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.

An undated photo received from ARC Centre of Excellence for Coral Reef Studies shows a ‘mass bleaching event’ of coral on Australia’s Great Barrier Reef. File
| Photo Credit: AFP

A “mass bleaching event” is unfolding on Australia’s famed Great Barrier Reef, authorities said on March 8, as warming seas threaten the spectacular home to thousands of marine species.

Often dubbed as the world’s largest living structure, the Great Barrier Reef is a 2,300 km (1,400 mile) expanse of tropical corals that house a stunning array of biodiversity.

But repeated mass bleaching events have threatened to rob the tourist drawcard of its wonder, turning banks of once-vibrant corals into a sickly shade of white.

“We know the biggest threat to coral reefs worldwide is climate change. The Great Barrier Reef is no exception,” Environment Minister Tanya Plibersek said in a statement.

“We need to act on climate change. We need to protect our special places and the plants and animals that call them home.” The damaging mass bleaching event — the seventh since 1998 — was confirmed by government scientists following aerial surveys of 300 shallow reefs.

The Australian Reef Authority said it would now need to conduct further surveys to assess the severity and extent of bleaching. Coral bleaching occurs when underwater temperatures are more than one degree warmer than the long-term average.

As corals come under heat stress, they expel algae living within their tissues — draining them of their vibrant colours. “Ocean temperatures along the Great Barrier Reef have approached record levels in the past few weeks,” according to official monitoring.

Richard Leck, head of oceans at World Wildlife Fund Australia, said it was likely that masses of coral would die if ocean temperatures did not cool rapidly in the coming weeks. “This bleaching event is unfolding in an area where corals have not been previously exposed to these extreme temperatures,” he said.

Mr. Leck said climate change was “putting tremendous pressure” on the Great Barrier Reef. “The current bleaching event followed similar setbacks in the Northern Hemisphere last year,” Mr. Leck added, which caused major coral mortality in Florida and the Caribbean.

Some species of bleached coral have proven remarkably resilient and can recover if ocean temperatures cool. But professor Terry Hughes, one of Australia’s foremost coral reef scientists, said bleaching events were now happening so frequently that reefs were struggling to recover.

Recovery in danger

“The reef is no longer capable of recovering to the mix of coral species and the sizes of corals that were there 20 years ago,” he told AFP.

“The irony is that the corals that are now prevalent on most parts of the Great Barrier Reef are fast growing and rapidly regain cover, but the kicker is that they are heat sensitive and are less tolerant to the next inevitable beaching event.”

Mr. Hughes said the heat stress had increased in the past few days and would likely worsen in the coming two weeks. The fate of the reef has been a recurrent source of tension between the Australian government and the United Nations’ World Heritage Committee.

The World Heritage Committee has threatened to put the reef on a list of “in danger” global heritage sites, a move that would likely damage its allure for international tourists. Behind-the-scenes diplomacy and fierce lobbying from Australia has so far kept it off the list.

Before this event, Australia’s Great Barrier Reef suffered mass coral bleaching in 1998, 2002, 2016, 2017, 2020 and 2022.