More than 90 percent of the Great Barrier Reef corals surveyed this year were bleached in the fourth such mass event in seven years in the world’s largest coral reef ecosystem, Australian government scientists said.
Bleaching is caused by global warming, but it is the first reef bleaching during La Niña time, linked to lower temperatures in the Pacific, the Great Barrier Reef Maritime Administration said in an annual report released late Tuesday. , which found 91 percent of the surveyed areas were affected.
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Bleaching in 2016, 2017 and 2020 damaged two-thirds of the coral in the famous reef off the east coast of Australia.
Corals are bleaching in response to heat stress, and scientists hope most of the corals will recover from the current event, said David Wachenfeld, chief scientist at the body that manages the reef ecosystem.
“The first indications are that mortality will not be very high,” Wachenfeld said on Wednesday.
“We hope to see that most of the bleached corals are recovering and we will end with an event, more like 2020, when, yes, there was mass bleaching, but there was low mortality,” added Wachenfeld.
Bleaching is worse in some years than in others than in others
The whitening events of 2016 and 2017 led to “fairly high coral mortality rates,” Wachenfeld said.
Simon Bradshaw, a researcher at the Climate Council, an Australian-based group that monitors climate change, said the report shows that the reef’s survival depends on a sharp reduction in global emissions over the decade.
“It’s heartbreaking. That’s deeply disturbing, “Bradshaw said. “This shows that our Barrier Reef is really in very serious trouble.”
These aerial photos show the Great Barrier Reef in Australia on December 2, 2017. The Great Barrier Reef represents about 10 percent of the world’s coral reef ecosystems (Kyodo News / The Associated Press)
Last December, the first month of summer in the Southern Hemisphere, was the hottest December the reef had experienced since 1900. A “sea wave” surfaced in late February, the report said.
A United Nations delegation visited the reef in March to assess whether the World Heritage reef list should be downgraded due to the devastation of climate change.
In July last year, Australia garnered enough international support to delay UNESCO, the UN’s cultural organization, from lowering the reef’s World Heritage status to “endangered” due to climate change damage.
But the issue will be back on the agenda of the World Heritage Committee at its annual meeting next month.
The Great Barrier Reef accounts for about 10% of the world’s coral reef ecosystems and is named for the great dangers it posed to 18th century sailors. The network of more than 2,500 reefs covers 348,000 square kilometers (134,000 square miles).
Why heat causes bleaching
Coral consists of small animals called polyps that feed on microscopic algae that live inside reefs and are sensitive to changes in water temperatures.
Algae provide reefs with their kaleidoscope of flowers and produce sugars through photosynthesis, which provides corals with most of their nutrients.
Rising ocean temperatures turn algae-producing chemicals into toxins. Coral turns white because it effectively spits out poisonous algae.
Heat stress in a few weeks can cause corals to starve.
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