The World’s Coral Reefs Are Bleaching. What Does That Mean?

This July 26, 2023 image provided by phade® by WinCup, Inc., shows a "Coral Fort," made of biodegradable drinking straws that researchers are using to prevent laboratory-grown coral from becoming really expensive fish food, off the coast of Fort Lauderdale, Fla. (Chris Gug/phade® by WinCup, Inc. via AP)
This July 26, 2023 image provided by phade® by WinCup, Inc., shows a "Coral Fort," made of biodegradable drinking straws that researchers are using to prevent laboratory-grown coral from becoming really expensive fish food, off the coast of Fort Lauderdale, Fla. (Chris Gug/phade® by WinCup, Inc. via AP)
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The World’s Coral Reefs Are Bleaching. What Does That Mean?

This July 26, 2023 image provided by phade® by WinCup, Inc., shows a "Coral Fort," made of biodegradable drinking straws that researchers are using to prevent laboratory-grown coral from becoming really expensive fish food, off the coast of Fort Lauderdale, Fla. (Chris Gug/phade® by WinCup, Inc. via AP)
This July 26, 2023 image provided by phade® by WinCup, Inc., shows a "Coral Fort," made of biodegradable drinking straws that researchers are using to prevent laboratory-grown coral from becoming really expensive fish food, off the coast of Fort Lauderdale, Fla. (Chris Gug/phade® by WinCup, Inc. via AP)

Huge stretches of coral reef around the world are turning a ghostly white this year amid record warm ocean temperatures.

On Monday, the US National Oceanic and Atmospheric Administration confirmed the world's fourth mass global bleaching event is underway - with serious consequences for marine life and for the people and economies that rely on reefs.

Here's how warming affects coral reefs and what the future might hold for these fragile underwater ecosystems.

WHAT ARE CORALS?

Corals are invertebrates that live in colonies. Their calcium carbonate secretions form hard and protective scaffolding that serves as a home to many colorful species of single-celled algae.

The two organisms have evolved over millennia to work together, with corals providing shelter to algae, while the algae remove coral waste compounds and deliver energy and oxygen back to their hosts.

WHY DO CORALS MATTER?

Coral reefs cover less than one percent of the ocean floor, but have out-sized benefits for marine ecosystems and economies.

A quarter of marine life will depend on reefs for shelter, finding food or spawning at some point in their lives and coastal fisheries would struggle without corals.

Every year, reefs provide about $2.7 trillion in goods and services, from tourism to coastal protection, according to a 2020 estimate by the Global Coral Reef Monitoring Network. About $36 billion is generated by snorkeling and scuba diving tourists alone.

Coral reefs also help coastal communities by forming a protective barrier against storm surges and large waves. This helps to avoid property damage for more than 5 million people worldwide, a 2022 study in the journal Marine Policy found.

WHAT IS CORAL BLEACHING?

When water temperatures rise, jewel-toned corals get stressed. They cope by expelling their algae — causing them to turn bone white.

Most corals live in shallow waters, where climate-driven warming is most pronounced.

Whether a coral becomes heat-stressed depends on how long the high temperatures last, and how much warmer they are than usual.

Scientists have found that corals generally begin to bleach when surrounding waters are at least 1 degree Celsius warmer than the maximum average temperature - or the peak of what corals are used to - and persist for four or more weeks.

WHAT IS GOING ON WITH OCEAN TEMPERATURES THIS YEAR?

This year has seen an explosive and sustained bout of ocean heat as the planet deals with the effects of both climate change and an El Nino climate pattern, which yields warmer seas.

In March, global average sea surface temperature (SST) reached a record monthly high of 21.07C (69.93F), according to the EU Copernicus Climate Change Service.

"There's been a pretty large step change in the global average SST this year," said Neal Cantin, a coral biologist with the Australian Institute of Marine Sciences. "We're certainly in a new regime. Corals clearly aren't keeping up".

As the El Nino weakens, scientists say some of that ocean heat should diminish. But overall ocean warming will continue as climate change intensifies.

DO ALL BLEACHED CORALS DIE?

Corals can survive a bleaching event if the surrounding waters cool and algae return.

Scientists at the Palau International Coral Reef Center estimate that it takes at least nine to 12 years for coral reefs to fully recover from mass bleaching events, according to research published in 2019.

Disruptions such as cyclones or pollution can slow the recovery.

"Bleaching is like a fever in humans," said ecologist David Obura, director of Coastal Oceans Research and Development in the Indian Ocean East Africa. "We get a fever to resist a disease, and if the disease is not too much, we recover. But if it is too much, we die as a result."

Scientists caution that corals this year have faced harsher and more prolonged high temperatures than ever before.

"What is happening is new for us, and to science," said Lorenzo Alvarez-Filip, a coral reef ecologist at the National Autonomous University of Mexico. "We cannot yet predict how severely stressed corals will do even when they survive the stress event, or how coral recovery will operate."

WHAT HAPPENS TO DEAD CORALS?

Dead reefs can still offer shelter to fish or provide a storm barrier over several years for coastal communities.

But eventually, these underwater graveyards of calcium carbonate skeletons will erode and break apart.

"It might take 10, even 20 years to see these consequences," Alvarez-Filip said.

WHAT CAN BE DONE TO HELP SAVE REEFS?

