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.

   Foliose seaweeds and coralline crusts in surge gully entrances

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Bedrock; boulders
Zone Infralittoral
Depth Band 0-5 m, 5-10 m, 10-20 m
Other Features Boulder-scoured and wave-surged

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.FoSwCC Foliose seaweeds and coralline crusts in surge gully entrances

  • 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 found on steep wave-surged entrances to gullies and caves and on unstable boulders in the entrance to caves and gullies. The rock may be abraded by the movement of the boulders and cobbles in heavy surge and tends to be dominated by dense foliose seaweeds that grow rapidly in the calmer summer months. Beneath the foliose seaweeds the rock surface is typically covered with coralline crusts, which are longer-lived, and tolerant of abrasion. The flora of this biotope is relatively varied, depending upon the amount of light and degree of abrasion or rock mobility with red seaweeds such as Cryptopleura ramosa, Plocamium cartilagineum, Odonthalia dentata, Metacallophyllis laciniata, Phycodrys rubens, Hypoglossum hypoglossoides, Phyllophora crispa and Corallina officinalis. The brown seaweed Dictyota dichotoma also occurs in these conditions, since it is tolerant of some sand scour. During the summer months small fast-growing kelp plants can arise in this biotope, although the mobility of the substratum prevents the kelp from forming a kelp forest. Dense swathes of very young kelp such as Laminaria hyperborea are, however, not uncommon. The faunal community consist of the anemone Urticina felina, the sponge Halichondria panicea and the ascidian Dendrodoa grossularia. More mobile fauna include the echinoderms Asterias rubens and Echinus esculentus, the top shell Steromphala cineraria and the crab Cancer pagurus.


Further into the cave or gully, beyond the dense red seaweeds of FoSwCC, the vertical rock grades to either an ascidian and sponge dominated community or sponge crusts and anthozoans (CrSpAsAn/CrSpAsDenB). Further into the cave or gully the floor and any boulders or cobbles are generally scoured clean or may support coralline encrusting algae (CC.Mo). Above the red seaweeds, steep rock surfaces often support a kelp community (LhypR or Lhyp) or in shallower water Alaria esculenta is usually present (Ala.Myt).

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Corallinaceae 21 Abundant 81-100%
Cryptopleura ramosa 10 Frequent 61-80%
Plocamium cartilagineum 8 Frequent 41-60%
Odonthalia dentata 5 Occasional 41-60%
Urticina felina 5 Occasional 41-60%
Dictyota dichotoma 4 Occasional 21-40%
Asterias rubens 3 Occasional 41-60%
Metacallophyllis laciniata 3 Occasional 41-60%
Dendrodoa grossularia 3 Frequent 21-40%
Steromphala cineraria 3 Frequent 41-60%
Hypoglossum hypoglossoides 3 Occasional 41-60%
Phycodrys rubens 3 Occasional 21-40%
Halichondria panicea 2 Occasional 21-40%
Cancer pagurus 1 Occasional 21-40%
Corallina officinalis 1 Occasional 21-40%
Laminaria hyperborea 1 Occasional 21-40%
Phyllophora crispa 1 Occasional 21-40%
Echinus esculentus 1 Occasional 21-40%

Similar biotopes or habitat types

This biotope occurs in a similar depth and conditions as IR.FIR.SG.FoSwCC, though IR.HIR.KSed.Sac often occurs further away from the cave / gully entrance on larger boulders. As such, the greater (relative) stability of the boulders allows the opportunistic kelps to survive long enough to form a forest.


IR.FIR.SG.FoSwCC Foliose seaweeds and coralline crusts in surge gully entrances, SW side, Rockall. Christine Howson© JNCC
IR.FIR.SG.FoSwCC Foliose seaweeds and coralline crusts in surge gully entrances, SW side, Rockall. Christine Howson© JNCC

Back to top