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Marine Habitat Classification

Description of biotope or habitat type

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   Ascophyllum nodosum and Fucus vesiculosus on variable salinity mid eulittoral rock

Physical habitat description

Salinity Variable (18-35 ppt)
Wave exposure Very sheltered, Extremely sheltered
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Bedrock; boulders; cobbles
Zone Eulittoral
Depth Band
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 LR.LLR.FVS.AscVS <I>Ascophyllum nodosum</I> and <I>Fucus vesiculosus</I> on variable salinity mid eulittoral rock

  • 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'

Point data based on records in the UK Marine Recorder Snapshot.


Very sheltered to extremely sheltered mid eulittoral bedrock, boulders or cobbles subject to variable salinity characterised by an impoverished community dominated by a mixture of the wracks Ascophyllum nodosum and Fucus vesiculosus. Underneath the canopy are a few green seaweeds including Ulva intestinalis and Cladophora spp., while the red seaweed Vertebrata lanosa can be found as an epiphyte on A. nodosum. On the rock and among the boulders are the winkles Littorina littorea and Littorina saxatilis, the crab Carcinus maenas, the barnacles Semibalanus balanoides and Austrominius modestus and even the occasional mussel Mytilus edulis. Among the seaweeds and underneath the boulders a variety of gammarids can be found.


This biotope usually lies below the Fucus spiralis biotope (Fspi.VS) or the Fucus ceranoides dominated biotopes (Fcer) and above the variable salinity F. serratus dominated biotope (Fserr.VS), although on some shores a narrow zone of F. vesiculosus (Fves) may occur immediately above the A. nodosum. With increasing wave exposure the A. nodosum canopy can be more dense (Asc.FS).

Temporal variation

A. nodosum can reach an age of 25 years and the communities are usually stable. F. vesiculosus or F. serratus can occur in patches where the A. nodosum has been removed.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Ascophyllum nodosum 35 Abundant 81-100%
Fucus vesiculosus 10 Frequent 61-80%
Semibalanus balanoides 8 Frequent 41-60%
Carcinus maenas 6 Occasional 61-80%
Littorina littorea 6 Occasional 41-60%
Austrominius modestus 5 Frequent 41-60%
Mytilus edulis 5 Occasional 41-60%
Vertebrata lanosa 5 Frequent 41-60%
Ulva intestinalis 3 Occasional 41-60%
Gammaridae 1 Frequent 21-40%
Cladophora 1 Rare 21-40%
Littorina saxatilis 1 Occasional 21-40%

Similar biotopes or habitat types

Occurs on bedrock in full salinity. This biotope has higher species diversity and species such as the red coralline crusts and the foliose red seaweed Chondrus crispus, the whelk Nucella lapillus and anemone Actinia equina are usually present.

Occurs on bedrock or mixed substrata with strong tidal streams. High diversity of filter-feeders including the sponges Leucosolenia spp. and Grantia compressa, the hydroid Clava multicornis and the sea squirt Dendrodoa grossularia.

Occurs on mixed substrata in full marine conditions. Similar species composition, but lacks species, such as D. pumila and E. modestus.

Classification history of this biotope or habitat type

Classification version Code

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