Shallow sublittoral ecosystems in the Inner Hebrides

SynopsisRapid advances in scientific SCUBA diving have provided a means of investigating the previously difficult ground of the shallow sublittoral. Dhing surveys of the Inner Hebridean islands have been promoted and coordinated by the Nature Conservancy Council (NCC) and the Underwater Conservation Society (UCS) to provide appropriate data for reviewing the marine nature conservation importance of the area. Although the surveys have been extensive rather than intensive, and many areas have yet to be investigated, a short preliminary descriptive account of the communities of the shallow seas of the Inner Hebrides is presented in this paper.The classification and description of sublittoral habitats is essentially related to the substratum type and the influence of water movement and light penetration. Although the diversity of habitat types is probably less for the Inner Hebrides than either the outer islands or the mainland, the larger islands show a range of exposure from the sheltered mud of sea lochs to wave- and tide-exposed bedrock. The juxtaposition of three marine biogeographical regions around the British Isles is reflected in the biota of the Inner Hebrides. In addition to the typical ‘Scottish’ sublittoral biota there is an associated assemblage of south-western species, and a number of northern species at their south-western limit. In many areas the diversity of the biota is reduced by the intense grazing of the sea urchin Echinus esculentus, a notably Scottish phenomenon.