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Following a major long-term study, scientists have revealed that Australia's Great Barrier Reef suffered a “catastrophic death” of coral during a prolonged heat wave in 2016, threatening a wider range of reef life than previously feared. previously.
The underwater heat wave that bleached massive sections of the reef in 2016 was so severe that it immediately “cooked” some coral in the northern region.
The French news agency AFP reports that 30% of the reef's coral died in the heat wave between March and November 2016, the first of two consecutive years of unprecedented coral bleaching along the 2,300-kilometer reef of the World Heritage in northern Australia -the east coast.
The study, published today in the journal Nature, found that corals, which serve as habitats for other creatures, were particularly affected by rising sea temperatures caused by global warming.
Professor Terry Hughes, co-author of the report and head of the Center of Excellence for Coral Reef Studies at Australia's James Cook University, told AFP that the most vulnerable to heat exposure are branched corals, table-shaped creatures. They provide nooks and crannies for fish and fisheries nurseries.
The corals that were most likely to survive warmer sea temperatures were soft and melon-shaped, he said.
"While they were good calcifiers that increase the volume of reefs, they were not" very useful as habitable providers. "
"So there is a change in the mix of species and the overall loss of corals has a broader impact on all creatures that depend on corals for food and habitats," said Professor Hughes.
The findings come as a United Nations scientific advisory body considers which parts of the natural world are on the brink of environmental failure.
The JCU researchers said their work showed that climate change threatened the Great Barrier Reef with ecological collapse.
The research center said the new study showed that corals in the northern Great Barrier Reef "experienced a catastrophic death" after the 2016 heat wave.
"The extinction of corals has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are transforming into more degraded systems, with only a few hard species remaining," said the Professor Andrew Baird, another of the report's authors.
The scientists said the focus should be on protecting the surviving corals, which number about 1 billion after the two bleaching events in 2016 and 2017.
"They are the ones who are going to re-feed and repopulate an altered reef in the future," said Professor Hughes, adding that one way to maintain their health was to improve water quality by reducing coastal pollution.
They concluded that the 2016 bleaching event was the beginning of a long-term transformation, which has altered the Great Barrier Reef "forever."
Efforts to curb climate change, such as the United Nations-sponsored Paris Agreement to limit global warming to less than 2.0 degrees Celsius below pre-industrial levels, were also critical.
"We have now seen four fading events (1998, 2002, 2016 and 2017) in the Great Barrier Reef with one degree (Celsius) of average global warming," he said.
“We are on a path where we are committed to a different barrier reef. If we continue with the usual emissions, then I don't think the reef can survive. "
Coral reefs represent less than one percent of the Earth's marine environment, but are home to about 25 percent of marine life, acting as nurseries for many species of fish.
The Australian government's Great Barrier Reef Marine Park Authority concluded that the bleaching in 2016 was caused by a record marine heat wave, caused by a combination of climate change and the El Niño climate cycle.
Dr. Sarah Perkins-Kirkpatrick from the University of New South Wales Center for Climate Change Research recently published work showing that underwater heat waves have increased in duration and frequency over the past century, with a sudden rebound since the 1980s.
As a result, on average around the world, there are 54 percent more days each year that are subject to a marine heat wave.
"The type of events that cause coral bleaching will occur more frequently in the future," said Dr. Perkins-Kirkpatrick.
She added that she was shocked by the results of Professor Hughes' paper.
“I have to say that it is catastrophic. Looking at all the news articles and watching them evolve, it seemed catastrophic, "he said.
By David Twomey
Original article (in English)