|Researched by||Dr Harvey Tyler-Walters||Refereed by|
|EUNIS Code||EUNIS Name|
Dead maerl provides a substratum for the attachment of epiflora and epifauna, and a range of interstices for mobile epifauna, and shallow burrowing infauna. The variable and open structure of the maerl sediment can also provide good oxygenation at depth and allows many species to burrow deeply into the maerl substratum, while other deep burrowing species (e.g. mud shrimp) can also occur.
De Grave & Whitaker (1999) compared a dredged (extracted) maerl bed with one that been left ‘fallow’ for six months in Bantry Bay, Ireland. They noted that the dredged bed had significantly fewer molluscs than the fallow bed, but significantly more crustaceans and oligochaetes. Hall-Spencer & Moore (2000a, 2000b) examined the recovery of a maerl community after scallop dredging in previously un-dredged and dredged sites in Scotland. In comparison with control plots, mobile epibenthos returned within one month; fleshy macroalgae within six months; the abundance of the tube anemone Cerianthus lloydii was not significantly different after 14 months; other epifauna (e.g. Lanice conchilega and Ascidiella aspersa) returned after 1-2 years; but some of the larger sessile surface species (e.g. sponges, the plumose anemone Metridium senile, the horse mussel Modiolus modiolus and flame shell Limaria hians) exhibited lower abundances on dredged plots after four years. Deep burrowing species (mud shrimp, large bivalves e.g. Mya truncata and the gravel sea cucumber Neopentadactyla mixta) were not impacted and their abundance changed little over the four year period. Hall-Spencer et al. (2003) note that long lived (>10 years) species (e.g. the rayed artemis Dosinia exoleta) can occur at high abundances in maerl beds but that the sustainability of stocks are unknown at present. Hall-Spencer (2000a) noted that there was no significant difference between controls and experimentally dredged sites after 1-2 years at the sites previously subject to dredging.Overall, it appears that most of the maerl related community could develop within five years, although long-lived and/or large sessile species (e.g. bivalves, anemones, and sponges) would take longer.
|Recorded distribution in Britain and Ireland||Maerl beds (live and dead) have a patchy distribution around the coast of the British Isles. They are widespread around the west coast of Scotland, in the Western Isles, Orkney and Shetland but restricted to Milford Haven, the Pembrokeshire Islands and the Llyn Peninsula in Wales. Beds are rare in England, reported from Dorset, the Isles of Scilly and Lundy but with extensive beds in the Fal Estuary and mouth of the Helford River. Extensive beds occur on the north east coast of Northern Ireland, and along the west coasts of Ireland (e.g. Galway Bay). In Europe, maerl beds are found in the Mediterranean, and on the Atlantic coast from Norway and Denmark south to Portugal, Morocco and Mauritania on the African coast (Birkett et al. 1998). Few of the distributional records distinguish between ‘live’ and ‘dead’ beds. The map (above) only shows confirmed records of dead beds off the Isle of Bute and in Falmouth Bay.|
|Water clarity preferences|
|Limiting Nutrients||Data deficient|
|Other preferences||Not relevant|
The presence of ‘dead’ maerl beds is dependent of the prior growth and development of live maerl beds over decades or thousands of years. Therefore, dead maerl beds can only occur in areas that are presently, or were previously suitable for the growth of live maerl.
This MarLIN sensitivity assessment has been superseded by the MarESA approach to sensitivity assessment. MarLIN assessments used an approach that has now been modified to reflect the most recent conservation imperatives and terminology and are due to be updated by 2016/17.
|Community Importance||Species name||Common Name|
|UK Biodiversity Action Plan Priority|
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This review can be cited as:
Last Updated: 15/05/2013