Sensitivity to human activities

Activities listed are those which influence, or are likely to influence this habitat and which are assessed in the UK marine SAC project review. The sensitivity rank may require amendment in the light of new information becoming available.

Sensitivity to: Human activity Rank Comments
Substratum change Waste: spoil dumping


Deposition of capital dredging such as barge loads of boulder clay which will initially settle as a mass, will almost certainly smother the patch it lands on. From such spoil mounds the material usually disperses, but there are no case histories to indicate rates of sediment accretion that Modiolus clumps can keep up with. In a Modiolus bed off the Humber long-term changes in contaminant loads associated with spoil disposal were detectable in the shells of Modiolus modiolus. While this indicates survival of the mussels within a dispersal zone around the disposal ground, information on the loss of condition is not available.
Changes in temperature Climate change/global warming


Modiolus modiolus is a northern species, and the fact that dense aggregations seem to reach their southerly limit around British shores suggests a possible susceptibility to a long-term rise in summer water temperatures.
Hydrocarbon contamination Uses:boats/

shipping (oil spills)


As Modiolus modiolus are filter feeders, depending on suspended particles in the water column for food, they tend to be very sensitive to oil pollution (Dethlefsen, 1978). Lees & Driskell (1981) suggested that suspension feeders such as Modiolus would be highly sensitive to the effects of an acute spill.
Abrasion Fishing: benthic trawling


Scallop and queen scallop dredging has been implicated in the dramatic reduction in density and extent of the widespread and often dense areas of Modiolus bed, which was described by Jones (1951) off the south east of the Isle of Man. Magorrian et al. (1995) observed damage to Modiolus clumps in Strangford Lough owing to queen scallop trawling. The scallops and queens are fished using heavy metal dredges, usually with large prominent metal teeth along the leading edge. This fishery practice has also been found to damage many of the epibenthic species found in association with Modiolus beds. (Hill et al. 1997). It is unlikely that scallop or queen fishing would be very viable over very dense reef areas, and it has therefore been assumed that many years of fishing on adjacent areas have to some extent damaged the edges of the denser beds.

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