Habitat point records from 1988 MNCR Rockall survey

Rockall and its associated reefs are situated 306 km west of St Kilda on the Rockall Plateau, and are isolated from the shallow waters around Britain by the Rockall Trough, which reaches depths of over 3000 m. Marine biologically they are of particular interest as the marine communities are at the extreme wave exposed end of our currently perceived wave exposure scales, and their isolation prevents an effective barrier for colonisation by organisms with pelagic larvae. This survey was carried out in June 1988, in unusually calm weather. The survey team was based aboard the Department of Agriculture and Fisheries for Scotland's Fishery Protection Vessel 'Norna'. Two littoral sites were surveyed on Rockall, and ten sublittoral sites on Rockall and the associated reefs. Previous studies on the marine biology of Rockall have suggested that its small size, isolation and extreme wave exposure have reduced the diversity of the littoral and sublittoral species present. The results of this survey suggest that this view still holds true and that the general impoverishment reflects the isolation and general wave exposure of the site. However, in the littoral, rock crevices and hollows under the encrusting red algae were found to harbour more animal species than the rock surfaces previously surveyed. Although it is generally the case that animals recorded from the littoral of Rockall do not have a pelagic dispersal phase, a small group of the barnacle Verruca stroemia were recorded on the rock, and the molluscs Hiatella and Modiolus within the algal crusts during this survey, indicating that settlement from a planktonic dispersal phase must be possible. The sublittoral of Rockall was richer than previously reported, although many algal species present at St Kilda were not recorded. Of the species recorded, some were found much deeper than expected, such as the brown alga Alaria esculenta which extended down to 33 m. The kelps Laminaria digitata and L.hyperborea were absent from Rockall and Hasselwood Rock, although they were recorded from Helen's Reef. This may be due to the greater availability of upward facing rock surfaces on Helen's Reef, which present an easier surface for colonisation than the predominantly vertical surfaces recorded around Rockall. This synopsis has been extracted from the field report. The final survey report has not yet been produced.