Bleached coral is visible at the Flower Garden Banks National Marine Sanctuary, off the coast of Galveston, Texas, in the Gulf of Mexico, September 16, 2023. Ocean temperatures that have gone “crazy haywire” hot, especially in the Atlantic, are close to making the current global coral bleaching event the worst in history. It’s so bad that scientists are hoping for a few hurricanes to cool things off.
| Photo Credit: AP

Nearly two-thirds of the world’s coral reefs have been subjected to heat stress bad enough to trigger bleaching over the past year, the leading agency monitoring coral reefs said on Thursday.

The U.S. National Oceanic and Atmospheric Administration (NOAA) announced last month that the world’s coral reefs were in the throes of a fourth mass bleaching event, as climate change combined with an El Nino climate pattern has pushed ocean temperatures to record highs.

Now, the agency reports some 60.5% of the world’s reef area has been affected and that number is still rising.

“I am very worried about the state of the world’s coral reefs,” NOAA’s Coral Reef Watch coordinator Derek Manzello said in a monthly briefing. “We are seeing (ocean temperatures) play out right now that are very extreme in nature”.

Triggered by heat stress, coral bleaching occurs when corals expel the colourful algae living in their tissues. Without these helpful algae, the corals become pale and are vulnerable to starvation and disease.

Scientists have documented mass bleaching in at least 62 countries and territories, with India and Sri Lanka recently reporting impacts.

The last global event, which ran from 2014 to 2017, saw 56.1% of reef areas subjected to bleaching-level heat stress. Previous events in 1998 and 2010 hit 20% and 35% of reef area, respectively.

While the current event has affected a greater swath, Manzello said the 2014-17 event is still considered the worst on record due its severity and persistence. But 2023-24 could soon surpass it, he added.

Caribbean corals at risk

Corals in the Atlantic Ocean have been hit hardest by soaring ocean temperatures, with 99.7% of the basin’s reefs subjected to bleaching-level heat stress in the past year, NOAA said.

“The Atlantic Ocean has been off the charts,” Manzello said.

One assessment published in April 2024 found there had so far been between 50% and 93% coral mortality at Huatulco, Oaxaca, in the Mexican Pacific.

The situation is likely to worsen this summer, as heat stress is once again accumulating in the Southern Caribbean. In some areas, the heat stress threshold for bleaching to occur has already been passed.

“This is alarming because this has never happened so early in the year before,” Manzello said.

Scientists are expecting further bleaching in the Southern Caribbean, around Florida, and at the Mesoamerican Barrier Reef – the world’s second largest reef – this summer.

“El Nino is dissipating, but the ocean is still anomalously hot. It won’t take much additional warming to push temperatures past the bleaching threshold,” he said.

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.”