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Marine Habitat Classification

Description of biotope or habitat type

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   Saccharina latissima with foliose red seaweeds and ascidians on sheltered tide-swept infralittoral rock

Physical habitat description

Salinity Full (30-35 ppt), Variable (18-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum Boulders, bedrock and gravel
Zone Infralittoral
Depth Band 0-5 m
Other Features

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat IR.MIR.KT.SlatT <I>Saccharina latissima</I> with foliose red seaweeds and ascidians on sheltered tide-swept infralittoral rock

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.


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 Saccharina latissima 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 Metacallophyllis 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, Amphilectus fucorum, Dysidea fragilis and Hymeniacidon perlevis 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 Spirobranchus 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.


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 (CuSpH); also Alcyonium digitatum with sponges and Nemertesia antennina (ByErSp).

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Saccharina latissima 23 Frequent 81-100%
Ulva lactuca 5 Frequent 41-60%
Ceramium nodulosum 4 Frequent 41-60%
Dendrodoa grossularia 4 Abundant 41-60%
Cryptopleura ramosa 3 Frequent 21-40%
Halichondria panicea 3 Occasional 41-60%
Hymeniacidon perlevis 3 Frequent 41-60%
Hypoglossum hypoglossoides 3 Occasional 41-60%
Nitophyllum punctatum 3 Occasional 41-60%
Rhodophyllis divaricata 3 Occasional 41-60%
Balanus crenatus 2 Occasional 21-40%
Metacallophyllis laciniata 2 Occasional 21-40%
Kallymenia reniformis 2 Occasional 21-40%
Plumularia setacea 2 Occasional 21-40%
Spirobranchus triqueter 2 Occasional 21-40%
Sargassum muticum 2 Occasional 21-40%
Anemonia viridis 1 Occasional 21-40%
Bryopsis plumosa 1 Occasional 21-40%
Chylocladia verticillata 1 Rare 21-40%
Desmarestia ligulata 1 Rare 21-40%
Dysidea fragilis 1 Occasional 21-40%
Gracilaria gracilis 1 Occasional 21-40%
Morchellium argus 1 Frequent 21-40%
Pterothamnion plumula 1 Occasional 21-40%

Similar biotopes or habitat types

Not applicable or unknown.

Classification history of this biotope or habitat type

Classification version Code
2015 (15.03) IR.MIR.KT.LsacT
1997 (97.06) SIR.K.Lsac.T (part)

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