Description of biotope or habitat type
Coralline crusts and crustaceans on mobile boulders or cobbles in surge gullies
Habitat (physical) 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|
|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.
- 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
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 Pomatoceros 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, Pomatoceros 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).
Winter storms periodically mobilise the boulders and cobbles, causing abrasion to any seasonal biota that may have developed over the calmer summer months.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
|Urticina felina||12||Occasional||21-40 %|
|Cancer pagurus||11||Occasional||21-40 %|
|Carcinus maenas||23||Rare||21-40 %|
|Calliostoma zizyphinum||13||Occasional||21-40 %|
|Rhodophycota indet.(non-calc.crusts)||18||Frequent||21-40 %|