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 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
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.