This survey was carried out to describe the range of sublittoral habitats and the communities of plants and animals present adjacent to the coast of the upper Bristol Channel. On the north side, from the east side of Swansea Bay to Llantwit Major and on the south side, at Porlock Bay, Minehead and Watchet. 16 sites were surveyed by diving within 43 km of coastline. All of the sites, except Gore Point on the west side of Porlock Bay, included a very small number of species of algae and animals compared to open coast areas of south-west Britain. Algae were only recorded above Chart Datum level. Animal communities were similar from site to site with stable rock surfaces at most sites dominated by Sabellaria spp. (mostly S. alveolata) and at some sites by Dendrodoa grossularia, Mytilus edulis or Polydora ciliata. A small variety of sponges, hydrozoans and bryozoans were also present in large amounts. Mobile or scoured substrata were characterised by Balanus crenatus and Pomatoceros triqueter. Moving west to east along the coast reveals a gradual reduction in the number of conspicuous species with a sharp reduction across Swansea Bay resulting in highly impoverished communities here. Along the majority of the coast studied, it is suggested that the circalittoral zone extended above the Chart Datum level and that the upward extent of the sublittoral zone, based on the presence of sublittoral algae, extended to about 2.5 m above Chart Datum compared to about 1 m on the open coast. The presence of extensive areas of sand and of sand in suspension during strong tidal flow, is considered to be important in the development of large colonies of Sabellaria alveolata. This and previous surveys emphasise the importance of S. alveolata as a dominant species. Records currently considered sensitive have been removed from this dataset.
