Habitat point records from 1990 UMBSM North & South Uist and Benbecula sealochs survey

The Uist island chain in the Outer Hebrides is formed of Lewisian gneiss and is generaly low-lying with extensive and complex fresh and brackish water systems and a heavily indented eastern coastline. Five sealochs on the east coast, Lochs Boisdale, Skipport, Uiskevagh, Eport and Maddy, were surveyed during 1990 as part of the survey of Scottish sealochs. These were selected as being representative of the lochs present in the islands and share three major features. Facing east, they all have a limited exposure gradient. None is deep although Lochs Skipport and Maddy reach 40m in their entrances. Finally, as fiardic systems of varying degrees of complexity, they possess numerous islands and wide shallow basins in their upper reaches, connected to each other and to the main loch by narrow, often intertidal, channels with strong tidal streams. Several of these basins are brackish, Loch Obisary being a classic example; most are extremely sheltered. This combination of features means that the lochs possess a wide variety of habitats. Shellfish and salmon farms are established in all of the lochs surveyed and Ascophyllum nodosum is harvested from the shores for the alginate industry. Loch Maddy is an MCA and a part of the loch is included in the Loch an Duin SSSI. Loch Obisary, which is connected to Loch Eport by a sill 4 m above chart datum, is an SSSI and there are several others in the area. A considerable amount of survey work has been carried out in the Uists since McIntosh (1866) visited the islands, with notable littoral studies by Lewis (1957) and Powell et al. (1979) and several NCC-commissioned sublittoral surveys. Seventy sites were surveyed in total of which 62 were sublittoral and 8 littoral; 34 habitat/community typse were described. The distribution of these within each loch was broadly the same. The lochs were characterized by a variety of shallow sheltered habitats and communities, many of which were subject to tidal streams. There is a full transition from fresh and brackish to marine communities in these systems; only the marine component was investigated during this survey. Infralittoral bedrock communities ranged from rich Laminaria hyperborea forest at the entrances to cape-form L. saccharina forest in the most sheltered regions; the latter was unusually diverse. Deep bedrock, with Swiftia pallida and Diazona violacea, was restricted to the loch entrances. Sheltered circalittoral boulders were rare and were dominated by ascidians. The tide-swept Loch Eport entrance channel held a rich hydroid community not found elsewhere in the area. Sublittoral sediments varied from sandy mud with Virgularia mirabilis in the more seaward sections of the lochs to very soft, flocculent mud with dense populations of the rare holothurian Labidoplax media in the more sheltered basins. Tidal streasms of varying strengths flowed through shallow channels which had a corresponding range of communities from coarse sediments and maerl with Neopentadactyla mixta and Sabella pavonina to scoured bedrock. Particularly unusual were channels in upper Loch Maddy which supported extremely large laminarians and Halidrys siliquosa with a very rich sponge epiphyte community. Little littoral sediment was found, with most shores being bedrock or boulder and dominated by dense blankets of Ascophyllum nodosum. In the areas of strong tidal flow, rich under-boulder shore communities were found, characterised by ascidians and sponges. More exposed shores in the entrances supported barnacle and red algal communities with scattered fucoids. Eleven habitat/community types and 13 species have been provisionally assessed to be of Local, Regional, National or International importance. Records currently considered sensitive have been removed from this dataset.

Organization: Joint Nature Conservation Committee