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Marine Habitat Classification

Description of biotope or habitat type

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   Alaria esculenta and Laminaria digitata on exposed sublittoral fringe bedrock

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)
Substratum Bedrock
Zone Sublittoral fringe
Depth Band 0-5 m, Lower shore
Other Features On vertical and very steep rock

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.Ldig <I>Alaria esculenta</I> and <I>Laminaria digitata</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 characterised by a mixture of the kelps Laminaria digitata and Alaria esculenta with an understorey of red seaweeds including Palmaria palmata and Corallina officinalis with encrusting coralline algal on the rock surface. Anthozoans such as Halichondria panicea, the mussel Mytilus edulis and the barnacle Semibalanus balanoides can be found attached in cracks and crevices. The limpets Patella vulgata or on southern shores Patella ulyssiponensis can be found in their characteristic "scars" grazing the biofilm/algal crusts on the rock surface, while the limpet Patella pellucida is restricted to grazing the kelp fronds. Colonies of the bryozoan Electra pilosa can cover the red seaweeds Mastocarpus stellatus and Chondrus crispus or the rock surface.


Ala.Ldig represents an intermediate on the wave exposure gradient, with pure stands of A. esculenta (Ala.Myt) being found on more exposed shores and pure L. digitata (Ldig) on more sheltered shores. This biotope usually occurs immediately above a sublittoral Laminaria hyperborea forest (LhypR or Lhyp), although a narrow band of L. digitata (Ldig) may occur between these two zones, particularly on less exposed shores. In southwest England a zone of mixed kelp forest L. hyperborea and Laminaria ochroleuca may occur below the A. esculenta (Lhyp.Loch). A number of different biotopes can occur above Ala.Ldig; most commonly these are the mussel-barnacle zone (MytB), Himanthalia elongata (Him), a red algal turf or a Fucus serratus-red algal mosaic (Fser.R) on the less exposed shores. This biotope also occurs on steep and vertical shores of moderately exposed coasts where a localised increase in wave action restricts the growth of L. digitata. As a result of this increased wave action the L. digitata plants are usually small and often show signs of damage.

Temporal variation

There may be seasonal changes in the amount of ephemeral seaweeds due to disturbance caused by winter storms.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Laminaria digitata 22 Abundant 81-100%
Alaria esculenta 20 Common 81-100%
Corallinaceae 10 Abundant 61-80%
Corallina officinalis 8 Common 61-80%
Mastocarpus stellatus 4 Frequent 41-60%
Mytilus edulis 4 Frequent 41-60%
Palmaria palmata 3 Frequent 41-60%
Semibalanus balanoides 2 Occasional 21-40%
Chondrus crispus 2 Occasional 41-60%
Halichondria panicea 2 Occasional 41-60%
Patella pellucida 2 Frequent 41-60%
Patella vulgata 2 Frequent 41-60%
Oshurkovia littoralis 2 Frequent 21-40%
Electra pilosa 1 Frequent 41-60%
Patella ulyssiponensis 1 Frequent 21-40%

Similar biotopes or habitat types

Occurs on more exposed shores. A. esculenta and M. edulis is abundant and Lithothamnion spp. is the dominant coralline crust. L. digitata is absent and the diversity of red seaweeds are lower.

Occurs on less exposed shores. L. digitata is the dominant kelp (Abundant), while the abundance of A. esculenta is low (Occasional).

Classification history of this biotope or habitat type

Classification version Code

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