Record-breaking warm waters have bleached large parts of Australia's Great Barrier Reef this year, as they did in 2016 and 2017, scientists reported Thursday, the latest sign that global warming threatens the health of one of the ecosystems. most important marine in the world.
"We can confirm that the Great Barrier Reef is experiencing its third massive bleaching event in five years," David Wachenfeld, chief scientist for the Great Barrier Reef Marine Park Authority, said in a video posted on his website.
Water that is warmer than normal stresses corals that create a reef, causing them to lose color and even turn white. Corals that experience mild or moderate bleaching generally recover, but those that severely bleach often die.
Scientists say reefs around the world have been dying at an alarming rate for several years due to global warming. Coral reefs grow very slowly, and although most of them can only live in warm waters, they are very sensitive to above-normal temperatures.
The Great Barrier Reef is estimated to be compatible with thousands of marine species, and is essential to the lives of some Aboriginal groups and the natives of the Torres Strait Islands, between the Australian continent and New Guinea.
It also promotes important economic activities such as tourism and fishing; Scientists said important reef tourism areas, particularly in the north, have not been seriously affected this year.
The Great Barrier Reef Authority, an Australian government agency, based its massive bleaching announcement on observations, still ongoing, made in the water and from the air.
The data is new. But the same weather patterns that generated Record heat and catastrophic fires in Australia during the southern hemisphere spring and summer have also warmed the oceans.
In terms of water temperatures around the reef, February was the warmest month on record, with readings in places more than 5 degrees Fahrenheit above average for the time of year, the authority recently reported.
"The Great Barrier Reef remains under pressure from the heat stress that built up during the 2019/20 summer, particularly in February and early March 2020, and the resulting bleaching that is occurring," the authority said in a statement released Thursday.
The reef, truly a network of hundreds of reefs, is the largest in the world, with more than 1,100 miles in the Pacific Ocean, off the tropical coast of Northeast Australia. It is primarily made up of the bleached remains of countless past generations of corals and mollusks, with live corals and other invertebrates clinging to its surface.
"Some reefs that have been surveyed have had no bleaching, even on reefs with very severe bleaching, with 80 percent or more of the observed corals being bleached," said Dr. Wachenfeld.
Considering 2016 and 2017, he added, "many of those reefs are blanching for the third time."
In 2017, after the last massive bleaching, scientists reported that large stretches of the reef were dead or dying.
Last year, before the recent heat wave and bleaching, the authority released a detailed assessment of the reef's prospects, an analysis that is done every five years. Of the dozens of ecological indicators he measured, about 40 percent "are in poor condition," he said, and "some critical ecosystem functions have deteriorated since 2014."
The governments The Reef 2050 plan aims to reduce water pollution that also threatens corals, regulating factors such as agricultural runoff, dredging, and port development. There are also programs to control sudden spikes in the population of crown-crowned starfish, which feed on coral.
But those measures cannot compensate for the damage caused by global warming, scientists warn.
"Climate change," the reef authority said Thursday, "remains the biggest challenge for the reef."