English name

[Laminaria saccharina] with foliose red seaweeds and ascidians on sheltered tide-swept infralittoral rock

Description ( English )

Sheltered, tide-swept rock in south-western Britain tends to be restricted to estuarine conditions, where variable salinity and increased turbidity have a significant effect on the biota. Due to the turbidity of the water, the infralittoral zone is restricted to very shallow depths. Unlike the tide-swept channels in sealochs, which support a mixed kelp canopy, the rock in these estuaries is characterised by [Laminaria saccharina] alone, occurring in relatively low abundance (Frequent). The brown alga [Desmarestia ligulata] can occur in this biotope, though never dense, along with the non-native brown seaweed [Sargassum muticum]. Beneath the sparse kelp, cobbles and boulders, often surrounded by sediment, are encrusted by fauna and often a dense turf of red seaweed. The foliose red seaweeds associated with this biotope include [Callophyllis laciniata], [Nitophyllum punctatum], [Kallymenia reniformis], [Gracilaria gracilis], [Gymnogongrus crenulatus], [Hypoglossum hypoglossoides], [Rhodophyllis divaricata], [Chylocladia verticillata], [Cryptopleura ramosa] and [Erythroglossum laciniatum] as well as the filamentous [Ceramium nodulosum] and [Pterothamnion plumula]. Green seaweeds [Ulva lactuca], [Bryopsis plumosa] and [Cladophora] spp. may be locally abundant. The dominating faunal species vary from site to site but include sponges such as [Halichondria panicea], [Esperiopsis fucorum], [Dysidea fragilis] and [Hymeniacidon perleve] as well as ascidians, particularly [Dendrodoa grossularia] and [Morchellium argus], which can cover the rocks. Also present is the anthozoan [Anemonia viridis], the barnacle [Balanus crenatus] and the tube-building polychaete [Pomatoceros triqueter]. The hydroid [Plumularia setacea] can cover rocks and seaweed fronds Of the range of solitary ascidians found in the north-west, only [Ascidiella aspersa] tends also to be present in these south-western inlets. There is also a general absence of echinoderms. Where there is vertical rock present, it tends to support more fauna, including barnacles [Balanus crenatus], the ascidians [Clavelina lepadiformis] and [Botryllus schlosseri] and sometines the featherstar [Antedon bifida]. Where soft rock allows, such as the limestone in Plymouth Sound, rock-boring organisms such as [Polydora] sp. may be locally abundant. Sheltered, tide-swept rock is generally restricted to the narrows or tidal rapids of marine inlets. The clear tide-swept waters of Scottish sealochs are significantly different to the marine inlets of south-west Britain. This biotope deals with the latter. Situation: This biotope generally occurs on rocky outcrops interspersed by sediment areas. Where the rock extends into deeper water, beyond the limit of kelp, sponges and ascidians tend to dominate these sheltered, tide-swept circalittoral sites (A4.251); also [Alcyonium digitatum] with sponges and [Nemertesia antennina] (A4.131).

Source

Connor, D.W., Allen, J.H., Golding, N., Howell, K.L., Lieberknecht, L.M., Northen, K.O. & Reker, J.B. [edited ETC/BD] (2004)