Even the depths of the Great Barrier Reef are not sure of climate change

Even the darkest depths of Australia's world-renowned Great Barrier Reef may not be immune to the impacts of climate change, according to a New Zealand researcher.

Dr. Alice Rogers, of Victoria University, was part of an international team that studied in 2016 a mass-laundering event that wiped out about a third of Queensland's shallow water corals .

Coral bleaching, named because of the pale-white appearance of coral when it expels algae from its tissues, is caused by rising sea temperatures.

The new study, published in a major scientific journal Nature Communications, showed that if the deeper reefs suffered less damage, corals tens of meters below the surface still showed significant signs of whitening.

"We know little about the bleaching of temperature thresholds for corals living beyond the shallow and well-studied reef," said Rogers, of the Victoria School of Biological Sciences.

"We hope this study and other scientific work in this area will help us better understand the coral reef response to coral bleaching."

The lead author of the study, Dr. Pedro Frade of the Marine Science Center of Portugal, was alarmed by these new findings.

"It was a shock to see the impacts spread to these poorly lit reefs, as we hoped their depth could have provided protection against this devastating event," he said.

The team sent remotely operated vehicles and divers to inspect the reef.

Their findings showed that bleaching affected nearly a quarter of the corals at a depth of 40 meters, compared to about half of the corals at shallower depths.

During fading, the upwelling initially provided cooler conditions on the deep reef.

But when this rise stopped at the end of the summer, temperatures reached record levels, even at depth.

"Unfortunately, this research further highlights the vulnerability of the Great Barrier Reef," said co-author of the study, Professor Ove Hoegh-Guldberg, of the University of Queensland.

"We have already established that the role of refuge of deep reefs is usually limited by the limited overlap of species with the shallow reef," he said.

"However, this adds an additional limit by demonstrating that the deep reefs themselves are also affected by higher seawater temperatures."

The research team planned to study the recovery process following these bleaching episodes by examining differences in recovery from deeper and shallower reefs.