Great Barrier Reef shows 89% decline in baby coral settlement

For millenniums, ecosystems have withstood fires, floods, heat waves, drought and even disease by adapting and rebuilding their biodiverse communities. But according to new research, there is a limit to what even the largest and most resilient places can stand, and climate change is testing that limit by repeatedly disturbing one of the earth’s most precious habitats: the Great Barrier Reef.

The study, released Wednesday in the journal Nature by researchers from the ARC Centre of Excellence for Coral Reef Studies in Australia, monitored the death and birth of corals following ocean heat waves that caused mass bleaching of the Great Barrier Reef in 2016 and 2017.

Not only did many of the adult corals die off, but for the first time, researchers observed a significant decline in new corals settling on the reef, compromising its capacity to recover. "There are so many corals, and it's been disturbed many times in the past," said Andrew Baird, chief investigator at the research centre and one of the paper's lead authors. "We never thought we'd see this happen," he said. The study is the first to show the collapse of fundamental ecosystem processes in a marine environment, Mr Baird said. "We thought the Barrier Reef was too big to fail," he said, "but it's not." The Great Barrier Reef, off Australia's east coast, covers 344, 468 sq km (133,000 sq miles) and can be seen from outer space. It pumps AU$6.4 billion (€4 billion) into the Australian economy per year and supports tens of thousands of jobs, according to 2017 figures from Deloitte.

But in recent years, research has shown that the time left to save it is growing short. Since 1998, the Great Barrier Reef has suffered four mass bleaching events, two of them back to back in 2016 and 2017. While coral populations can recover from a bleaching event, which stresses individual corals and strips them of their vibrant colour, they need up to a decade to do so. And if carbon emissions continue at the high-emissions scenario, bleaching will occur twice every decade starting in 2035, and annually after 2044, according to climate models from Unesco.

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“It’s not too late to act, but time is running out,” Mr Baird said, adding that without drastic climate action, reefs will be “fundamentally changed, as will everything.” Coral reefs were among the first ecosystems to respond to the rise in global temperatures, he said, “but it’s only a matter of time before these changes are happening in our back gardens.” According to the researchers’ findings, the settlement of baby corals on the reef declined 89 per cent last year. The coral that experienced the most significant decline in new organisms, at 93 per cent, was a type called Acropora, which provides most of the reef habitat that supports thousands of other species, including coral trout, clown fish and triggerfish.

‘No lucky escape’

Adult corals that were further south escaped bleaching, but they were too far from the bleached northern reefs to help them replenish, the scientists found. They also explored the impact of back-to-back cyclones in 2014 and 2015 on the reef’s north at Lizard Island, which, despite killing off 80 per cent of the adult corals, did not cause a decline in new corals settling.

“Cyclones are fairly patchy,” Mr Baird said, whereas heat and bleaching “just kills everything.” The corals that do manage to survive such trauma, however, were found to be more resistant to periods of extreme warmth in a separate study conducted by Mr Baird and his colleagues last year. Scientists have tried to breed the most resilient forms of coral in the hope that they can use these to repopulate the reef.

While crucial, such projects are limited, said Mark Eakin, the co-ordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch program, who was not involved in the study but has previously worked with the Australian researchers.

“Those are at the scale of a large family garden,” he said of the restoration efforts, whereas the collapse of the Great Barrier Reef would mean “the loss of an entire seascape,” akin, he said, to the fall of the Roman Empire. “This is just further evidence of how much damage climate change is having,” Mr Eakin said. Russ Babcock, a senior research scientist at an Australian government agency called the Commonwealth Scientific and Industrial Research Organisation, said the study, which he was also not involved in, had confirmed many scientists’ worst fears.

“All ecosystems have some things in common, and one of them is the ability to recover,” he said. “There’s going to be no lucky escape.” –New York Times