“Much of the recent hard-cover increase was driven by increases in the fast-growing Acropora corals, which have proliferated across many Great Barrier Reef reefs,” AIMS said of its survey results.

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The Acropora genus includes table and staghorn branching corals. Many other corals, like the massive boulder corals of the Porites genus, take decades to regrow.

The ARC Centre of Excellence for Coral Reef Studies has found that the number of corals across the Great Barrier Reef had halved in the past 20 years, and the reduction in coverage and diversity of corals had shrunk crucial habitat for species that comprised the reef’s vibrant marine life.

It also said mass coral bleaching had “cascading effects on community composition and ecosystem functioning”. In other words, the nature of the ecosystem could be turned on its head.

Australia’s climate has already warmed by an average of 1.47 degrees over the past century, and sea surface temperatures have increased by an average of 1.05 degrees.

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AIMS survey leader Dr Mike Emslie said bleaching was the greatest risk to the reef and reducing greenhouse emissions was the best way to protect it.

“We’re already seeing biennial bleaching events. If we keep pushing through that 1.5 [degrees] envelope, the predictions are these bleaching events are going to become a lot more frequent than that and there’s only so much resilience inherent in the system.”

AIMS research director Dr David Wachenfeld said the strong regrowth figures could already have been undone by last summer’s bleaching event.

“We are only one large-scale disturbance event away from a reversal of the recent recovery. The 2024 bleaching event could be that event – almost half of the 3000 or so reefs that make up the marine park experienced more heat stress than ever recorded,” Wachenfeld said.

Bleaching occurs when corals are put under severe stress due to high water temperatures, which causes the organisms to expel the algae living in their tissues and turn white.

Not all corals that turn white die. They can recover if sea surface temperatures return to normal quickly enough.

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