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 rock
(see above), the activities of dredging and trawling on nearby level bottoms with
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 most of the faunal turf communities are filter
feeders. Effects can include abrasion and clogging of gills, impaired respiration,
clogging of filter mechanisms, and reduced feeding and pumping rates. |
| Hydrocarbon contamination |
Uses: boats/shipping (oil spills) |
Low |
Untreated oil is not a risk to circalittoral communites as it
is concentrated mainly at the surface. If oil is treated by dispersant the resulting
emulsion will penetrate the water column. |
| Changes in nutrient levels |
Waste: sewage discharge |
Intermediate |
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. One effect of eutrophication will be the way it
influences the growth of benthic macroalgae, which may influence the level of the boundary
between the infralittoral and the circlittoral. Improved macroalgal growth might be
expected to lower this boundary, but at the same time increased phytoplankton density will
reduce light penetration. Changes in the phytoplankton are more likely to produce impacts.
Increased phytoplankton densities will change the food supply for the predominantly
filter-feeding faunal turf communities. Blooms of toxic algae may affect survival of
circalittoral faunal turf communities, perhaps particularly in their planktonic larval
stages. Algal blooms are often considered a near-surface phenomenon, and are more likely
to pose a threat in sheltered conditions. |
| Abrasion |
Fishing: benthic trawling |
Low |
Towed gear is potentially the most destructive impact, and
has been the subject of 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 faunal turf 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. Qualitative
observations of pots and creels being dropped and hauled in Devon and Scotland showed that
potting did not appear to have any immediate effect on several species that had previously
been thought to be sensitive to impact (Eno et al 1996). 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. |
