Australian reef study shows 'cooked' coral killed off by heat

Large parts of Australia's Great Barrier Reef were literally cooked to death in a recent marine heatwave, according to a new scientific study.

More than 1000km of the northernmost part of the 2300km long Barrier Reef on Australia's northeast coast died off due to warmer waters in 2016 and 2017, Australian scientists found.

"They didn't die slowly of starvation, they died directly of heat stress. They cooked because the temperatures were so extreme," said Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Townsville.

Hughes and his colleagues conducted aerial surveys of the entire reef, as well as detailed in-water surveys, at 63 locations along its 2300km length, and combined it with data from satellite monitoring. The study was published yesterday in the journal Nature.

Water temperatures along the reef rose 1C above the average caused by a combination of climate change and the El Nino weather cycle.

"When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die. Averaged across the whole Great Barrier Reef, we lost 30 per cent of the corals in the nine-month period between March and November 2016," Hughes said.

Warmer waters killed off close to half the corals in shallow water across the northern two thirds of the Great Barrier Reef due to continuous bleaching in the past two years.

The scientists found the bleaching and subsequent death of coral is now affecting the central region of the reef.

"But that still leaves a billion or so corals alive, and on average, they are tougher than the ones that died. We need to focus urgently on protecting the glass that's still half full, by helping these survivors to recover," said Hughes.

"The Great Barrier Reef is certainly threatened by climate change, but it is not doomed if we deal very quickly with greenhouse gas emissions.

"Our study shows that coral reefs are already shifting radically in response to unprecedented heatwaves.

"The Great Barrier Reef of today, or certainly in 10 or 20 years' time from now, will be a very different system from the reef that we've been studying for the last 30 or 40 years," he said.

- dpa