Climate change during the last 25 years has destroyed half the corals in the Great Barrier Reef off the northeast coast of Australia, according to a scientific study published Wednesday by the British journal Proceedings of the Royal Society.
The study on the world’s largest living organism points to a vast decline in all shapes and sizes of corals — a living species of marine invertebrates — since the mid-1990s.
Branching corals and table corals, which have flat horizontal surfaces, have been the hardest hit, nearly vanishing from the far northern reaches of the reef, according to CBS News.
“They’re typically depleted by (up to) 80 or 90 percent compared to 25 years ago,” said Terry Hughes, a co-author of the report and a professor at James Cook University. “They make the nooks and crannies that fish and other creatures depend on, so losing big three-dimensional corals changes the broader ecosystem.”
The vast underwater ecosystem is a global treasure, recognized as a World Heritage site because of its invaluable scientific and environmental value.
Over time, a dramatic rise in ocean temperatures has damaged the health of the 1,400-mile reef, which reaps an estimated $4 billion a year in tourism revenue for the Australian economy, CBS reported.
The warmer water has also accelerated the frequency that corals release algae, which has depleted the size of the reef and sucked away its vibrant colors.
This naturally occurring phenomenon — known as bleaching — was first seen on the reef in 1998, which at the time was the warmest year on record. Bleaching events happened again in 2016 and 2017, prompting the Australian government to devaluate the reef’s future health.
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“A vibrant coral population has millions of small, baby corals, as well as many large ones — the big mamas who produce most of the larvae,” the study’s lead author Andy Dietzel, also of James Cook University, said.
“Its resilience is compromised compared to the past, because there are fewer babies and fewer large breeding adults.”
For the first time, the bleaching has been documented along wide swaths of the reef’s southern expanse, according to CBS.
Since 1995, several cyclones have severely damaged the reef along with two outbreaks of crown-of-thorns starfish, which eat coral.
Scientists expect a significant die-off of the reef unless nations recommit to policies under the 2016 Paris Agreement on climate change that would help reduce average global temperatures in the coming years. Even then, Hughes said, “we don’t think they’ll rebuild into the mix of species that we’ve known historically.”
“It takes about a decade for a half-decent recovery for the fastest-growing species, so the chances of us getting decades between the future sixth, seventh and eighth bleaching events is close to zero because temperatures are because going up and up and up,” Hughes said.
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