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
Siltation Fishing: benthic trawling


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)


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


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


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/



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.

Next Section                     References