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This year, record warm ocean temperatures have turned vast coral reefs around the world ghostly white.
On Monday, the National Oceanic and Atmospheric Administration confirmed that the world’s fourth major global bleaching event is underway, severely impacting the people and economies that depend on marine life and coral reefs.
Here’s how global warming is impacting coral reefs and what the future holds for this fragile underwater ecosystem.
What is coral?
Corals are invertebrates that live in colonies. Calcium carbonate secretions form a hard, protective scaffold that serves as a home for many colorful unicellular algae.
These two organisms have evolved together over thousands of years, with the coral providing shelter for the algae, and the algae removing waste compounds from the coral and sending energy and oxygen back to the host. Ta.
Why are corals important?
Although coral reefs occupy less than 1% of the ocean floor, they provide immense benefits to marine ecosystems and economies.
A quarter of all marine life will depend on coral reefs at some point in their lives to find shelter, food, or spawn, and coastal fisheries would be difficult without them.
Coral reefs provide approximately $2.7 trillion in goods and services each year, from tourism to coastal protection, according to 2020 estimates from the Global Coral Reef Monitoring Network. Approximately $36 billion is generated from snorkeling and scuba diving tourists alone.
Coral reefs also help coastal communities by forming a protective barrier against storm surges and large waves. This could help more than 5 million people around the world avoid property damage, his 2022 study published in the journal Ocean Policy found.
What is coral bleaching?
As water temperatures rise, jewel-colored corals become stressed. They deal with it by expelling the algae and turning it white.
Most corals live in shallow waters where climate-induced warming is most pronounced.
Whether corals experience heat stress depends on how long the high temperatures last and how much warmer the corals are than normal.
Scientists have found that coral bleaching typically begins when the surrounding body of water is at least 1 degree Celsius warmer than the highest average water temperature, the peak temperature to which corals are accustomed, and bleaching continues for four weeks or more.
What is the sea temperature like this year?
This year has seen explosive and sustained ocean heating as the planet grapples with the effects of both climate change and El Niño, which causes ocean temperatures to rise.
Global mean sea surface temperatures (SST) in March reached a monthly record of 21.07 degrees Celsius (69.93 degrees Celsius), according to the EU Copernicus Climate Change Agency.
“There has been quite a significant change in global average sea surface temperatures this year,” said Neil Cantin, a coral biologist at the Australian Institute of Marine Science. “We are certainly in a new regime. Corals are clearly not catching up.”
As El Niño weakens, some of the ocean heat should decrease, scientists say. But as climate change intensifies, ocean-wide warming will continue.
Do all bleached corals die?
Corals can survive bleaching events when the surrounding seawater cools and the algae return.
According to research published in 2019, scientists at the Palau International Coral Reef Center estimate that it will take at least nine to 12 years for coral reefs to fully recover from a large-scale bleaching event.
Disruptions such as cyclones and pollution can delay recovery.
“Bleaching is like a fever for humans,” says ecologist David Obra, director of coastal marine research and development in the Indian Ocean East Africa. “We develop a fever to fight the disease, but if the disease is not severe we recover. But if it is too much, we die as a result.”
Scientists have warned that this year corals are being exposed to harsher and longer-term high temperatures than ever before.
“What’s happening is new for us and for science,” said Lorenzo Álvarez Philippe, a coral reef ecologist at the National Autonomous University of Mexico. “We still cannot predict how severely stressed corals will be affected even if they survive the stress event, or how coral recovery will work.”
What happens to dead coral?
Dead coral reefs can still provide refuge for fish or provide seawalls for coastal communities for years.
But eventually, these underwater graveyards of calcium carbonate skeletons erode and fall apart. “It may take 10 or even 20 years to see these results,” Alvarez-Philippe said.
What can be done to save coral reefs?
Corals’ best chance of survival is if the world reduces greenhouse gas emissions to limit climate change.
Many scientists believe that with just 1.2 degrees of warming above pre-industrial levels, the world has already surpassed a threshold critical to the survival of coral reefs. They predict that 70% to 90% of the world’s coral reefs will be lost.
Scientists and conservationists are desperate to intervene.
Local communities are implementing clean-up programs to remove debris from coral reefs to reduce further stress. And scientists are breeding corals in the lab in hopes of restoring degraded reefs.
However, none of these appear to be helpful in protecting current corals from rising ocean temperatures. So scientists are planning for the future by bringing coral larvae to cryopreservation banks and breeding corals with more resilient traits.
Obra said it was important for scientists to investigate such interventions, but breeding genetically modified corals was not a solution to climate change. “We need to be very careful about claiming that this is the solution and that we are now saving the reef,” he said.
“Coral reefs will not be saved unless we reduce carbon emissions.”
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