Using deep-sea diving techniques, researchers have found healthy corals lying deep below Australia's extensively damaged reefs.

The Catlin Seaview Survey conducted off the coast of northern Queensland, using a robot capable of diving deeper than any human diver, found habitats of healthy coral at depths of 30 metres to 120 metres, right underneath extensively damaged the Great Barrier Reef.

Lead researcher Pim Bongaerts, from the University of Queensland's global change institute, said, "Some of the shallow areas of the reefs we've been diving on have been completely devastated by cyclones, but as soon as we dive to depths of 40m and below, the areas are almost completely untouched."

Previously, researchers had very little knowledge about the deep reefs, largely because they had been using typical techniques like scuba diving, which is capable of gathering information to depths of up to 30 metres.

But the new study suggests that deeper waters may provide a sort of refuge for corals, and may also be a key to restore damaged reefs.

The researchers say that corals lying in the upper and lower waters are part of the same population. They may have moved to deep waters, which could be a key part of regeneration of the damaged upper reefs.

A separate report by the Australian Institute of Marine Science recently revealed that coral population in the shallow part of Australia's Great Barrier Reef has slipped by more than 50 per cent over the past twenty-seven years, and 48 per cent of that damage was caused by storms.