The coral reefs discovered some years ago in deep waters at the edge of the continental shelf may be much more extensive than originally thought. Another new bank of coral 64 km long and up to 350 m high has been located in 800 m-deep water in the Rockall Trough.
"We have no idea how old they are. They could be tens of thousands of years old," said Dr Anthony Grehan, a deep sea biologist at NUI Galway's Martin Ryan Marine Science Institute. The corals grow just two centimetres a year, so they must be quite old, but their future is uncertain unless efforts are made to protect this newly discovered marine habitat.
The reefs are formed by two species of coral, Lophelia pertusa and Madrepora oculata, and support a spectacular community of seafans or soft corals, sponges, starfish, spidercrabs and more, Dr Grehan said. "It is a very rich territory."
Most of the reef is made up of dead coral skeleton and only the top two metres or so is living coral. These marine animals eat other microscopic animals and build homes of carbonate minerals, hence the reefs.
While the reefs are large, they are easily damaged. They are found in much shallower water off Norway where destructive fishing practices have already reduced large tracts of reef to rubble, he said. "In Ireland, where the corals are deeper, perhaps we have some time to prevent an environmental catastrophe."
Dr Grehan discovered the new reefs earlier this month while on a mapping and sampling cruise aboard the Dutch RV Pelagia, organised by Dr Tjeerd van Weering, a leading sedimentologist from the Netherlands Institute for Sea Research. It included Irish and Dutch scientists and students from Germany and Belgium. His participation was supported by the Irish Observer Scheme of the Marine Institute.
High-resolution seismic mapping and sampling of the sea floor was carried out in the Porcupine Seabight and along the eastern and western margin of the Rockall Trough. Dr Grehan collected examples of the invertebrate fauna from all the locations sampled.
Deep water corals are much different from the more familiar tropical corals of the Pacific and the Caribbean, Dr Grehan explained. Tropical corals are much flatter and need light. They have established a symbiosis with marine algae and so they only grow in the shallows. Our corals grow in the dark and deep water cold and feed on other animals for survival.
Dr Grehan's study of retrieved corals uncovered an unusual association between a large marine worm, Eunice sp. and the coral. This predatory worm grows up to seven centimetres in length and has lethal jaws a centimetre across. It lives within a parchment-like tube tucked into the coral lattice, but its presence causes additional coral to form around the tube, protecting the soft worm tube in a tough outer skeleton provided by the coral.
The survey included remote core sampling at depths of up to 10 m into the sea floor sediments and box sampling to bring up sediments and living sections of coral complete with its local residents.
Studies of the coral will provide a wealth of information, both of the flora and fauna associated with the reefs but also about the chemical history of the oceans. Corals lock down isotopes of carbon and oxygen which can provide data about many deep sea chemical processes. Scientists are still struggling, however, with how these enormous reefs began; what triggered their slow but steady accumulation at such depths.
One theory suggests that the corals grow adjacent to places where much deeper hydrocarbon deposits seep through the seabed, Dr Grehan said. It could be that the coral can use these hydrocarbons or benefit from the presence of other organisms which use these substances.
Scientists are also interested in the biodiversity of the coral ecosystem, which may contain biocompounds for use in the biotechnology or pharmaceutical industries. The wormcoral interaction, for example, which causes enhanced calcium mineralisation, may result from a substance which if isolated could be used to encourage bone healing. "There are a lot of interactions that may suggest novel research in other areas," Dr Grehan said.