SYDNEY, April 9 (Xinhua) -- Though some deeper parts of the Great Barrier Reef may be shielded from harmful heatwaves for now, the protection will be lost if global warming deepens, a new study has warned.

Researchers from Australia's University of Queensland and Britain's University of Exeter examined how changing temperatures would influence the vast areas of deeper and mesophotic reefs at 30 to 50 meters, rather than focusing on the impacts of sea surface temperatures on the shallowest corals.

According to their findings published in the journal Proceedings of the National Academy of Sciences, some deep-water refugia were identified in the Great Barrier Reef where thermal stratification helps protect those mesophotic species from dangerous heat.

"We found separation between warm buoyant surface water and cooler deeper water can insulate reefs from surface heatwaves, but this protection will be lost if global warming exceeds three degrees Celsius above pre-industrial levels," Peter Mumby, co-author of the study and professor at the University of Queensland, said in a statement on Tuesday.

The latest weekly report from the Great Barrier Reef Marine Park Authority showed that of over 1,000 surveyed reefs, half recorded high or very high levels of coral bleaching, and less than 10 percent experienced extreme levels.

Mumby flagged coral bleaching as "a dramatic sign of the impact humans are having on the planet," which is increasingly observed at greater depths.

"Our study offers both hope and a warning -- hope that some reefs are resilient to current levels of climate change, and a warning that this resilience has its limits," he said.

The study revealed that a global warming of three degrees Celsius would push mesophotic temperatures in the Great Barrier Reef past 30 degrees Celsius -- a recognized threshold for coral mortality.

"There is so much to learn about deeper, tropical coral reefs, especially as we cannot assume that their depth provides a refuge from the consequences of rising global carbon emissions," said Paul Halloran, another co-author and associate professor from the University of Exeter.

"By targeting management of these threats, hopefully, some healthy reefs can be maintained," he added. Enditem

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