Great Barrier Reef suffers record coral loss after years of growth

The Great Barrier Reef has just faced its largest single-year loss of live coral since surveys began nearly four decades ago. Australian authorities say the losses were driven mostly by a major bleaching event last year linked to climate change.

Still, despite the heavy toll, overall coral cover remains close to the long-term average. That’s because coral growth in recent years – especially since 2017 – had boosted the reef’s health before this latest setback.

Increasing frequency of coral bleaching

Scientists from the Australian Institute of Marine Science report that 2024’s live coral cover was the highest recorded in 39 years of surveys, and this made the recent losses all the more striking.

Mike Emslie, who heads the institute’s long-term monitoring program, explained that starting from a strong base meant the reef was somewhat cushioned against the worst effects of climate damage. But that cushion is shrinking.

“These are substantial impacts and evidence that the increasing frequency of coral bleaching is really starting to have detrimental effects on the Great Barrier Reef,” Emslie said. “While there’s still a lot of coral cover out there, these are record declines that we have seen in any one year of monitoring.”

Coral loss on the Great Barrier Reef

The reef stretches 1,500 kilometers (900 miles) along the Queensland coast and is divided into three main regions: north, central, and south.

According to the survey, the south lost nearly a third of its living coral in just 12 months, the north lost about a quarter, and the central region experienced a 14% decline.

The Great Barrier Reef’s struggles are part of a much wider problem. Since early 2023, the world has been in the grip of its largest recorded mass coral bleaching event.

It’s only the fourth such global crisis ever documented, but it has already affected nearly 84% of the planet’s coral reef areas, according to the U.S. National Oceanic and Atmospheric Administration’s Coral Reef Watch.

This event, which began in January 2023 and was declared a crisis in April 2024, has surpassed the previous worst bleaching period from 2014 to 2017, when 68.2% of reefs were affected.

In Australia, aerial surveys of 281 reefs in the Torres Strait and northern Great Barrier Reef confirmed widespread bleaching. Of those, 78 reefs had more than 30% of their coral bleached.

Why heat hurts coral

Coral can cope with short bursts of warm water, the kind that might pass after a few days. But when the heat lingers for weeks, it’s a different story.

The coral gets stressed and pushes out the tiny algae living inside its tissues. These algae are more than just tenants – they give coral its color and, more importantly, most of its food.

Without them, the coral turns ghostly white in a process known as “bleaching.” Bleached coral isn’t necessarily dead right away, but it’s weakened. It’s like losing your main source of food – you can survive for a while, but your strength fades, and you’re more likely to get sick.

Frequent coral bleaching events

If the water cools down soon enough, the algae can return and the coral can recover. But when the heat stays for too long, the coral can starve and die. Even when coral survives, it tends to regrow more slowly and becomes less resilient to future stress.

What makes today’s bleaching events so alarming is how often they’re happening. In the past, a reef might have had a decade to bounce back between big bleaching events.

Now, the gap can be just a few years – not nearly enough time for full recovery. And each time it happens, the reef loses a little more of its strength.

A fragile future for coral reefs

The United Nations Intergovernmental Panel on Climate Change warns that tropical coral reefs are among the most vulnerable ecosystems to rising temperatures.

In 2018, the panel said they face “very high risk” at just 1.5°C of global warming, with most evidence suggesting they could largely disappear beyond that threshold.

The world has already warmed 1.3°C since pre-industrial times. And past back-to-back bleaching events on the Great Barrier Reef suggest that scientists may have underestimated the risks.

“Warm water (tropical) coral reefs are projected to reach a very high risk of impact at 1.2°C, with most available evidence suggesting that coral-dominated ecosystems will be non-existent at this temperature or higher. At this point, coral abundance will be near zero at many locations,” the researchers concluded.

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