In the following sections, ‘status and monitoring value’ summarize the extent of our current knowledge of the biotope complex in each SAC, and make a provisional assessment of the relative importance of the site from a conservation perspective. ‘Potential management concerns’ and ‘Recommended action’ are self-explanatory.

Loch nam Madadh probably contains good examples of the biotopes CMU.SpMeg, CMU.SpMeg.Fun and CMU.VirOph. The nationally rare Funiculina quadrangularis and Pachycerianthus multiplicatus are present (Entec, 1996), species found in very few other candidate or possible SACs. The spatial extent of the sediment biotopes within the loch system has been mapped, but we still lack data on sea pen abundance, and details of the species composition of the burrowing megafauna.

The density of human habitation in the loch area is low. Lochmaddy township discharges some sewage into the loch. There are a number of sites leased for salmon or shellfish cultivation, all in the outer islands and channels of the loch system (Howson, 1991). A small amount of fuel oil contamination and general marine litter is likely to arise from the ferry terminal and other boating activities in Lochmaddy Harbour. There is also small-scale creeling for Nephrops. The generally low intensity of human activities in the area suggests that there are unlikely to be any significant impacts on the biotope complex at present, although the effects of any future expansion of salmon farming in the loch system should be monitored. Loch nam Madadh is a fiardic sea loch, with maximum depths at its entrance (Howson, 1991). The finer muds with Pennatula, Funiculina and burrowing megafauna are found in this outer, deep region which continues into the open sea. In this relatively open and well-flushed area they are likely to be less vulnerable to the impacts of aquaculture than similar biotopes located in the more enclosed upper reaches of fiordic sea lochs.

A systematic survey using towed video or ROV should be carried out to give more precise information on biotope distributions and species abundances. Only at the outer edge of the loch system are water depths of over 30 m reached, so that supplementary diver observations or transect counts would be possible throughout almost all of the areas of interest.

The state of knowledge of the biotope complex in this area essentially mirrors that described above for Loch nam Madadh. Sediment biotopes are extensive, with records of both sea pens (Virgularia mirabilis) and burrowing megafauna, but details of community composition and species abundances are lacking.

Small discharges of sewage effluent take place from housing in the Arisaig area, but the local population density is so low that the effects of this will be minimal (Howson, 1990). Sites have been leased for salmon and shellfish farming in Loch Ailort, Loch Ceann Traigh and Loch Moidart, and there are further experimental aquaculture-related activities in and around the Sea Fish Industry Authority research station at Ardtoe. The effects of aquaculture are likely to be limited to areas of restricted water circulation in upper Loch Ailort and the north channel of Loch Moidart. The megafaunally-burrowed muds recorded by Davis & Hall-Spencer (1996) are in areas relatively open to the sea and unlikely to be affected by the current levels of aquaculture in the sea lochs.

There is some local creel fishing for Nephrops in the Sound of Arisaig area. It is not known if trawling is pursued this close inshore, but any occurrence of this should be monitored for its potential effects on the mud biotope along the Open Coast.

A quantitative survey by towed video would be highly desirable to provide more information on the communities present in the area. The megafaunally-burrowed muds in Loch Ceann Traigh and in the Open Coast area (Davies & Hall-Spencer, 1996) are at depths (30 - 60 m) beyond effective diving range.

The biological diversity and recognised conservation importance of Strangford Lough have led to its major biotopes being mapped in some detail (Erwin, 1977; Magorrian et al., 1995). As for Loch nam Madadh and the Sound of Arisaig, our knowledge of the local sea pen/megafauna biotope is limited to its spatial extent and the presence of a few conspicuous species (Virgularia mirabilis, Nephrops norvegicus, Goneplax rhomboides). An accurate assessment of the representativeness (and hence conservation importance) of this community relative to others of its type awaits a more detailed quantitative survey.

Strangford Lough supports a much larger human population than either of the Scottish SACs discussed above. The largest town is Newtownards on the northern shore. Other villages contribute to a total lough-side population of about 60,000. There are seven main sewage outfalls discharging effluent after various degrees of treatment (Service, 1993). The finer sediments have an organic carbon content mostly in the range 2 - 5% (one station with a value of 6.8% was found). The sediments therefore have a high organic content, but are within the range recorded for naturally-enriched sea loch sediments. Service (1993) found high chromium concentrations in the sediment at some stations, associated with tannery effluent discharged through the sewage outfall at Killyleagh. Past discharges of chromium exceeded 10 tonnes per year, but this quantity has since been reduced 10-fold. No strong spatial trends were found in the distribution of other heavy metals in the lough. Magorrian et al. (1995) found high densities of Nephrops norvegicus on the mud grounds in the central part of the lough, suggesting that megafaunal communities have not been adversely affected by effluent discharges, but it would be advisable to have more information on the dispersal of particulate organic matter in relation to biotope distributions. Strangford Lough also contains extensive and very dense beds of epifaunal suspension-feeders (brittlestars Ophiothrix fragilis, and horse mussels Modiolus modiolus), and it is possible that the filtering activities of these animals may play a part in ameliorating the effects of effluent discharges into the lough.

