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Australia's Great Barrier Reef is heralded for its biodiversity: The colorful clusters of coral and wisps of islands stretch 1,400 miles, home to white and orange clown fish, the blacktip shark, humpback whales and hundreds of other species.

But those clear blue-green waters are also changing faster than previously thought, according to a new study in the journal Nature, worrying scientists who say the survival of the Great Barrier Reef and other ecosystems like it is crucial for the planet.

Healthy coral off Lizard Island in the Great Barrier Reef. The Ocean Agency/XL Catlin Seaview Survey

"There's huge trouble in paradise," said Craig Downs, a biologist who studies dying coral in Hawaii.

At the Great Barrier Reef — considered one of the Earth's largest living structures — about half of the coral died in 2016 and 2017 because of record extreme heat, a result of climate change driven by greenhouse gas emissions, the researchers found.

Historically, coral deaths were at a smaller 5 percent to 10 percent.

Other research has estimated that 90 percent of the world's corals could be dead as soon as 2050.

Australia's weather bureau said 2017 was the country's third-hottest year on record, and the scorching temperatures came despite the lack of an El Niño system that normally brings warmer weather.

Scientists are concerned that the colonies of coral that make up the Great Barrier Reef have been damaged to a point where they won't bounce back. If corals remain in too-warm water they turn white — a process known as bleaching — and can potentially die.

A severely bleached branching coral sits amid minimally bleached boulder coral. Gergely Torda / ARC Centre of Excellence for Coral Reef Studies

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"It's quite challenging to witness the severity of this bleaching — it's the worst we've ever seen," Terry Hughes, director of a government-funded center for coral reef studies at James Cook University in Australia and the lead author of the study, told Nature.

He said that while some types of coral died, others survived — indicating the make up of the reef is undergoing a remarkable transformation.

"Losing a lot of corals has a broader ecological impact: species that eat the corals lose their food source; fish that would hide in the corals become more susceptible to predation from sharks," Hughes added.