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Marine Habitat Classification

Description of biotope or habitat type

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   Dense foliose red seaweeds on silty moderately exposed infralittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Moderately strong (1-3 kn)
Substratum Bedrock; boulders & cobbles
Zone Infralittoral
Depth Band 5-10 m, 10-20 m
Other Features In turbid conditions

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.KR.XFoR Dense foliose red seaweeds on silty moderately exposed 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.


Upward-facing surfaces of shallow, infralittoral bedrock and boulders in areas of turbid water dominated by dense red seaweeds, with the notable absence of kelp. The stable rock, which can be cobbles or boulders but is more typically bedrock, is usually silted. Individual species of foliose red seaweeds such as Plocamium cartilagineum or Calliblepharis ciliata often dominate. Other red seaweeds likely to be present include Phyllophora crispa, Rhodymenia holmesii, Halurus flosculosus, Cryptopleura ramosa, Hypoglossum hypoglossoides, Heterosiphonia plumosa and coralline crusts. The brown seaweed Dictyota dichotoma is sometimes present, although never abundant. This biotope does not generally occur below kelp park but rather occurs on shallow, silted rock on which kelp would normally grow in less turbid conditions. The fauna can be variable but is generally typified by the presence of silt-tolerant animals such as encrusting sponges, particularly Dysidea fragilis and Halichondria panicea, the hydroid Tubularia indivisa, bryozoan crusts and scattered Sabellaria spinulosa and Balanus crenatus. In the summer months the seaweeds can become heavily encrusted with the bryozoan Electra pilosa and the ascidian Molgula manhattensis which can also form dense mats on the rock. The polychaete Lanice conchilega can be present, where sandy and muddy patches occur. Where this biotope occurs on chalk bedrock, such as off the Sussex coast, the piddock Pholas dactylus is often found bored into the rock. This biotope is recorded from the English Channel, off Kent, Sussex and the Isle of Wight. Please notice that individual sites of this biotope can vary significantly in the species composition.


This biotope generally occurs on discrete bedrock outcrops surrounded by areas of mixed sediment or mobile sand. Off Sussex, it occurs on the horizontal chalk bedrock forming the tops of cliffs (2-3m in height).

Temporal variation

The seaweeds die back in late autumn and summer leaving, silted, coralline-encrusted rock with a sparse fauna of sponges, S. spinulosa and occasional hydroids and bryozoans. The bryozoan Amathia lendigera can also become abundant amongst the seaweeds during the summer months.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Electra pilosa 15 Frequent 41-60%
Plocamium cartilagineum 14 Frequent 41-60%
Halurus flosculosus 11 Frequent 41-60%
Hypoglossum hypoglossoides 9 Occasional 41-60%
Foliose red algae 5 Abundant 41-60%
Corallinaceae 4 Occasional 21-40%
Amphipoda 4 Abundant 21-40%
Porifera indet crusts 4 Rare 21-40%
Cryptopleura ramosa 3 Common 21-40%
Heterosiphonia plumosa 3 Frequent 21-40%
Lanice conchilega 3 Occasional 21-40%
Phyllophora crispa 3 Occasional 21-40%
Calliblepharis ciliata 2 Common 21-40%
Caprellidae 2 Common 21-40%
Tubularia indivisa 2 Rare 21-40%
Dictyota dichotoma 1 Occasional 21-40%
Molgula manhattensis 1 Rare 21-40%
Mytilus edulis 1 21-40%

Similar biotopes or habitat types

This biotope occurs in deeper water below the kelp park with a higher diversity of sponges like H. panicea and D. fragilis.

This biotope occurs in deeper water below the kelp park with a high abundance of the brown seaweeds Dictyopteris polypodioides (Frequent) and D. dichotoma (Common). It also has a higher diversity of sponges like H. panicea and D. fragilis.

This biotope occurs on mixed, mobile substrata and is characterised by red seaweeds such as Halarachnion ligulatum, Lomentaria orcadensis, Naccaria wiggii and Compsothamnion thuioides that thrive in these conditions.

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