Habitat

James et al. (2010) provides an excellent introduction to the habitats found in Eastern English Channel Region. The following text is from that report. The Sussex IFCA through its research over the coming months and years will be, with partners, building upon this work.

'Chalk reef habitats in the District (the eastern Channel which represent 75% of all chalk reefs in Europe) support a wide range of characteristic species, some of which are predominantly found on or in this type of substrate. A number of species are capable of boring into the rock and these tend to dominate the associated subtidal communities. These species include bivalve piddocks, polychaete worms and sponges. The biotope dominated by piddocks is often the most widespread of the biotopes which occur on these reefs but is scarce in Britain as a whole.

The hard rock habitats off the Sussex Coast are often colonised by keelworms and by barnacles Balanus spp. In slightly deeper water, the hydroids and the foliose bryozoan Flustra fascialis (formerly F. foliacea) can be found. Mobile species commonly found on rock are the whelk Buccinum undatum, the topshell Gibbula cineraria and the netted dogwhelk Hinia reticulata, together with hermit crabs Pagurus spp. and the swimming crabs Liocarcinus spp. Where there is foliose algal cover there is a greater range of mobile fauna, including the spider crabs Macropodia rostrata and Pisa tetraodon. In even deeper water, several species of sponge are likely to be conspicuous, including Esperiopsis fucorum and Dysidea fragilis. Ross coral Pentapora fascialis, a bryozoan is often conspicuous on bedrock outcrops.

Areas of nearshore mixed sediments tend to be formed of variable amounts of sand, gravel and cobble, often mixed with dead shells and shell gravel. In areas where these mixed sediments are stable, settlement and subsequent growth of a rich variety of plant and animal species occurs. The anemones Anemonia viridis and Urticina felina are typical of gravel areas, with Cerianthus lloydii also frequently encountered. The slipper limpet Crepidula fornicata is commonly associated with gravel and its shells can form the main hard substrate in areas of soft sediments. Gravel habitats found in deeper offshore areas (>30 metres), tend to be less affected by natural disturbance than those closer inshore. As a result, these areas tend to support diverse marine fauna which may include a wide range of anemones, polychaete worms, bivalves and amphipods and both mobile and sessile epifauna.

Sand sediments are found in regions of moderate to strong tidal currents where they are able to settle but finer particles cannot. In such situations, the sand is often coarse and clean with little mud, but with occasional shell fragments present. Mobile sands tend to be characterised by robust and sometimes impoverished faunas, typically venerid bivalves, amphipods, polychaete worms and heart urchins. Sand banks can also occur in the area, particularly to the eastern end of the Channel. They provide important nursery grounds for young commercial fish species, including plaice Pleuronectes platessa, cod Gadus morhua and sole Solea solea.

Generally, the muddy and silty sediments of the Solent and Chichester Harbour contain chains of slipper limpets Crepidula fornicata, which provide attachment for other organisms such as hydroids (e.g., Kirchenpaueria pinnata and Hydrallmania falcata) and sponges (e.g.Halichondria spp. and Suberites spp.). A number of small crab species, such as Pisidia longicornis, Macropodia rostrata and Pagurus bernhardus, are found in cover provided by the slipper limpet shell epifauna. Polychaete worms, bivalve molluscs such as cockles, and brittlestars can also be numerically dominant in mud habitats where hard biogenic substrates (i.e. Crepidula shells) are absent.

Some organisms found in the eastern Channel can aggregate in sufficient numbers to influence significantly the number and variety of other organisms around them (e.g. kelp and seagrass in the photic zone, maerl, the common mussel Mytilus edulis, slipper limpets Crepidula fornicata and the Ross worm Sabellaria spp.). Particular biogenic habitats are often associated with specific broad habitats, for example, maerl is usually associated with gravel, seagrass beds with sand, mussels with mixed sediments, though reefs formed by animals such as the Ross worm Sabellaria spp. can be associated with a range of habitats such as gravel, pebbles and cobbles, and bedrock.'

James, J W C, Pearce, B, Coggan, R A, Arnott, S H L, Clark, R, Plim, J F, Pinnion, J, Barrio Frójan, C,Gardiner, J P, Morando, A, Baggaley, P A, Scott, G, Bigourdan,N. 2010. The South Coast RegionalEnvironmental Characterisation. British Geological Survey Open Report OR/09/51. 249 pp.