It's an Unwelcome First for Australia's 2 Biggest Reefs

Two-thirds of the Great Barrier Reef has seen its sharpest annual decline in coral cover since records began 40 years ago, with scientists warning this iconic ecosystem may be nearing a tipping point, per the Guardian. The latest survey from the Australian Institute of Marine Science (AIMS)—covering 124 reefs between August 2024 and May 2025, encompassing a mass bleaching event—points to extensive coral bleaching in both the northern and southern sections of the Great Barrier Reef, per the BBC. This marks the most widespread bleaching on record for the reef, which stretches some 1,500 miles along Australia's coast.

AIMS attributes the ongoing coral decline primarily to heat stress linked to climate change, although recent tropical cyclones and outbreaks of coral-eating crown-of-thorns starfish have also contributed. The report warns that the reef may be reaching a point where it can't recover quickly enough between damaging events, leaving its future increasingly unstable.

This year, both the Great Barrier Reef and Ningaloo Reef on Australia's west coast experienced simultaneous mass bleaching for the first time. Bleaching occurs when corals are stressed by warmer water, causing them to lose color and, if high temperatures persist, die. Acropora corals—fast growing but particularly vulnerable—were hit hardest. AIMS notes that coral can recover if given several undisturbed years, but repeated stress makes this less likely. The report credited Australia's crown-of-thorns starfish culling program with reducing outbreaks in the central reef, but long-term threats remain.