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Scientists have discovered corals living at extreme depths on the Great Barrier Reef.
The Catlin Seaview Survey team, which is mapping reefs threatened by climate change around the world, found corals living 125 metres below the surface of the ocean in late December. They were the deepest ever found on the reef.
The extreme depth is more than four times that of the shallow reef corals, which are usually about 30m down.
Dr Pim Bongaert, who led the expedition to the outer Ribbon Reefs, says the discovery of coral where sunlight is so scarce is mind-blowing.
"It's intriguing. When we began our survey, we were amazed to see significant coral communities at depths of around 60 metres," he said in a statement.
"It is truly mind-blowing to see reef coral at more than twice that depth and four times deeper than most scuba divers can reach.
"There are coral communities on the Great Barrier Reef existing at considerably greater depths than we could ever have imagined."
The survey also collected samples of large Staghorn Acropora corals living at a depth of 73m, the deepest they have been seen.
Dr Bongaert said the team would analyse the specimens to find out what enabled reef corals to survive at such extreme depths.
"These discoveries show just how little we really know about the reef and how much more is yet to be discovered," he said.