Most of world's colourful corals go white in record-breaking bleaching

Yahoo

23-04-2025

The world's rainbow reefs have gone ghostly white in seas around the globe.
The "most intense global coral bleaching event ever" has so far struck 84 per cent of the world's reefs and is ongoing, the International Coral Reef Initiative (ICRI) — a global partnership between nations and non-governmental and international organizations focused on sustainable management of coral reefs — reported on Wednesday.
The new figure is far worse than previous events that hit 21 to 68 per cent of reefs.
But scientists say the reefs and the corals are not all dead yet and could still bounce back if people take the right steps, including conservation and cutting greenhouse gas emissions.
Corals are small marine animals that live in colonies with colourful symbiotic algae that give them their rainbow hues and supply them with most of their food. But when the water gets too warm for too long, the algae release toxic compounds, and the corals expel them, leaving behind a white skeleton — causing "bleaching."
The current global bleaching event, the fourth since 1998, started in January 2023, hitting different parts of the world at different times over the past two years, amid record-breaking ocean temperatures.
It was officially declared a global coral bleaching event in April 2024. Last year, the Earth's hottest on record, the oceans also broke a record, hitting an average annual sea surface temperature of 20.87 C away from the poles.
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No end in sight?
The fact that it's ongoing two years later takes the world's reefs "into uncharted waters," Britta Schaffelke, a researcher with the Australian Institute of Marine Science and co-ordinator of the Global Coral Reef Monitoring Network, said in a statement accompanying ICRI's news release.
"In the past, many coral reefs around the world were able to recover from severe events like bleaching or storms," she said.
But the length of this bleaching event and the fact that it is getting longer by the day worries coral scientists.
Mark Eakin, corresponding secretary of the International Coral Reef Society and retired chief of the Coral Reef Watch program of the U.S. National Oceanic and Atmospheric Administration, said it's an open question when — and even if — the current bleaching will end.
"We may never see the heat stress that causes bleaching dropping below the threshold that triggers a global event," he told The Associated Press.
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Valeria Pizarro, a researcher with the non-profit Perry Institute for Marine Science who studies corals in the Caribbean, said bleaching used to sometimes happen at the end of summer, when the waters are at their warmest.
But the current event started in her region in July, and temperatures are already 30 C to 32 C, when they're usually 28 C at this time of year.
It has also damaged even very common species, she said, adding, "That is shocking."
Nicola Smith, an assistant professor of biology at Montreal's Concordia University who also studies coral reefs in the Caribbean, noted that the Intergovernmental Panel on Climate Change has projected that coral reefs will decline 70 to 90 per cent if the global temperature warms to 1.5 C above pre-industrial temperatures.
"We're seeing it play out before our eyes," she said. "This is what it's going to look like, not just in summer during bleaching, but year-round."
Smith said the loss of coral reefs could harm many fish and other marine creatures.
A report from the Intergovernmental Panel on Climate Change projected that if the world warms 1.5 C, there will be a 70 to 90 per cent decline in coral reefs. (CBC)
"They provide literally thousands of other species with habitat as well as food, as well as shelter and sites for reproduction."
The ICRI said not only does a third of marine life rely on coral reefs, but also a billion people — both directly and indirectly — for things like food, tourism and protection from storms. It estimates they contribute $10 trillion to the global economy.
Not dead yet
Still, the ICRI thinks corals can still survive this century if people take conservation measures and cut greenhouse gas emissions to slow ocean warming. And other scientists say despite the grim news, corals can often withstand and bounce back from bleaching.
Melanie McField, founder and director of the Florida-based non-profit Healthy Reefs for Healthy People, said even without their food-supplying symbiotic algae, corals starve to death very slowly.
"It ... takes months usually," she said. "They're kind of hanging on. Part of it is alive, it's partly dead."
And even if the coral dies, other reef organisms such as sponges and crusty, pink coralline algae live on.
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"The Australians call it living dead. So you've still got a reef, you've still got some fish around," McField said. "Everything is kind of brown and grey."
But the reef is vulnerable at that point, as sponges, worms and other creatures eat into the coral that is no longer rebuilding itself.
"And then when that hurricane comes, it turns into rubble," McField said.
She said that can be scary for people living on coasts protected by the coral reefs: "It's life and security."
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The ICRI estimates that to save coral reefs and the people who rely on them, spending on solutions needs to increase sevenfold. Things that could help include selective breeding, coral restoration, reducing pollution and stopping overfishing.
McField said that so far, a lot of those strategies are "very small little efforts at this time" and more of them are needed.
Tiny fish hover over bleached corals in Ningaloo, Western Australia, in a February 2025 photo. Sponges and other marine creatures may still remain, and the corals may not be dead yet. (Daniel Nicholson/Ocean Image Bank)
But keeping the global temperature as little above 1.5 C as possible is "necessary to give these coral conservation measures a chance to work," the ICRI said.
McField agrees. "You can have all these efforts at 1.5 or 1.6 or 1.7, but probably not 2.... Don't go above that [or] I'm not sure we're going to be able to save them."