Deep water could be reef’s salvation

Thriving deep water coral populations could hold the key to saving the Great Barrier Reef’s degraded surface coral.

While surface coral is struggling due to the effects of storms, coral bleaching and the damaging crown-of-thorns starfish, a deep water survey has discovered large and healthy coral populations directly below those damaged communities.

At depths below 30m, the early findings of the Catlin Seaview Survey show coral is largely unaffected by the problems faced nearer the surface, a result that has shocked scientists involved in the project.

“The Holmes and Flinders Reefs in the Coral Sea are renowned for having been badly damaged,” said University of Queensland’s Dr Pim Bongaerts, who is 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 70-80 metres down, there are significant coral populations.”

A recent report by the Australian Institute of Marine Science says the Great Barrier Reef has lost half its coral cover in the past 27 years.

But survey members say the discovery of thriving populations in largely unexplored deep water regions suggest that finding is based on an incomplete picture of the reef.

Dr Bongaerts said the discovery of wide areas of healthy deep reef raises the possibility that they could provide a refuge for corals that are under stress in the shallow reef.

“This mesophotic layer, just beneath shallow reefs, could provide coral recruits for the upper levels of the reef,” he said.

“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.”