The Great Barrier Reef has experienced its greatest annual loss of live coral across most of its expanse in four decades of record-keeping, Australian authorities say.

Also Read | Australia’s Great Barrier Reef off UNESCO danger list, still under ‘serious threat’

But due to increasing coral cover since 2017, the coral deaths — caused mainly by bleaching last year associated with climate change — have left the area of living coral across the iconic reef system close to its long-term average, the Australian Institute of Marine Science said in its annual survey on Wednesday (August 6, 2025).

The change underscores a new level of volatility on the UNESCO World Heritage Site, the report said.

Mike Emslie, who heads the tropical marine research agency’s long-term monitoring program, said the live coral cover measured in 2024 was the largest recorded in 39 years of surveys.

The losses from such a high base of coral cover had partially cushioned the serious climate impacts on the world’s largest reef ecosystem, which covers 344,000 square kilometers (133,000 square miles) off the northeast Australian coast, he said.

“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 on Thursday.

“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,” he added.

Mr. Emslie’s agency divides the Great Barrier Reef, which extends 1,500 kilometres (900 miles) along the Queensland state coast, into three similarly-sized regions: northern, central and southern.

Living coral cover shrunk by almost a third in the south in a year, a quarter in the north and by 14% in the central region, the report said.

Because of record global heat in 2023 and 2024, the world is still going through its biggest — and fourth ever recorded — mass coral bleaching event on record, with heat stress hurting nearly 84% of the world’s coral reef area, including the Great Barrier Reef, according to the U.S. National Oceanic and Atmospheric Administration’s coral reef watch. So far at least 83 countries have been impacted.

This bleaching event started in January 2023 and was declared a global crisis in April 2024. It easily eclipsed the previous biggest global coral bleaching event, from 2014 to 2017, when 68.2% had bleaching from heat stress.

Large areas around Australia — but not the Great Barrier Reef — hit the maximum or near maximum of bleaching alert status during this latest event. Australia in March this year started aerial surveys of 281 reefs across the Torres Strait and the entire northern Great Barrier Reef and found widespread coral bleaching. Of the 281 reefs, 78 were more than 30% bleached.

Coral has a hard time thriving and at times even surviving in prolonged hot water. They can survive short bursts, but once certain thresholds of weeks and high temperatures are passed, the coral is bleached, which means it turns white because it expels the algae that live in the tissue and give them their colors. Bleached corals are not dead, but they are weaker and more vulnerable to disease.

Coral reefs often bounce back from these mass global bleaching events, but often they are not as strong as they were before.

Coral reefs are considered a “unique and threatened system” due to climate change and are especially vulnerable to global warming beyond 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times, the United Nations Intergovernmental Panel on Climate Change proclaimed in 2018. The world has now warmed 1.3 degrees Celsius since pre-industrial times. That report said “tropical corals may be even more vulnerable to climate change than indicated in assessments made in 2014.”

The report said back-to-back big bleaching events at the Great Barrier Reef in the mid 2010s “suggest that the research community may have underestimated climate risks for coral reefs.”

“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 report said.

Published – August 07, 2025 10:23 am IST

Australia’s famed Great Barrier Reef is suffering one of the most severe coral bleaching events on record, leaving scientists fearful for its survival as the impact of climate change worsens.

For 33 years marine biologist Anne Hoggett has lived and worked on Lizard Island, a small slice of tropical paradise off Australia’s northeast tip.

She affectionally dubs it “Blizzard Island”. The only relief from the wind and teeming showers is in the powder blue waters, where sea turtles and tiger sharks rove along the Great Barrier Reef.

As Hoggett snorkels, schools of fish swim gracefully, feeding on the coral or darting between it. Some are as small as her little finger, others the colour of fire.

But thanks to climate change, it is becoming a watery graveyard of bleached reef.

“We don’t know yet if they’ve already sustained too much damage to recover or not,” said Hoggett.

The world is currently experiencing its second major coral bleaching event in 10 years, the US National Oceanic and Atmospheric Administration (NOAA) announced Monday.

Coral bleaching occurs when water temperatures rise more than one degree Celsius (33.8 degrees Fahrenheit).

