SYDNEY, Australia – When Terry Hughes surveyed the Great Barrier Reef from a small plane four years ago and mapped the bleaching and death of corals from water warmed by climate change, he hoped that such a rare and heartbreaking scene would not recur so quickly would.
But rising temperatures sent him back in the air in 2017 when the reef was bleached again. Then he returned last month, which led to another devastating conclusion: the reef was again bleached, this time in an even larger area.
“It is the first time that we have seen heavily bleached reefs along the entire length of the reef, especially the coastal reefs,”
Recent aerial data from Professor Hughes and other scientists released on Monday show examples of overheating and damage along the reef, a 1,500-mile natural wonder. The survey represents an updated x-ray for a dying patient. The disease features are the treacherous white of the coral, which has lost its color and is visible from the air and water.
The mass bleaching indicates that corals are under great stress from the water around them. that got hotter and hotter
The world’s oceans, which absorb 93 percent of the heat trapped by the greenhouse gases that humans emit into the atmosphere through the burning of fossil fuels, warm up on average 40 percent faster than scientists estimated six years ago.
According to a recent study, 2019 was the hottest year in the world’s oceans.
With corals, the stress from these warmer waters usually leads to death. In the past, they may have recovered after the water has cooled, which can take 10 to 15 years. Now, however, a multitude of types of coral reefs around the world are experiencing mass extinctions.
About 30 percent of the corals on the Great Barrier Reef died after bleaching in 2016, the worst of five separate bleaching events since 1998.
This year’s bleach, which was documented by examining 1,036 sections of the reef, only seems to be in second place until 2016, according to Professor Hughes.
“We are surprised at the speed of this acceleration in bleaching,” he said. “We had a gap of 14 years between 2002 and 2016 and now, in five years, we have had three major events.”
The Great Barrier Reef isn’t quite dead – it’s big enough to carry swaths of healthy coral. But in many areas of the reef, corals that were once colorful are miles and miles white, brittle and broken or gray and covered with unsightly bacteria.
They are sensitive beings. Corals are tiny polyps that collect algae, convert sunlight into food, and form colorful colonies that form a limestone structure – a reef – on which to live. They thrive in warm water, but only up to a point: just two or three degrees Fahrenheit of excessive heating can kill the tiny creatures.
The temperatures in February during the summer in the southern hemisphere were far higher. It was the warmest month in which water temperatures were recorded near the reef. In some places, the season’s readings were above 5 degrees Fahrenheit above average.
Professor Hughes said that the heat waves of the past few years had a cumulative effect that drastically changed the composition of the reef.
The species most likely to bleach and die are staghorn corals and other root and branch corals with spaces in which many types of fish can swim and receive protection. The species that seem hearty enough to survive are usually dome-like corals, called brain corals, that play a role in protecting against coastal erosion, but are less valuable to fish and other wildlife.
“This is a transition from high diversity and many species to less diversity with less hard species,” said Professor Hughes.
The ripple effect could be significant. Hundreds of millions of people get their protein mainly from reef fish like coral trout, which has already been affected by the bleaching events on the Great Barrier Reef. Many scientists fear that the loss of this food supply could become a humanitarian crisis.
In the meantime, scientists who researched the coronavirus in March said they were sad and frustrated with what they had seen at sea.
Tracy Ainsworth, a marine biologist at the University of New South Wales, worked with a team on Heron Island in the southern part of the Great Barrier Reef, which was bleached for the first time this year.
The coral showed signs of stress in January, around the same time that the Australian bushfire crisis was at its peak.
After a period of cooler weather in February, overheating continued from the end of February to March. Scientists found dead corals in shallow reef habitats and bleached in deeper reef slopes that were believed to be better protected.
In many ways it was what Professor Ainsworth had expected.
“It is frustrating to still see reports of bleaching as a surprise,” she said.
Noting that scientists warned 20 years ago that coral reefs would be at risk if people didn’t tackle climate change, she added that many people who lived nearby believed in science at the time and now want to know why not more is done.
“We will continue to report declines and record changes on reefs and tell people what they already know about how corals die,” said Professor Ainsworth. “Isn’t it time to tell them more than that?”