Study: The Great Barrier Reef loses its ability to recover after bleaching


The 2,300 km (1,500 mile) long reef has undergone numerous large "bleaching" caused by above-average water temperatures over the past two decades, including consecutive events in 2016 to 2017.
The new study, published Wednesday in the journal Nature, examined the number of adult corals that survived both events and the number of new corals created to rebuild the reef in 2018.

The answer was as bleak as it was striking: "Dead corals do not make babies," said lead author Terry Hughes in a press release.

Scientists in the study found that the loss of adult coral caused a "coral re-creation crash" on the reef, as thermal stresses from warming ocean temperatures affected coral healing capacity .

"The number of new corals that have settled on the Great Barrier Reef has declined 89% as a result of the unprecedented loss of adult coral due to global warming in 2016 and 2017," said Hughes.

Scientists have long warned of the impact of global warming on the reef, the world's largest reef system and the only living organism visible from space. The reef, a UNESCO World Heritage Site, is home to thousands of species – fish, turtles, sharks and marine mammals.

In the introduction to the report, the authors note that the environmental changes caused by climate change "are increasingly testing the ability of ecosystems to absorb recurrent shocks and to reassemble afterwards, which increases the risk of widespread ecological collapse of the current ecosystem ".

The study revealed that one of the most dominant coral species, Acropora, which provides "most of the three-dimensional coral habitat that hosts thousands of other species", according to co-author Andrew Baird, experienced a 93% drop in its replenishment. following the consecutive whitening episodes of 2016 and 2017.

Dark future

Scientists working on this report expect coral recruitment to recover over the next 5 to 10 years as more corals reach sexual maturity, but only in the absence of another event. whitening. However, with the continuing rise in sea temperatures, this seems to be an impossibility.

"It is highly unlikely that we can escape a fifth or sixth event of the next decade," said co-author Morgan Pratchett.

"We used to think that the Great Barrier Reef was too big to go bankrupt – until now," he said.

Recent bleaching follows two previous events in 1998 and 2002. Scientists predict that gaps between bleaching events will only decrease as climate change worsens.

"The resilience of the reefs is now severely compromised by global warming," said Baird.

Previously, when part of the reef had been damaged, for example by a cyclone, other parts would seed the affected area with coral larvae, said another co-author, Morgan Pratchett.

"But now, the magnitude of the damage caused by the extreme heat in 2016 and 2017 was nearly 1500 km (932 miles), a distance well above that of a cyclone."

He stated that, although the areas of the reef to the south that are still in good condition due to colder waters escaping bleaching, they are too geographically distant to seed the affected areas farther north.

"There is only one way to solve this problem," says Mr. Hughes, "and that is to tackle the root cause of global warming by reducing net zero greenhouse gas emissions as quickly as possible ".

Start of an "ecological collapse"

John Veron, a renowned reef expert widely known as the "godfather of coral", told CNN in 2018 that a quarter or a third of all marine species crossing the ocean were living part of their cycle of life in coral reefs.

"So, you're removing the coral reefs and a third to a quarter of all marine species are being wiped out." Now, it's ecological chaos, it's ecological collapse … C & # 39; is the beginning of a global disaster, "said Veron.

The mass-laundering events of recent years – and the prospect of losing one of nature's greatest treasures – should be seen as a warning to the world as part of the broader battle against climate change said Veron.

"It's more than an alarm bell," Veron said. "It's an air raid siren."

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