A recent survey of the Coral Sea and Great Barrier Reef has found coral flourishing in deep waters, a stark contrast to the shallower reefs that have seen a drastic decline over the last few decades.
The healthy coral populations were discovered to be below 30 meters — beyond the usual reach of most scuba divers — and even found at depths of 80 meters, according to the Catlin Seaview Survey.
“The Holmes and Flinders Reefs in the Coral Sea are renowned for having been badly damaged, said Pim Bongaerts, of the University of Queensland’s Global Change Institute, who was leading the deep reef survey.
“Yet we have found their deep reef zone is hardly disturbed at all. In fact the most striking thing is the abundance of coral on the deep reef. What has blown me away is to see that even 70 to 80 meters down, there are significant coral populations.”
Earlier this month a report, by the Australian Institute of Marine Science (AIMS) and the University of Wollongong, revealed that the Great Barrier Reef had lost half its coral cover in the last 27 years.
Researchers say most of the damage to the shallower coral was wrought in recent years by a succession of powerful cyclones. Other threats that are hindering its ability to recover include the crown-of-thorns starfish, or COTS, a native species which feeds on coral, and coral bleaching that occurs when water becomes too warm.
The deep reef survey team used remote operated vehicles able to reach depths of 100 meters, giving scientists a new view of hitherto unexplored reefs.
“It is surprising in this day and age, that below some of the most well-known reefs, which are so popular with divers, there is an almost entirely unexplored world and as a result an enormous amount of science to be done,” said Bongaerts.
So far the team has completed four of its ten planned surveys at areas along the length of the 2,300 kilometer-long reef system and outlying atolls.
Bongaerts believes that the deep-water reefs might be able to help the shallower ones recover, as they have been seen to live in both depths of water.
“At the moment we know little about the extent of larval movements between the shallow and deep reef, but we are seeing species that exist in both zones,” he said.
“There are clear differences we’re observing. Corals are much flatter, more plate-like than the branching and domed shapes seen nearer the surface. This is the corals responding to the reduced light conditions and spreading out to maximize their exposure to light. So far below the surface, the light is blue because all other parts of the spectrum have been filtered out. It is a monochrome world until you turn on strong lights to reveal amazing, beautiful, fantastic colors.”