North-West Anglesey Reef


Dense brittlestar bed on boulders, cobbles and pebbles composed mainly of the common brittlestar (Ophiothrix fragilis) with some Ophiocomina nigra © JNCC, CCW, UCCDahlia anemone (Urticina felina) and common starfish (Asterias rubens) © JNCC, CCW, UCCBoulders and cobbles with dead man’s fingers (Alcyonium digitatum), encrusting bryozoan (Pomatoceros sp.) and hydroids (Abietinaria abietina) © JNCC, CCW, UCC


The aim of this study was to investigate an area identified as containing potential Annex I bedrock, stony or biogenic reef.


To the north and north-west of Anglesey four areas were identified by the British Geological Survey under a separate contract as potentially containing bedrock or stony reef, covering an area of approximately 140 km2. It was also anticipated that areas of biogenic reef may be found within the survey areas, due to historic records of Modiolus modiolus in the vicinity.


In the summer of 2005, the opportunity arose for JNCC to collaborate with partners of the INTERREG funded HABMAP project. Between 9th and 14th August 2005, JNCC, in collaboration with the Countryside Council for Wales and University College Cork, surveyed these four areas from the RV Celtic Voyager. High resolution multibeam bathymetry and backscatter data were obtained for all four survey areas. Seventeen grab samples were obtained in three of the four survey areas. Twenty-nine video tows were obtained from all four survey areas.


Multibeam imagery from North-West Anglesey © JNCC, CCW, UCC


The results from the current study suggest that the seabed in this study area was broadly characterised by complex topography and mixed sediment mosaics, which were home to tide-swept benthic communities.


Analysis of the infaunal communities sampled using a grab showed that all samples belonged to the same circaliottoral coarse sediment biotope, SS.SCS.CCS.MedLumVen. A range of biological communities were also determined from the video analysis. Some were typical of boulder areas subjected to moderate tidal streams and were typified by faunal crusts. In one of the survey areas, very high densities of the brittlestar Ophiothrix fragilis, along with lower numbers of Ophiocomina nigra, were present, blanketing the underlying rocky substrate. Gravelly substrates were also common throughout the survey areas, supporting biological communities that did not easily match existing biotopes within the Marine Habitat Classification for Britain and Ireland (version 04.05).


Annex I reef was observed in patches throughout the four study areas. Where Annex I reef was found, it was comprised of boulders and cobbles. Along video tows, reef habitat tended to alternate with more gravelly areas of non-reef habitat. No biogenic reefs (formed by either Modiolus modiolus or Sabellaria spinulsoa) were encountered through the survey, although some juvenile Modiolus modiolus were recovered in grab samples.


Although Annex I reef was found in a number of locations, indicating that this could be an area of conservation interest, further work is required to compare the results of the current study with other known areas of reef within the Irish Sea, with respect to the SAC site selection criteria.


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Further Reading

  • Blyth-Skyrme, V., Lindenbaum, C., Verling, E., Van Landeghem, K., Robinson, K., Mackie, A., Darbyshire, T. 2008. Broad-scale biotope mapping of potential reefs in the Irish Sea (north-west of Anglesey). JNCC Report 423.


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