Report 411
Mid Irish Sea reefs habitat mapping report
Dalkin, M
Funding for this work has been provided by the Department for Food and Rural Affairs (DEFRA) Natural Environment Group Science Division (Contract No CRO 361).


The aim of this research contract was to improve understanding of the habitats and communities present in an area of the Irish Sea identified as potentially containing Annex I reef habitat according to the Habitats Directive. The potential Annex I reef area for this area was roughly delineated using British Geological Survey (BGS) 1:250,000 Seabed Sediment data (Graham., 2001). This area of habitat represented a number of polygons of quaternary sediment and rock according to the modified version of the Folk classification scheme used by BGS, and may consist of particles from am diameter up to cobbles and boulders.

To investigate and characterise the habitats and biotopes of an area of potential reef in the mid Irish Sea, new acoustic survey and biological survey was undertaken. The extent and distribution of the habitats and communities with the target area were mapped, and an assessment was made as to whether any of the habitats found fit within the interpretation of Annex I reef according to the Habitats Directive.


Survey cruises were undertaken in November 2006 and January 2007 onboard the University Marine Biological Station, Millport (UMBSM) Research Vessel Aora, with specialists from the National Oceanography Centre (NOC), ERT (Scotland) Ltd (ERT), UMBSM and Seatronics Ltd.  In discussion with JNCC, the survey area was split into three sections covering the northern, central and southern patches of potential reef identified by BGS.


In spite of bad winter weather and technical issues with camera equipment, the survey successfully collected acoustic data from target areas within the central Irish Sea and sufficient ground-truthing data to enable the classification and mapping of seabed habitats for the northern part of the survey area. Further acoustic data will be required to map the central survey area, and further ground‑truthing data will be required to map both the southern and central areas.


The surveyed depth ranged from approximately 60 to 155m. The shallowest depths were located on the western side of the southern survey area deepening gradually to the east and north. The deepest area was found in the south eastern corner of the northern survey area where a trough, approximately 2 km wide, deepened from a surrounding seabed of 90m to approximately 155m in its centre. There was a trend across the whole survey area of increasing depth from west to east, towards the deepest part of the Saint George’s Channel.


The sandiest sediments were found in the sand wave field in the north of the northern survey area in depths of less than 90m. The transition to coarser sandy sediments with an increased percentage of shell debris, pebbles and gravel followed an abrupt transition away from the sand wave field and this was reflected in both the bathymetry and backscatter data. The area of coarse sandy sediments covered the majority of the northern survey area at 90m. In deeper ground more stable mixed sediments became dominant. Sparse patches of small boulders were found at several sites.

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ISSN 0963 8901
Please cite as: Dalkin, M, (2008), Mid Irish Sea reefs habitat mapping report, JNCC Report 411, ISSN 0963 8901