Small-scale variation within a Modiolus modiolus (Mollusca: Bivalvia) reef in the Irish Sea: I. seabed mapping and reef morphology

Charles Lindenbaum, James Bennell, Ivor Rees, Donald McClean, William Cook, A Wheeler, William Sanderson

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    43 Citations (Scopus)


    Surveys by digital side-scan sonar, RoxAnnTM acoustic ground discrimination systems, multibeam echosounder and a sub-bottom profiling system showed that a Modiolus modiolus reef, in the Irish Sea off Pen Llyˆn, north-west Wales, had a distinctive morphology and acoustic characteristics. The extent of the reef could therefore be determined and the benthic structure reliably mapped. The biogenic reef is in an area with moderately strong tidal currents and overlays lag gravel and cobbles with patchy sand veneers. The mussels form an undulating surface, orientated perpendicular to the current, with an average wavelength of 11.7 m and amplitude of 0.24 m that is significantly different from the surrounding seabed. Reef deposits reach a thickness of 1 m on top of the underlying lag gravels. The characteristic reef surface morphology helps distinguish the reef from the surrounding seabed on side-scan sonar and multibeam echosounder records and the undulations create the spatial complexity that influences the small-scale distribution of the associated epifauna, and infauna, reported in papers II and III of this series. The M. modiolus reef was recorded in the same location 40 y ago and has probably persisted there for over 150 y. Monitoring implications are discussed.
    Original languageEnglish
    Pages (from-to)133-141
    Number of pages9
    JournalJournal of the Marine Biological Association of the United Kingdom
    Issue number1
    Publication statusPublished - Feb 2008


    • Modiolus
    • biogenic reef
    • bioherm
    • sonar
    • Irish Sea
    • monitoring
    • SAC
    • conservation management


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