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). Conversely suspended sediment is vital for
some species. Sabellaria spinulosa requires suspended sand grains in order to form
its tubes and will therefore only occur in very turbid areas where sand is placed in
suspension by water movement. |
| 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 |
Moderately exposed circalittoral rock biotopes occur in open
coast situations, usually in or close to waters of considerable depth. They are therefore
not generally near sources of discharge of organic pollutants and even if they were they
would be considered as Higher Natural Dispersion Areas, and therefore apparently at
little risk. The primary effect of eutrophication 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. |
| Removal of non-target species |
Fishing: potting/creeling |
Low |
The traditional harvesting activity in circalittoral areas
has been for crabs, lobsters and crayfish by potting and by bottom-set tangle or gill
nets. The latter also target. |
| |
|
|
fish as a by-catch. The obvious effect is the reduction in
numbers of the target species, which are an important component of these communities. The
reduction in these large predatory species will also have effects on the rest of the
community, but these have not been evaluated in British waters. Diving may also damage
circalittoral rock communities by the collection of animals either for food, or as
souvenirs |
