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Marine Habitat Classification

Description of biotope or habitat type

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   Pomatoceros triqueter with barnacles and bryozoan crusts on unstable circalittoral cobbles and pebbles

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Very exposed, Exposed, Moderately exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum Cobbles and pebbles with sand
Zone Circalittoral
Depth Band 5-10 m, 10-20 m, 20-30 m, 30-50 m
Other Features Mobile substrata

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.SCS.CCS.PomB <I>Pomatoceros triqueter</I> with barnacles and bryozoan crusts on unstable circalittoral cobbles and pebbles

  • 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.


This biotope is characterised by a few ubiquitous robust and/or fast growing ephemeral species which are able to colonise pebbles and unstable cobbles and slates which are regularly moved by wave and tidal action. The main cover organisms tend to be restricted to calcareous tube worms such as Pomatoceros triqueter (or P. lamarcki), small barnacles including Balanus crenatus and Balanus balanus, and a few bryozoan and coralline algal crusts. Scour action from the mobile substratum prevents colonisation by more delicate species. Occasionally in tide-swept conditions tufts of hydroids such as Sertularia argentea and Hydrallmania falcata are present. This biotope often grades into SMX.FluHyd which is characterised by large amounts of the above hydroids on stones also covered in Pomatoceros and barnacles. The main difference here is that SMX.FluHyd, seems to develop on more stable, consolidated cobbles and pebbles or larger stones set in sediment in moderate tides. These stones may be disturbed in the winter and therefore long-lived and fragile species are not found.


This biotope is found on exposed open coasts as well as at the entrance to marine inlets.

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
Lanice conchilega 1 Occasional 21-40 %
Pomatoceros 4 Common 1-20 %
Pomatoceros triqueter 61 Frequent 61-80 %
Balanus balanus 2 Occasional 21-40 %
Balanus crenatus 3 Frequent 21-40 %
Bryozoa indet crusts 5 Frequent 21-40 %
Asterias rubens 6 Occasional 41-60 %
Echinus esculentus 7 Occasional 41-60 %

Similar biotopes or habitat types

A similar shallow water biotope occurring on cobbles at the base of surge gullies

As substratum stability increases (larger rocks and less turbulent wave action) more species are able to colonise the sea bed. FluHyd, FluCoAs.SmAs and ByErSp.DysAct in that order, represent the progression from PomB to more stable mixed substrata although still with a high proportion of scour- and sand-tolerant species.

Classification history of this biotope or habitat type

Classification version Code
97.06 ECR.PomByC

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