Habitat point records from 1990 UMBSM Loch Etive survey

Loch Etive is a typical fjord, carved into grantie and metamorphic rocks by glaciers from the Rannoch Moor area. The steeply walled, deep upper basin is followed by a series of shallower basins and sills amongst low-lying lava hills towards the entrance. The ice left a bedrock bar across the outer sill which now forms the Falls of Lora, a spectacular tidal race. Rivers draining the glacier built an extensive plain of outwash gravel which partially dammed the loch entrance and formed the north bank of the loch near Connel. Two salmon farms and one trout farm have been established in the lower loch but the majority of mariculture is concentrated on mussel farming in the upper basin. Loch Etive is an Marine Consultation Area and there are 3 Sites of Special Scientific Interest adjoining the shoreline. Several marine biological studies have been carried out in the loch by workers based at the Dunstaffnage Marine Laboratory. Of most releveance is a series of papers by J. Gage and his co-workers based on surveys of the sediment infauna. Littoral studies were carried out by Powell et al. (1977). Forty-three sites were surveyed between the 15th and 22nd September 1990. These included 29 diving surveys, 3 anchor dredge samples and 11 littoral surveys; 25 habitat/community types have been described. Loch Etive is perhaps unique amongst Scottish sealochs for the extensive brackish conditions which influence the distritubtion of species. Freshwater draining into the loch from a vast catchment creates salinity gradients where salinities decrease towards the head and increase in deeper water. The surface layers are permanently brackish with salinities that vary considerably, but in deeper water, over approximately 15 m, conditions become more stable and salinities are higher. Consequently there is a noticeable changeover between shallow communities with brackish-tolerant species, such as Mytilus edulis, Carcinus meanas and Dendrodoa grossularia, which dominate the first few metres to more fully marine species in deeper water. However, certain stenohaline species, for example, the echinoderms Echinus esculentus and Psammechiuns miliaris were not found in the loch. Shallow substrata near the head of the loch were almost completely devoid of conspicuous flora and fauna. From a comparison made between this and an earlier visit it is clear that there is some turnover in species in the brackish layers controlled by fluctuations in the salinity (D.W.Connor and C.M.Howson, pers. com.). Brackish-tolerant and mainly opportunistic species colonize the shallow substrata when salinity levels increase and conditions stabilize. The deeper communities are affected to a lesser extent by brackish conditions. Large numbers of Neocrania anomala were found on deep bedrock along with Sarcodictyon roseum and Psolus sp.. The sediment communities in the deeper areas were reminiscent of those found in other fjordic sealochs, although diversity was somewhat reduced in all areas. There were prime examples of brackish tide-swept communities in the Falls of Lora and Kilmaronag Narrows. Much of the hard substrata in this area supported dense Laminaria hyperborea which was replaced in deeper water by a thick turf of Halichondria bowerbanki, Sertularia argentea and Alcyonidium diaphanum and there were also patches of bedrock with dense Flustra foliacea. Balanus crenatus was particularly abundant on the more scoured rocky substrata which included parts of the Bonawe Narrows. Seven habitat/community types and 11 species have been provisionally assessed to be of Local, Regional or National importance. Records currently considered sensitive have been removed from this dataset.

Organization: Joint Nature Conservation Committee