Deep coral reefs are not safe from the threats posed by warming waters caused by climate change, a study published by international marine scientists on Wednesday has found.
The scientists said they had evidence to suggest the 2016 bleaching event at Australia's Great Barrier Reef also affected corals living in deep, dimly-lit water.
The finding, published in the Nature Communications journal, is bad news for the resilience and long-term health of the natural wonder that is home to millions of marine lifeforms.
The Reef, off Australia's north-eastern coast, is the world's largest coral system - covering an area larger than Italy - and is one of most biodiverse ecosystems on the planet.
But in recent years, it has suffered from a crown-of-thorns starfish epidemic, sedimentation, degradation of water quality, ocean acidification, and massive back-to-back bleaching events in 2016-17 that scientists said "cooked" parts of the Reef.
Deep reefs are often considered "a refuge from thermal anomalies," caused by global ocean warming.
But the new research highlighted limitations to this view and argued that both shallow and deep reefs were threatened by mass bleaching events, the scientists said.
The scientists used remotely operated vehicles to deploy sensors down to 100 metres, followed by surveys by a team of divers during the height of bleaching across several sites on the northern Reef.
The study found the bleaching affected almost a quarter of coral up to 40 metres below the surface due to increasing temperatures.
At the shallower depth, nearly half the corals had been severely affected after 2016 bleaching event.
