Almost all of Great Barrier Reef coral in Australia is bleached

More than 90 percent of the coral was found recently to be bleached, which is a response to heat.

Coral of the Australia's Great Barrier Reef was recently found to be more than 90 percent bleached, as this coral was in 2015. The bleaching is a stress reaction to heat. December, the first month of summer in the Southern Hemisphere, was the warmest December at the reef since 1900. (C. Jones/AP)

More than 90 percent of Great Barrier Reef coral surveyed this year was 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. This is the reef’s first bleaching event during a La Niña weather pattern, which is associated with cooler Pacific Ocean temperatures, the Great Barrier Reef Marine Authority said in its annual report released Tuesday. The report found that 91 percent of the areas surveyed were affected.

Bleaching in 2016, 2017 and 2020 damaged two-thirds of the coral in the reef off Australia’s eastern coast.

Coral bleaches as a heat-stress response, and scientists hope most of the coral will recover from the current event, said David Wachenfeld, chief scientist at the authority, which manages the reef ecosystem.

“We are hoping that we will see most of the coral that is bleached recover and we will end up with an event rather more like 2020 when, yes, there was mass bleaching, but there was low mortality,” Wachenfeld added.

The bleaching events in 2016 and 2017 led to a large number of coral dying, Wachenfeld said.

Bleaching continues to affect coral reefs

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More than 90 percent of the Great Barrier Reef corals in Australia are bleached, according to Australian government scientists. In this photo supplied by the Great Barrier Reef Marine Park Authority, a diver swims past coral on the Great Barrier Reef in 2016. Coral are known as the rainforest of the sea because of their incredible biodiversity. Moreover, about one-quarter of the ocean’s fish depend on healthy coral reefs. (M. Curnock/Associated Press)

Simon Bradshaw, a researcher at the Climate Council, an Australia-based group that tracks climate change, said the report demonstrated the reef’s survival depended on steep global emission cuts within the decade.

“This is heartbreaking. This is deeply troubling,” Bradshaw said. “It shows that our Barrier Reef really is in very serious trouble indeed.”

December, the first month of the Southern Hemisphere summer, was the hottest December the reef had experienced since 1900. A “marine heat wave” had set in by late February, the report said.

The Great Barrier Reef accounts for around 10 percent of the world’s coral reef ecosystems and was named because of the extensive hazards it posed to 18th-century sailors. The network of more than 2,500 reefs covers 134,000 square miles.

Coral is made up of tiny animals called polyps that are fed by microscopic algae that live inside the reefs and are sensitive to changes in water temperatures.

The algae provide the reefs their kaleidoscope of colors and produce sugars through photosynthesis that provide the coral with most of its nutrients.

Rising ocean temperatures turn the chemicals that the algae produce into toxins. The coral turns white as it effectively spits the poisonous algae out. Heat stress beyond a few weeks can lead the coral to die of starvation.