Habitat point records from 1981 James south Cornwall sublittoral survey

The principal aim of this survey was to record community and habitat information from the rocky sublittoral along the coast of Cornwall from Land's End to Nare Head (10 km north-east of Falmouth). The survey team comprised both biologically experienced and biologically 'naive' divers, education in marine life identification and survey techniques being a secondary aim of the expedition. Some sites in the survey area had been briefly examined during a joint UCS/NCC expedition in 1980 and descriptions of these are contained in the report of that expedition (Dipper, 1981). The south Cornish coast consists of a sequence of headlands seperating wide, shallow bays. The hard granite bedrock comprising much of the coast produces cliffs around the headlands, which drop more gently sublittorally, true vertical faces rarely being recorded over a large depth range although the massive, blocked structure of the granite makes smaller cliffs a feature of many sites. Outcrops of bedrock are commonly interspersed with areas of coarse shell sand, also present in the bottom of gullies. The large sweeping bays are predominantly sediment-bottomed with outcrops of either granite or of a finely bedded, slate-like rock with strata at a shallow angle to the horizontal (the sediment of these bays sometimes being finer). The 50 m depth contour generally runs to within 1.5 km of the major headlands, but does not penetrate the bays. Several of the many rock pinnacles present in the area were dived. Some of these rise to within 10 m of the surface and may drop to depths of over 40 m. With the prevailing wind south-westerly, from the open sea, south and west facing shores are very exposed or exposed to wave action, and north and east facing shores sheltered, few sites being very sheltered from wave action. Main tidal streams flow east-west, running principally between headlands with maximum current speeds of over 2.3 knots. Only subsidiary currents enter the bays. Additional water currents from river flow occur over the St Mawes' bank site. 19 sites were surveyed during the week, with as wide a range of exposure to tidal streams and wave action as was possible along the coast. Species lists were made, samples collected and habitats recorded. Profiles and brief descriptions of the seabed and dominant species at each site are provided in the report. The major sublittoral zone communities encountered are described, and comments on major species and groups of species noted. Some 'south-western' species are poorly represented in the results, particularly some of the conspicuous Anthozoa, which was surprising. Axinellid sponges were also scarce, as were the two Polymastia species and the bryozoan fauna was impoverished (similar to that of the west coast of Ireland). The area noted to be of greatest nature conservation interest was the Fal Estuary, particularly the St Mawes' Bank living maerl bed, which has been declared a Voluntary Marine Reserve since the survey took place. Carn Base and Porth Curno provide good examples of extremely exposed sublittoral habitats and the report suggests that further survey work should take place to the east of the Fal where reduced wave action and turbidity may give rise to some interesting communities. Two of the richest sites visited, were the Outer Bizzies and the Whelps and a wide range of habitats in a fairly small area was present at the Manacles. This site is much visited by sports divers (probably for the scenary and numerous wrecks) and the report suggests that this could be a potential base for a diver education site (e.g. a marine nature trail), a diving school being located nearby. The generally exposed nature of most of the survey area to waves and tidal streams and the precipitous coast both ensures that the communities present are not particularly suceptible to disturbance and that access to the area is limited. The main threat from divers is thought to be collection of marine curios such as Eunicella and Echinus (it is unknown whether this was the cause of low numbers of these species at many sites). The report also concludes that traditional fishing methods do not appear to pose a threat to the rocky littoral. Records currently considered sensitive have been removed from this dataset.

Organization: Joint Nature Conservation Committee