The best chance for coral survival is for the world to cut greenhouse gas emissions to limit climate change.

Many scientists think that at just 1.2C of warming above preindustrial level, the world has already passed a key threshold for coral reef survival. They expect between 70% and 90% of the world's coral reefs will be lost.

Scientists and conservationists are scrambling to intervene.

Local communities have cleanup programs to remove litter from the reefs to reduce further stresses. And scientists are breeding corals in labs with the hopes of restoring degraded reefs.

However, none of this is likely to work to protect today's corals from warming waters. Scientists are therefore trying to plan for the future by bringing coral larvae into cryopreservation banks, and breeding corals with more resilient traits.

Obura said that while it's important that scientists investigate such interventions, breeding genetically engineered corals is not the answer to climate change. "We have to be very careful about stating that it's the solution and that it's saving corals reefs now," he said.

"Until we reduce carbon emissions, they won't save coral reefs."



Year after Exodus, Silence Fills Panama Island Threatened by Sea

The evacuation of around 1,200 members of the Indigenous Guna community to a new life on the mainland was one of the first planned migrations in Latin America due to climate change. MARTIN BERNETTI / AFP
The evacuation of around 1,200 members of the Indigenous Guna community to a new life on the mainland was one of the first planned migrations in Latin America due to climate change. MARTIN BERNETTI / AFP
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Year after Exodus, Silence Fills Panama Island Threatened by Sea

The evacuation of around 1,200 members of the Indigenous Guna community to a new life on the mainland was one of the first planned migrations in Latin America due to climate change. MARTIN BERNETTI / AFP
The evacuation of around 1,200 members of the Indigenous Guna community to a new life on the mainland was one of the first planned migrations in Latin America due to climate change. MARTIN BERNETTI / AFP

Streets once filled with children's laughter have fallen silent on a Panamanian island where almost all residents left a year ago due to the threat of the sea swallowing their homes.

The evacuation of around 1,200 members of the Indigenous Guna community to a new life on the mainland was one of the first planned migrations in Latin America due to climate change.

The exodus from Gardi Sugdub in the Caribbean left those who remained with a sense of sadness, said Delfino Davies, who has a small museum on the island with spears, jars and animal bones.

"There are no friends left or children playing," he told AFP.

Gardi Sugdub now has the silence of a "dead island," he said.

Dusty desks and empty classrooms are all that remain of a school that once bustled with children.

Many of the island's wooden houses are padlocked.

"There's no one here. Sometimes I get sad when I'm here alone," Mayka Tejada, 47, said in the small store where she sells bananas, pumpkins, clothes, toys and notebooks.

Like Davies and about 100 others, she decided to stay.

But her mother and two children, aged 16 and 22, moved to one of the 300 houses built by the Panamanian government in a new neighborhood called Isber Yala on the mainland, a 15-minute boat ride away.

Gardi Sugdub, the size of around five football fields, is one of 49 inhabited islands in the Guna Yala archipelago -- also known as San Blas -- which scientists warn is in danger of disappearing by the end of the century.

'I'll die here'

Sitting in a hammock in her earthen-floor house filled with the aroma of medicinal herbs, 62-year-old Luciana Perez said she had no intention of leaving.

"I was born in Gardi and I'll die here. Nothing is sinking. Scientists don't know, only God," she said.

Perez said that she was not afraid because since she was a child she had seen big waves and rising waters flooding houses at times.

Steven Paton, a scientist at the Panama-based Smithsonian Tropical Research Institute, said climate change meant that sea levels were expected to rise by up to 80 centimeters.

"Most of the Guna Yala islands are about 50 centimeters above sea level," he told AFP. "They'll be underwater."

Ana Toni, CEO of the United Nations' COP30 climate conference, told AFP that the mass evacuation "shows the reality we already have to face on the planet."

Sidewalks, water, electricity

The arrival of the rainy season has left puddles dotting the dirt roads of Gardi Sugdub.

In contrast, in the new settlement of Isber Yala -- "land of loquats" in the Guna language -- the streets are paved and have sidewalks.

The nearly 50-square-meter (500-square-feet) concrete houses have flushing toilets and there is a plot of land to grow vegetables.

On Gardi Sugdub "we lived crowded together, and I had to go fetch water from the river in a small boat," said Magdalena Martinez, a 75-year-old retired teacher.

In Isber Yala, water is available for an hour in the morning, she said.

"I can fill the buckets. And I have electricity 24 hours a day," said Martinez, who lives with her granddaughter in the new neighborhood.

Tejada's children also have no regrets about leaving the island, she said.

"I miss them, but they're happy there. They have a place to play football and walk around," Tejada said.

While the island's school relocated to Isber Yala, its dilapidated clinic remained in Gardi Sugdub.

"Before, people came on foot. Now, they have to travel by land and sea to get here. There are fewer visitors," said 46-year-old doctor John Smith.

Some of the islanders divide their time between the two communities, while others visit occasionally to check on their homes.

This week, there will be more activity than normal: seven jars of chicha -- a fermented corn drink -- are ready for Isber Yala's first anniversary.

Martinez is looking forward to the celebration, even though it will be bittersweet.

Although she may not see it herself, "the islands will disappear because the sea will reclaim its territory," she said.