Deep-water coral found off the South West continental shelf Published: 29 June, 2007
RV Celtic Explorer
A TEAM of Irish and UK Marine scientists discovered the cold-water coral, Lophelia pertusa, in unexplored deep-sea canyons 400 km south of Cork on the edge of the European continental shelf during a recent MESH (Mapping European Seabed Habitats) survey on the Irish national RV Celtic Explorer.
Deep-water camera equipment was used to capture images of the sea floor in water up to 1 km deep, where pressure is 100 times greater than surface pressure. Cameras also captured evidence of the impact of fishing on the mound forming coral, as trawl marks in the seabed and discarded fishing nets and ropes were encountered on a number of occasions.
The survey, carried out by the Marine Institute, the British Geological Survey (BGS), the University of Plymouth and led by the Joint Nature Conservation Committee (JNCC), provided a test for using the INTERREG IIIB funded MESH projects Guide to Marine Habitat Mapping for seabed surveys in deep offshore waters.
Little was known of the biology or geology of the canyons, on the cusp of UK, French and Irish territorial waters, beyond a few historical records of cold-water corals. One of the reasons for carrying out the survey was to find out if the canyons supported large cold-water coral reefs, or steep rocky reefs, which could be considered for protection under the European Unions Habitat Directive.
The survey, between June 4 and 17 centered over two canyons on the edge of the continental shelf plateau at 200m depth, down to 1,000m, covering an area greater than 850 km2, more than 120,000 football pitches. Scientists investigated the morphological and geophysical structure of the canyon systems and mapped the distribution and extent of the habitats using high-resolution multibeam sonar to create 3D maps. The BGSs sub bottom profiling sparker, capable of penetrating up to 500m below the canyons surface, was used on the R.V. Celtic Explorer for the first time, to examine the thickness of sediment layers and the structure of the underlying bedrock.
Some parts of canyons show erosional features and others depositional, with indications of both downward and upward currents across the survey area, resulting in the interesting geological structures and ecology of the area, according to Heather Stewart of BGS.
Forty-four video transects were made, lowering the camera on a winch wire to over 1,000m deep and towing it along slowly, to distinguish biological communities in the canyons. “Much more of the seabed than expected, consisted of fine, muddy sands,” added Ms Stewart. “We found hard substrata (rock and boulders) and corals in only a few areas along the steeper edges of the canyons.” Ripples in the sediment show current directions. Sea cucumbers (Holothurians), squat lobster (Munida rugosa), numerous anemone and several starfish species, sea pens, shell debris and fish species were also encountered.
In Ireland, techniques for marine habitat mapping have been developed within the Irish National Seabed Survey Programme and within INFOMAR – the successor project to map inshore waters, said Marine Institute Chief Executive Dr. Peter Heffernan speaking about the recent discoveries.
The Marine Institute has been deeply involved with both of these projects, along with a number of partners including the Geological Survey of Ireland. Seabed habitat mapping is an important policy support tool in Sea Change the Marine Knowledge and Information Strategy 2007 2013.
Analysis of data will continue through to January 2008. Maps showing the distribution of the different seabed habitats found will be produced, and cold water coral or rock reef habitats will be considered, where appropriate, for designation as Special Areas of Conservation under the EU Habitats Directive. Findings are also being analysed as PhD research being undertaken at Plymouth University.
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