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Marine Habitat Classification

Description of biotope or habitat type

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   Filamentous red seaweeds, sponges and Balanus crenatus on tide-swept variable-salinity infralittoral rock

Physical habitat description

Salinity Variable (18-35 ppt)
Wave exposure Extremely sheltered
Tidal streams Moderately strong (1-3 kn)
Substratum Bedrock; boulders
Zone Infralittoral
Depth Band 0-5 m
Other Features Heavily silted / turbid water

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.FilRVS Filamentous red seaweeds, sponges and <I>Balanus crenatus</I> on tide-swept variable-salinity 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.


Tide-swept infralittoral rock subject to variable salinity and turbid waters occurs in the mid to upper reaches of the rias of south-west Britain, where riverine freshwater input reduces the salinity. Very shallow rock under these conditions is characterised by a covering of filamentous red seaweed such as Callithamnion spp., Antithamnion spp., Ceramium spp., Griffithsia devoniensis, Pterothamnion plumula and Vertebrata fucoides, as well as the filamentous green seaweed Cladophora spp. Foliose red seaweeds such as Hypoglossum hypoglossoides, Cryptopleura ramosa and Erythroglossum laciniatum commonly occur, as does the foliose green seaweed Ulva lactuca. Although Saccharina latissima is often present it is usually in very low abundance (Occasional). The fluctuating salinity limits the number of species able to exist in this habitat. The animal community is dominated by the sponges Halichondria panicea and Hymeniacidon perlevis and the barnacle Balanus crenatus. The ascidians Clavelina lepadiformis and Dendrodoa grossularia can be locally abundant at some sites. The crab Carcinus maenas is usually present, as is the mussel Mytilus edulis. The bryozoan Crisularia plumosa is sometimes present. Where vertical rock is present, the seaweeds Ceramium nodulosum, P. plumula, C. ramosa, H. hypoglossoides and E. laciniatum are typically found.


This biotope is usually found amidst sediment or rock and as such there is no defined zonation of the surrounding biotopes. Shallow sediments nearby may support seagrass beds (Zostera spp.) or infaunal-dominated sediments (SS.SCS.ICS). Nearby, deeper tide-swept rock may support circalittoral communities dominated by sponges, hydroids and ascidians on stable rock (CuSpH.As) or dense bryozoans on mixed substrata (SpNemAdia & FluHocu).

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Hypoglossum hypoglossoides 18 Frequent 81-100%
Pterothamnion plumula 14 Frequent 61-80%
Erythroglossum laciniatum 8 Frequent 41-60%
Halichondria panicea 8 Common 61-80%
Callithamnion 6 Frequent 41-60%
Carcinus maenas 4 Occasional 41-60%
Hymeniacidon perlevis 4 Frequent 41-60%
Balanus crenatus 3 Occasional 61-80%
Vertebrata fucoides 3 Occasional 21-40%
Antithamnion 2 Occasional 21-40%
Cladophora 2 Occasional 21-40%
Griffithsia devoniensis 2 Frequent 21-40%
Mytilus edulis 2 Occasional 21-40%
Ulva lactuca 2 Occasional 21-40%
Crisularia plumosa 1 Occasional 21-40%
Ceramium nodulosum 1 Occasional 21-40%
Clavelina lepadiformis 1 Frequent 21-40%
Cryptopleura ramosa 1 Common 21-40%
Dendrodoa grossularia 1 Occasional 21-40%
Saccharina latissima 1 Occasional 21-40%

Similar biotopes or habitat types

This biotope occurs at similar conditions as IR.MIR.KT.FilRVS. The species diversity is also similar between the to biotopes, but IR.LIR.K.SlatT have a higher abundance of the kelp S. latissima (Common) and of the ascidian Dendrodoa grossularia (Abundant). IR.MIR.KT.FilRVS have a higher abundance of the sponge H. panicea.

Classification history of this biotope or habitat type

Classification version Code
1996 (6.95) SIR.Lsac.FiR

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