Skip to Content

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.

   Coralline crusts and crustaceans on mobile boulders or cobbles in surge gullies

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Very exposed, Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Boulders, cobbles, often with pebbles or gravel
Zone Infralittoral
Depth Band 0-5 m, 5-10 m, 10-20 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 IR.FIR.SG.CC.Mo Coralline crusts and crustaceans on mobile boulders or cobbles in surge gullies

  • 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.


Highly mobile and scoured boulders and cobbles found on cave and gully floors and which often appear bare. Where there is sufficient light and stability, however, the boulders are encrusted by coralline algal crusts. Barnacles Balanus crenatus and keelworms Spirobranchus triqueter may survive in areas protected from severe abrasion. Crabs such as Cancer pagurus and Carcinus maenas may occur, often beneath and between the rocks, along with the gastropod Calliostoma zizyphinum. The anemone Actinia equina may be present in low numbers.


The slightly less-scoured walls often found above this biotope in caves and gullies are generally characterised by a similar, but richer community of scour-tolerant Balanus crenatus, Spirobranchus triqueter, coralline crusts and spirorbid worms (CC.BalPom). This impoverished biotope may form an intermediate between barren gravel and slightly more stable larger pebbles and cobbles which are covered by algae that are often found in the mouths of caves (FoSwCC).

Temporal variation

Winter storms periodically mobilise the boulders and cobbles, causing abrasion to any seasonal biota that may have developed over the calmer summer months.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Corallinaceae 23 Common 21-40%
Carcinus maenas 23 Rare 21-40%
Rhodophyta indet.(non-calc.crusts) 18 Frequent 21-40%
Calliostoma zizyphinum 13 Occasional 21-40%
Urticina felina 12 Occasional 21-40%
Cancer pagurus 11 Occasional 21-40%

Similar biotopes or habitat types

Occurs in similar conditions as IR.FIR.SG.CC.Mo but has a higher species diversity and has a high abundance of the brown seaweed Desmarestia aculeata.

Severely scoured vertical infralittoral rock with B. crenatus and/or P. triqueter with spirorbid worms and coralline crusts. Often occurs on nearby vertical rock.

This biotope occurs in surge gully entrances on bedrock. The less scoured, more stable substrata allow foliose seaweeds develop.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) CC.Mob
1996 (6.95) EIR.Bcre

Back to top