Habitat point records from 1977 SWBSS Lundy sublittoral survey

The present survey was carried out in order to describe the range and extent of the sublittoral habitats present around Lundy. The survey was also intended to test methods for quick survey and recording. The survey was carried out by a team of six university divers. Survey stations were located at depth intervals of 5 m mostly along Ordnance Survey Grid Line positions from 0 to 40 m. Check lists were used to record the habitats present and the main rock cover organisms. Descriptive surveys were carried out by swim lines, drift dives and with a towed sledge. Sediment samples were collected at some sites. The sites surveyed were distributed all around Lundy and extended to 1 km offshore. 206 stations were surveyed and descriptive surveys carried out at 13 locations. Supplementary information was obtained from 58 locations described by other workers. A wide variety of habitats were present around Lundy. Off the west coast there was a gradual slope of bedrock to a depth of about 35 - 40 m, 1 km offshore, followed by a sand or gravel plain. In pockets between the rocks small boulders, stones, gravel and mud were present. Along most of the south coast there was a gradual rock slope extending to up to 1 km offshore. However, extensive areas of sand were present in some places and, off the south-east of Lundy, the seabed was of broken slates. Sand and gravel was present as pockets amongst the rocks, but mud was recorded at only one station as 'minor'. The north coast was generally similar to the south coast but off Seals Rock, rock surfaces dropped very steeply to about 30 m. Off much of the east coast, a bedrock and boulder slope extended to about 9 m, was followed by a band of mud covered sediment several hundred metres wide and continued offshore as a plain of muddy gravel. Sand was present in the Landing Bay and offshore on the south part of the east coast. Steeply sloping rock surfaces were present at the Knoll Pins and at Gannets Rock. In many areas, rock surfaces were very broken with pinnacles and canyons present. A dense forest of Laminaria hyperborea was present to a depth of about 7 m around most of Lundy but only to about 5 m on parts of the east coast. The kelp forest was followed by a kelp park amongst dense foliaceous algae which extended to about 10 m. Around most of Lundy, the stable rock substrates below the zone of algal domination were characterised by dense bryozoa/hydrozoa populations with a wide variety of sponges and anthozoans present. Off the south-east corner in depths below 20 m, beds of brittle stars were present. The mud covered sediments off the east coast were characterised by burrows of Goneplax rhomboides and Cepola rubescens whilst the muddy gravel areas were characterised by sparse populations of Pecten maximus. The distribution of substrates around Lundy clearly reflects the predominant conditions of water movement. Thus, the extensive areas of rock present off the west, north and south coasts are kept mainly clear of sediment by strong wave action and tidal streams. The sheltered east coast is a deposition area. The extent of kelp and foliaceous algae around Lundy is accounted for largely by the turbidity of the water but also by the presence of silt on rocks and by grazing pressure on the east coast. The dense cover of bryozoa and hydrozoa around most of the island on rock is accounted for by the favourable conditions of water movement which brings food and maintains rock clear of silt. The location of sites provided a good basis for mapping and included all of the main habitats. However, the distance between depth stations was often considerable on gently sloping seabed and supplementary stations were required to map the limits of some features. Drift dives and the towed sledge provided a considerable amount of useful information. In future surveys of extensive areas of flat seabed, remote methods of observation might provide a better basis for mapping than the use of diving. Records currently considered sensitive have been removed from this dataset.

Organization: Joint Nature Conservation Committee