Doyle Rice

USA TODAY

One of the world’s treasures, the Great Barrier Reef, just suffered from its worst coral die-off ever recorded, Australian scientists announced Monday.

Stress from unusually warm ocean water heated by man-made climate change and the natural El Niño climate pattern caused the die-off. "The coral was cooked,” Terry Hughes, director of the Australian Research Council Centre of Excellence for Coral Reef Studies, told the BBC.

At more than 1,400 miles long, Australia's Great Barrier Reef is the world's largest coral reef and the planet's biggest structure made by living organisms. In the northernmost section of the reef, which had been considered the most "pristine," some 67% of the coral died.

The good news, scientists said, was that central and southern sections of the reef fared far better, with "only" 6% and 1% of the coral dead, respectively.

Coral reefs result from the work of little polyps, creatures only a few millimeters long, budded on top of one another. Over centuries, the shells of these creatures combine to form the exotic shapes of coral reefs. Tiny differences in the anatomy of each polyp species affect the shape of their shells and produce the exotic shapes of each reef.

The vibrant colors that draw thousands of tourists to the Great Barrier Reef each year come from algae that live in the corals tissue. When water temperatures become too high, coral becomes stressed and expels the algae, which leave the coral a bleached white color.

Mass coral bleaching is a new phenomenon and was never observed before the 1980s as global warming ramped up.

Besides their beauty, reefs shelter land from storms, and are also a habitat for myriads of species.

"Coral reefs are therefore the most biologically diverse ecosystems of the planet, and provide a number of ecosystem services that hundreds of millions of people rely on," said Greg Torda, also of the Centre, in an e-mail to USA TODAY.

"These include provisioning (fishing, other types of harvesting, for pharmaceuticals, for example), coastal protection, aesthetic and cultural values – to name a few. If corals are lost, so are all the services they provide to humans; and so are all the species that directly or indirectly rely on them."

Tourism on the Great Barrier Reef employs 70,000 people, and generates $5 billion (Australian) in income each year, the Centre said in a statement.

The good news is that much of the coral survived this bleaching event. But looking to the future, mass coral bleaching on the Great Barrier Reef will likely be an annual phenomenon within a decade, Torda said.

If all the coral died on the reef, “it would be among the largest mass extinction events in history,” said Torda.