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Marine Habitat Classification

Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   Polyides rotunda, Ahnfeltia plicata and Chondrus crispus on sand-covered infralittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock, cobbles and pebbles with mobile sand
Zone Infralittoral
Depth Band 5-10 m
Other Features Sand-covered rock

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.HIR.KSed.ProtAhn <I>Polyides rotunda</I>, <I>Ahnfeltia plicata</I> and <I>Chondrus crispus</I> on sand-covered 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.


Low-lying rock surrounded by mobile sand and often subject to burying by the sand, with a turf of resilient red seaweeds Chondrus crispus, Polyides rotunda and Ahnfeltia plicata typically protruding through the sand on the upper surfaces of the rock. Other scour-tolerant seaweeds include Rhodomela confervoides, Phyllophora pseudoceranoïdes, Phyllophora crispa, Furcellaria lumbricalis, Gracilaria gracilis, Ceramium rubrum, Plocamium cartilagineum, Heterosiphonia plumosa, Cryptopleura ramosa and Dilsea carnosa. Coralline crusts typically cover the rock, while scattered individuals of the brown seaweeds Halidrys siliquosa, Cladostephus spongiosus, Dictyota dichotoma and Saccharina latissima can be present. The large anthozoan Urticina felina can occur in this biotope but there are few other conspicuous animals.


This biotope occurs on shallow sand-covered rock, often below bedrock and boulders supporting kelp forest, which is above the effect of, sand scour (Lhyp) or abutting sand-scoured kelp on bedrock (XKScrR). It may also be found adjacent to the shallow kelp and Chorda filum biotope (LsacChoR) and similarly can be surrounded by a variety of sediment biotopes.

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Chondrus crispus 15 Frequent 81-100%
Polyides rotunda 10 Frequent 61-80%
Corallinaceae 9 Frequent 61-80%
Ahnfeltia plicata 6 Frequent 41-60%
Dilsea carnosa 6 Occasional 41-60%
Furcellaria lumbricalis 4 Occasional 41-60%
Saccharina latissima 4 Occasional 41-60%
Cryptopleura ramosa 3 Occasional 41-60%
Heterosiphonia plumosa 3 Frequent 41-60%
Phyllophora crispa 3 Occasional 41-60%
Phyllophora pseudoceranoides 3 Frequent 41-60%
Rhodomela confervoides 3 Frequent 41-60%
Dictyota dichotoma 2 Occasional 21-40%
Plocamium cartilagineum 2 Occasional 41-60%
Ceramium nodulosum 1 Frequent 21-40%
Cladostephus spongiosus 1 Occasional 21-40%
Gracilaria gracilis 1 Frequent 21-40%
Halidrys siliquosa 1 Occasional 21-40%
Urticina felina 1 Occasional 21-40%
Ulva 1 Occasional 21-40%

Similar biotopes or habitat types

Lack of large boulders or prominent bedrock in IR.HIR.KSed.ProtAhn prevents dominance by H. siliquosa or kelps.

Classification history of this biotope or habitat type

Classification version Code
2015 (15.03) IR.HIR.KSed.ProtAhn
1997 (97.06) MIR.PolAhn

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