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” said NOAA’s Derek Manzello.

In a bid to survive, the coral expels microscopic algae, known as zooxanthellae, which it needs to live.

If high temperatures persist, the coral eventually evicts most of the zooxanthellae, turns white, and dies.

Since February, ocean temperatures around Lizard Island have been up to two degrees Celsius warmer than the average.

Hoggett estimates about 80% of the coral is already dead.

Just about everything died

Often dubbed the world’s largest living structure, the Great Barrier Reef is a 2,300-kilometre (1,400-mile) long expanse housing a stunning array of biodiversity, including more than 600 types of coral and 1,625 fish species.

It is vital to the health of the ocean and Australia’s tourism industry, netting billions of dollars every year.

But repeated mass bleaching events have robbed the reef of its wonder, turning banks of once-vibrant corals to a sickly ashen white.

In March, Australian reef authorities announced another mass bleaching event was underway, the fifth in eight years.

Through aerial monitoring, they found more than 600 reefs have experienced bleaching.

Ten per cent of the area is classed as suffering extreme bleaching, when more than 90% of corals are distressed and unlikely to survive.

Just nine weeks ago, the reef off Lizard Island was healthy and vibrant, Hoggett said.

Now, she points to the fluorescent pink and blue coral. Despite its initial beauty, that means the coral is highly stressed and expelling the healthy algae it needs to survive.

Elsewhere, white coral is covered in a fluffy, brown algae — a sign it is dead.

When Hoggett first arrived on the island three decades ago, bleaching would occur every 10 years or so. Now, it is happening every year.

Mass bleaching events along the reef occurred in 1998, 2002, 2016, 2017, 2020, 2022 and now 2024.

She is heartbroken.

“The only time we’ve seen bleaching this bad was in 2016, when just about everything died,” Hoggett told AFP.

“It’s anybody’s guess as to how many of these corals that are still alive now will be able to survive and recover.”

Too small in scale

While reefs can recover from bleaching, the window of recovery between events is narrowing.

As the planet continues to warm, bleaching is forecast to reduce global coral cover by 95% if temperatures warm by about two degrees.

If the rise is up to 1.5 degrees above pre-industrial levels, bleaching will spread to 70%.

Even if all countries deliver on their climate commitments, the world would still be on track for two degrees or more of warming.

Globally, billions of dollars are being poured into coral bleaching mitigation projects — including breeding coral on artificial reefs and translocating it, making clouds more heat reflective, or controlling coral predators.

These site-specific conservation efforts are important, but Terry Hughes, one of Australia’s foremost coral reef scientists, says they do nothing to address the root cause of bleaching: climate change.

“After 50 years of interventions, coral restoration attempts have not changed the ecology of a single reef anywhere,” Hughes said. “They’re just too small in scale.”

For example, Hughes says breeding corals in aquariums has strict limitations.

“You would need 250 million large corals, each the size of a dinner plate, to increase coral cover in the Great Barrier Reef by just one per cent — and it would cost billions of dollars,” he added.

“The solution is to reduce greenhouse gas emissions as quickly as possible.”

Not giving up

Australia has invested about Aus$5 billion ($3.2 billion) into improving water quality, reducing the effects of climate change, and protecting threatened species.

The country is one of the world’s largest gas and coal exporters, and has only recently set loose targets to become carbon neutral.

Whether these efforts will be enough to see the reef keep its World Heritage Status will be examined by UNESCO later this year.

Great Barrier Reef Marine Park Authority chief scientist Roger Beeden says it will take some time before the full extent of this year’s event are realised, but he is hopeful coral will recover.

“There’s hundreds of species of corals, they have evolved in an environment that is incredibly dynamic. They are very adaptable,” he said.

“We need to do all that we can. I’m always hopeful. I think like medical doctors — I’m not giving up on this patient.”

On Lizard Island, Hoggett worries for its future.

“Coral reefs are so beautiful, and I love them so much. They do so much good for the world,” she said.

“It just makes me angry that it’s within our power to stop this from happening and we are not doing anything quickly enough.”