Australia's Great Barrier Reef has lost half its corals in 25 years

Australia's Great Barrier Reef has lost over half of its coral populations in the past three decades because of ocean warming, a study published in the journal Proceedings of the Royal Society B published Wednesday finds.

Why it matters: The World Heritage-listed underwater ecosystem is a haven for biodiversity, with some 4,000 species of fish, 700 species of coral and "thousands of other species of plants and animals," per the nonprofit Coral Reef Alliance. It spans some 1,400 miles — making it the largest coral reef ecosystem in the world.

What they did: Researchers from the ARC Centre of Excellence for Coral Reef Studies (CoralCoE), in Queensland, Australia, assessed coral communities and their colony size along the length of the Great Barrier Reef from 1995 to 2017.

What they found: Researchers discovered that climate change is driving an increase in the frequency of reef disturbances, such as marine heatwaves. Nearly every coral species has declined since the comprehensive research began.

• "We found the number of small, medium and large corals on the Great Barrier Reef has declined by more than 50% since the 1990s," said study co-author Professor Terry Hughes, from CoralCoE, in a statement.
• Researchers uncovered steeper deteriorations of coral colonies in the northern and central Great Barrier Reef after mass coral bleaching events in 2016 and 2017. The southern part of the reef was also exposed to record temperatures earlier this year.

"The decline occurred in both shallow and deeper water, and across virtually all species — but especially in branching and table-shaped corals. These were the worst affected by record breaking temperatures that triggered mass bleaching in 2016 and 2017."

What they're saying: Bob Richmond, director of the Kewalo Marine Laboratory at the University of Hawai'i at Manoa, who's extensively researched reefs, told the Washington Post the Australian research shows "demographic changes are occurring on a regional scale ... on reef slopes that make it difficult for coral reefs to persist over time."

• "These bleaching events are just hammering these reefs. ... The problem is it's an accelerated loss. It's hard to have a crystal ball and say a date," Richmond said.
• "Scientists are always trying to be careful, but if we don't act meaningfully in the next five years, we will not have vital and vibrant coral reefs as a legacy for future generations."

The bottom line: "The loss of these corals means a loss of habitat, which in turn diminishes fish abundance and the productivity of coral reef fisheries," the study notes.

• "[W]e must sharply decrease greenhouse gas emissions ASAP," the researchers concluded.

Go deeper: Global warming is pushing the Great Barrier Reef to the brink