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 |
Intermediate |
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 |
Intermediate |
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) |
Intermediate |
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 |
High |
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. |
