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 |
| Siltation |
Fishing: benthic trawling |
Low |
Although towed gear may not directly cross circalittoral
faunal turf biotopes (see above), the activities of dredging and trawling on nearby level
bottoms with softer sediments could have effects on neighbouring communities. Towed gear
results in the suspension of fine sediment (Jones 1992), which can affect the efficiency
of filter feeding (Sherk 1971; Morton 1977) and in exposed situations can cause scour (see
‘Habitat requirements’). |
| Hydrocarbon contamination |
Uses: boats/shipping (oil spills) |
Low |
Untreated oil is not a risk to circalittoral communities as
it is concentrated mainly at the surface. If oil is treated by dispersant the resulting
emulsion will penetrate the water column, especially under the influence of turbulence. |
| Changes in nutrient levels |
Waste: sewage discharge |
Low |
The primary effect of increased nutrient levels is to
stimulate algal growth, both of benthic macroalgae and microscopic phytoplankton. Since by
definition circalittoral faunal turf communities are essentially animal dominated, the
effects of eutrophication will be indirect. Changes in the phytoplankton are more likely
to produce impacts. Increased phytoplankton densities will change the food supply for the
predominantly filter-feeding communities. Blooms of toxic algae may affect survival of
circalittoral rock communities, perhaps particularly in their planktonic larval stages. |
| Abrasion |
Fishing: benthic trawling |
Intermediate |
Towed gear is potentially the most destructive impact, and
has been the subject of the most intensive study (MacDonald et al. 1996). However,
most circalittoral rock biotopes will not generally be threatened since the generally
steep and rocky substrata are unsuitable for both trawls and dredges. However there are
types of towed gear designed for rocky areas – the rockhopper otter trawl, and the
Newhaven scallop dredge and these could pose a risk to circalittoral rock communities on
gently-sloping or level rock. |
| |
Fishing: potting/creeling |
Low |
Static gear is deployed regularly on rocky grounds, either in
the form of pots or creels, or as bottom set gill or trammel nets. Whilst the potential
for damage is lower per unit deployment compared to towed gear, there is a risk of
cumulative damage to sensitive species if use is intensive. Damage could be caused during
the setting of pots or nets and their associated ground lines and anchors, and by their
movement over the bottom during rough weather and during recovery. |
| |
Fishing; angling |
Low |
Rod and line angling is the least likely activity to produce
incidental damage from the fishing itself – the main risk is damage from the
anchoring of the angling boats. Frequent anchoring in areas which often experience strong
tidal flow is an obvious problem. |