There is a small Nephrops fishery within Strangford Lough, mainly carried out by potting (R. Briggs, personal communication). This is unlikely to cause any significant damage to the biotopes of interest.

It would be desirable to have more detailed information on the species composition and abundance of the soft-sediment communities in Strangford Lough. The mud grounds in the lough are mostly at depths below 30 m (Magorrian et al., 1995), so that a video survey would be required. The mud substrata with high Nephrops densities are rather patchy, and broken by areas of harder, rougher ground, but Magorrian et al. (1995) were able to successfully employ a towed camera system in the lough.

Unlike the three localities discussed above, Cardigan Bay has been proposed as a candidate marine SAC not on the basis of its benthic communities but because of its importance to an Annex II marine mammal species, the bottlenose dolphin, Tursiops truncatus. The available information shows that sediments burrowed by thalassinidean crustaceans do occur in the bay, but appear to occupy a fairly small proportion of its area. While it would clearly be useful to have more detailed information on community composition, it is unlikely that Cardigan Bay supports any of the biotopes or species of conservation importance, as defined in this report. No measures specifically targeted on sediment biotopes are therefore recommended. Measures undertaken to maintain the quality of the area as a dolphin habitat (eg. reducing human pollutant inputs of all kinds) will also contribute to the preservation of the bay’s benthic biotopes.

Information on the current distribution of burrowing megafauna in Plymouth Sound is limited, but past records suggest that a high diversity of species may be present. The sound is not an important locality for sea pens, although Virgularia mirabilis appears to be sparsely present.

Substantial amounts of sewage enter Plymouth Sound, either directly, or via discharges into the estuaries of the Plym and Tamar. Much of this is untreated (Devon Wildlife Trust, 1993). There are no major industrial effluents entering the sound, but a considerable amount of oil, antifoulants and litter must originate from shipping and recreational boats in the area. There is little commercial fishing within the sound. Periodic dredging is carried out to keep navigational channels open.

Overall, the human influence on Plymouth Sound is so extensive and of such long standing that its existing biological communities are probably robust and able to maintain themselves without the need for active conservation measures. Any sensitive species particularly vulnerable to man-made environmental changes would probably have disappeared long ago. The local examples of the biotope complex are therefore not considered to be under any threat, or to require any active management.

The sediment biotopes within Plymouth Sound probably do not include species of high conservation importance, but an updating of the rather fragmentary information on their character would be useful. Most of the sedimentary substrata within the sound are in relatively shallow water, so that diving could be used to supplement any observations made using towed video or ROV.

Sea pens and burrowing megafauna appear to be absent from the Fleet proper, but are recorded within Portland Harbour. The harbour lies outside the proposed boundaries of the SAC, but the extension of these should be considered, as the community within Portland Harbour is of a type uncommon in southern Britain, and contains several species of regional or national conservation importance. Dyrynda’s (1984) observation of numerous Virgularia mirabilis is interesting, as this species is generally uncommon in southern Britain. Other unusual records included Cepola rubescens. and the anemone Scolanthus callimorphus, which is known only from one other locality in the British Isles (western Ireland).

The range of human influences on Portland Harbour must be comparable to that in the northern section of Plymouth Sound, and leads to the same general conclusions about the robustness of the species and communities there. However, given the apparent distinctiveness of the Portland examples, it would be desirable to have a more detailed assessment of current and projected human impacts on the sedimentary biotopes here.

An updating of Dyrynda’s (1984) survey of Portland Harbour would be valuable. Information on current status could be gained most easily by diving, as the water depth in the outer harbour is only about 10 m.

Information on the biotope complex in this candidate SAC is limited to a description of the spatial extent of the silty sand substratum, one record of Virgularia mirabilis and some observations of unspecified megafaunal burrows.

The benthic biotopes in the area must experience some sewage input from the coastal communities, but this is unlikely to be of much significance along this open, current-swept coastline. Some trawling for Nephrops norvegicus occurs in this area (J. Kinnear, personal communication). However, with so little information on the biological community it is not possible to assess its conservation importance or assess the significance of human impacts upon it.

A detailed biological survey using towed video is highly desirable. The areas inferred to support sea pens and megafauna are well below the depth range accessible to divers.

Other candidate or possible SACs

Of the localities designated as candidate or possible SACs, this loch system contains the richest and best-characterized examples of the ‘Sea pens and burrowing megafauna’ biotope complex (Connor, 1989). Virgularia mirabilis occurs throughout all three lochs, but the richest community appears to exist in deep muds at the head of Loch Duich, including forests of Funiculina quadrangularis and a large population of Pachycerianthus multiplicatus. Burrowing megafauna include Nephrops norvegicus, Callianassa subterranea, Calocaris macandreae and Lesueurigobius friesii. At the time of Connor’s (1989) report there appeared to be little threat to the biotope complex, although he noted that leases for salmon farms had been granted in Lochs Alsh and Duich. An expansion of fish farming in Loch Duich might have some adverse effects on the benthic communities due to the highly-enclosed situation of the loch. Monitoring the effects of any new aquaculture developments should therefore be the highest managment priority if the site is designated as an SAC.

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