Huge stretches of coral reef around the world are turning a ghostly white this year amid record warm ocean temperatures.
Coral reefs around the world are experiencing global bleaching for the fourth time, top reef scientists declared Monday, a result of warming ocean waters amid human-caused climate change.
On Monday, the U.S. 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.
Coral reef bleaching across at least 53 countries, territories or local economies has been confirmed from February 2023 to now, scientists from the National Oceanic and Atmospheric Administration and International Coral Reef Initiative said. It happens when stressed coral expel the algae that are their food source and give them their color. If the bleaching is severe and long-lasting, the coral can die.
Coral reefs are important ecosystems that sustain underwater life, protect biodiversity and slow erosion. They also support local economies through tourism.
Bleaching has been happening in various regions for some time. In the world’s largest coral reef ecosystem, Australia’s Great Barrier Reef, bleaching affected 90% of the coral assessed in 2022. The Florida Coral Reef, the third-largest, experienced significant bleaching last year.
But in order for bleaching to be declared on a global scale, significant bleaching had to be documented within each of the major ocean basins, including the Atlantic, Pacific, and Indian oceans, in both the Northern and Southern Hemispheres.
Monday’s news marks the second worldwide bleaching event in the last 10 years. The last one ended in May 2017. Brought on by a powerful El Nino climate pattern that heated the world’s oceans, it lasted three years and was determined to be worse than the prior two bleaching events in 2010 and 1998.
This year’s bleaching follows the declaration that 2023 was the hottest year on record.
“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Derek Manzello, NOAA Coral Reef Watch coordinator, said in a statement.
Selina Stead, a marine biologist and chief executive of the Australian Institute of Marine Science, called climate change “the biggest threat to coral reefs worldwide.” She said scientists are working to learn more about how coral responds to heat and to identify naturally heat-tolerant corals, but said it is “critical the world works to reduce carbon emissions.”
One reef that fared better than others last year was the Flower Garden Banks National Marine Sanctuary, which was afforded some protection by its location in deeper water in the Gulf of Mexico about 100 miles off the Texas coast. Sanctuary officials didn’t immediately respond to messages Monday seeking the latest on the health of the sanctuary’s corals.
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 colourful 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 snorkelling 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, opens new tab 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.
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 programmes 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.” (AP/Reuters)
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