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The consecutive coral bleaching episodes that damaged two-thirds of the Great Barrier Reef in Australia in 2016 and 2017 have had a lasting impact on the health of the largest living structure on the planet.
A study published in Nature on Wednesday revealed that the death of corals in 2016 and 2017 had significantly reduced the ability of new corals to grow and prosper. In 2018, the number of new corals on the reef decreased by 89% compared to the historical record.
"Dead corals do not make babies," said Terry Hughes, lead author and professor at James Cook University, as reported by BBC News.
Researchers at the ARC Center of Excellence for Coral Reef Studies in Australia were surprised by the magnitude of the decline in new corals. It was the first time that they observed such a decline on the reef.
"We thought the coral reef was too big to go bankrupt," said chief investigator Andrew Baird of The New York Times, "but that's not the case".
Baird added that the study was the first to document the collapse of the processes of an oceanic ecosystem.
Bleaching occurs when hot water forces the corals to expel the algae that give them color and nutrients. Reefs can recover from such events, but it takes about a decade. The Great Barrier Reef has experienced four since 1998 and, if greenhouse gas emissions are maintained at current levels, there could be two bleaching episodes per decade starting in 2035.
The number of more recent bleaching events – covering 900 miles of reefs – has also made it harder to rebuild baby coral populations, BBC News said.
"Babies can travel long distances and if a reef is knocked out, there are usually plenty of adults in another reef to provide juveniles," Baird told BBC News. "Now, the magnitude of the mortality is such that there is nothing left to replenish the reef."
Bleaching has affected some corals more than others. The new corals of Acropora have decreased by 93%. Table-shaped corals are responsible for the three-dimensional structure of the reef and provide habitat for species such as coral trout and clownfish.
"We have always anticipated that climate change would alter the composition of coral," Hughes told National Geographic. "What surprised us is the speed with which it happens, it does not happen in the future, it's something we measure now."
A study conducted in 2018 had hoped that the corals surviving the bleaching of 2016 would also be better able to withstand the event of 2017. Researchers are trying to replicate the most resistant corals, but the Coral Reef Watch coordinator, from the National Oceanic and Atmospheric Administration, said, who did not participate in the study, told The New York Times that such projects could not replenish the entire reef.
"These are at the scale of a large family garden," he said, as the threat to the Great Barrier Reef could result in "the loss of a whole seascape." ".
Baird seemed to agree.
"We are now at the point where local solutions for the reef are almost useless – the only thing that matters is the action on climate change," Baird told BBC News.
Coral bleaching at Heron Island, on the Great Barrier Reef, in January 2016.
The Ocean Agency / XL Catlin Seaview Survey / Richard Vevers
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