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.
- 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.
Description
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).
Situation
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
Unknown
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
