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Marine Habitat Classification

Description of biotope or habitat type

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   Alaria esculenta on exposed sublittoral fringe bedrock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed
Tidal streams Very strong (>6 kn), Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock; very large boulders
Zone Sublittoral fringe
Depth Band 0-5 m, Lower shore
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 IR.HIR.KFaR.Ala <I>Alaria esculenta</I> on exposed sublittoral fringe bedrock

  • 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.


Exposed sublittoral fringe bedrock with an Alaria esculenta forest and an encrusting fauna of the mussel Mytilus edulis and barnacles such as Semibalanus balanoides. The kelp Laminaria digitata can be part of the canopy. Underneath the canopy are red seaweeds such as Mastocarpus stellatus and Palmaria palmata, while encrusting coralline red algae such as Lithothamnion graciale covers the rock surface. The limpet Patella vulgata can be found grazing the rock surface, while the whelk Nucella lapillus is preying on the limpets, barnacles and mussels. Two variants of this biotope are described. In more wave exposed conditions Laminaria digitata is absent and the rock surface is often characterised by dense patches of mussels (Ala.Myt). In slightly less exposed sites the A. esculenta is mixed with L. digitata (Ala.Ldig).


This biotope is found in the sublittoral fringe on exposed shores, typically occupying the extreme lower shore down to 1 or 2 m depth, although it can also extend down to 15 m depth on very exposed coasts. It is generally found below the mussel-barnacle zone of the lower shore (MytB) or a narrow band of the seaweed-dominated biotopes featuring dense Himanthalia elongata or red seaweeds (Him, Mas). Below the A. esculenta zone, the upper infralittoral rock generally supports a Laminaria hyperborea kelp community (LhypFa, LhypR.Ft or Lhyp.Ft).

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Alaria esculenta 32 Abundant 81-100%
Mytilus edulis 14 Common 61-80%
Corallina officinalis 11 Frequent 61-80%
Patella vulgata 8 Common 41-60%
Corallinaceae 6 Abundant 41-60%
Lithothamnion glaciale 6 Abundant 21-40%
Laminaria digitata 5 Common 41-60%
Semibalanus balanoides 4 Frequent 41-60%
Mastocarpus stellatus 2 Frequent 41-60%
Palmaria palmata 1 Occasional 21-40%
Nucella lapillus 1 Occasional 21-40%

Similar biotopes or habitat types

Occur on very exposed bedrock shores. Dense anthozoans including Corynactis viridis and Phellia gausapata and sponges such as Haliclona urceolus and Myxilla fimbriata can be present.


IR.HIR.KFAR.Ala Alaria esculenta on exposed sublittoral fringe bedrock, SW side, Rockall. Keith Hiscock© JNCC
IR.HIR.KFAR.Ala Alaria esculenta on exposed sublittoral fringe bedrock, SW side, Rockall. Keith Hiscock© JNCC

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