array of biodiversity. Repeated bleaching events are turning vast swaths of once-vibrant coral white.

Australia’s second-largest reef, Ningaloo — on the country’s western coast — has also experienced repeated bleaching, and this year both major reefs turned white simultaneously for the first time ever.

Coral, often called the sea’s architect, is vital to the planet, building vast structures that house an estimated 25% of all marine species. Bleaching occurs when coral becomes stressed — typically due to excessively warm water — and expels the algae that give it color, turning it white.