Mass bleaching event on Great Barrier Reef damaged deeper corals

The mass bleaching event -- that wiped out 30 per cent of shallow-water corals on Australia's iconic Great Barrier Reef in 2016 -- may have also caused damage in deeper waters, scientists say.

Although deep reefs are often considered a refuge from thermal anomalies, the research, published in the journal Nature Communications, highlights limitations to this role and argues that both shallow and deep reefs are under threat of mass bleaching events.

"During the bleaching event, cold-water upwelling initially provided cooler conditions on the deep reef," said Pim Bongaerts, from the California Academy of Sciences in the US.

"However, when this upwelling stopped towards the end of summer, temperatures rose to record-high levels even at depth," said Bongaerts.

The researchers found bleached coral colonies down to depths of 131 feet beneath the ocean's surface.

"It was a shock to see that the impacts extended to these dimly lit reefs, as we were hoping their depth may have provided protection from this devastating event," said