The health of the Great Barrier Reef is widely thought to be an indicator for the state of the Earth’s marine ecosystems, and the announcement made Tuesday that the reef is currently experiencing the worst coral die-off in recorded history doesn’t bode well for the rest of our waters. The depressing conclusion was reached after evaluating data collected during more than 900 dives along the 1,400-mile reef.

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When coral is exposed to too much warm water, it dies, thus transforming from a vibrant display of colorful creatures to a white or greyish skeleton. Its light color is known as “coral bleaching,” and researchers are recording ever larger spans of the reef where this phenomenon is taking place. On Tuesday, Prof. Terry Hughes, director of the ARC Center of Excellence for Coral Reef Studies at James Cook University in Queensland, said on Tuesday that around two-thirds of the shallow-water coral on the reef’s 430-mile northern stretch is now dead, but the survival rates in the middle and southern parts of the reef are much better.

Related: No, the Great Barrier Reef isn’t dead – but it is damaged

“The good news is that in the south, only about 1 percent of the reef’s coral has died, and the mortality rate in the middle is about 6 percent,” Hughes said. “But in the north, mortality rates are very high, and in some places where coral has survived but it has weakened, the per capita predation rate has gone through the roof.”

Hughes noted that this is the third major bleaching event to hit the Great Barrier Reef, and that while some sections of the reef are still thriving, their fate remains uncertain. Increasing warming trends in ocean water currents pose higher and higher future threat to the remaining living coral, not to mention the other creatures living in and around the reef. In response to the issue, the Australian government is putting about $33.6 million into efforts to protect the reef, by improving water quality and reducing sediment runoff. Australian leaders may petition the United Nations to declare the Great Barrier Reef an “in danger” site, a move the international coalition has stopped short of in recent years.


Images via ARC Center of Excellence for Coral Reef Studies