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Marine Habitat Classification

Description of biotope or habitat type

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   Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed, Sheltered, Very sheltered
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Maerl gravel; coarse sand
Zone Infralittoral - upper, Infralittoral
Depth Band 0-5 m, 5-10 m, 10-20 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 SS.SMp.Mrl.Pcal.R <I>Phymatolithon calcareum</I> maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand

  • 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.


Upper infralittoral maerl beds characterised by Phymatolithon calcareum in gravels and sand with a wide variety of associated red seaweeds. These algae typically include Dictyota dichotoma, Plocamium cartilagineum, Phycodrys rubens, Chondrus crispus, Halarachnion ligulatum, Chylocladia verticillata, Hypoglossum hypoglossoides and Nitophyllum punctum. These species are not restricted to maerl beds but their abundance on maerl beds differentiates this biotope from Pcal.Nmix. Anthozoans and echinoderms are much less common in this biotope than in Pcal.Nmix, which typically occurs deeper than Pcal.R.


No situation data available.

Temporal variation

No temporal data available.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Cerianthus lloydii 2 Frequent 41-60 %
Chaetopterus variopedatus 1 Occasional 41-60 %
Lanice conchilega 1 Occasional 21-40 %
Pomatoceros triqueter 2 Occasional 41-60 %
Pagurus bernhardus 5 Frequent 61-80 %
Liocarcinus depurator 2 Occasional 41-60 %
Gibbula cineraria 3 Occasional 41-60 %
Asterias rubens 6 Occasional 81-100 %
Echinus esculentus 1 Occasional 41-60 %
Bonnemaisonia asparagoides 1 Occasional 21-40 %
Phymatolithon calcareum 16 Abundant 81-100 %
Cystoclonium purpureum 1 Occasional 21-40 %
Plocamium cartilagineum 3 Frequent 61-80 %
Lomentaria clavellosa 1 Occasional 41-60 %
Nitophyllum punctatum 2 Occasional 41-60 %
Phycodrys rubens 2 Occasional 41-60 %
Brongniartella byssoides 2 Occasional 41-60 %
Trailliella intricata 1 Frequent 21-40 %
Dictyota dichotoma 4 Occasional 61-80 %
Desmarestia aculeata 2 Occasional 41-60 %
Desmarestia viridis 2 Occasional 41-60 %
Chorda filum 1 Frequent 21-40 %
Laminaria saccharina 6 Frequent 61-80 %
Ulva 2 Occasional 41-60 %

Similar biotopes or habitat types

Pcal.R is similar but shallower with more red seaweeds

Classification history of this biotope or habitat type

Classification version Code
97.06 IGS.Phy.R

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