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.

   Ascophyllum nodosum on full salinity mid eulittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams
Substratum Bedrock; boulders; cobbles
Zone Eulittoral - mid
Depth Band
Other Features Disturbance allows Fucus vesiculosus to occupy patches in the canopy

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.F.Asc.FS <I>Ascophyllum nodosum</I> on full 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.


Bedrock, stable boulders and cobbles in the mid-eulittoral zone of moderately exposed to extremely sheltered shores, in fully marine conditions, characterised by a dense canopy of the wrack Ascophyllum nodosum. Another wrack Fucus vesiculosus may in some places co-dominate the canopy. The hydroid Dynamena pumila can form colonies on the wracks F. vesiculosus and Fucus serratus. Variations in the ratio of A. nodosum and F. vesiculosus in the overlying canopy have little effect on the under-storey species. Beneath the canopy are a diverse array of filamentous and foliose red seaweeds, including Mastocarpus stellatus, Chondrus crispus, Gelidium pusillum and coralline crusts. The filamentous red seaweed Vertebrata lanosa is usually present on A. nodosum as an epiphyte. A few green seaweeds including Cladophora rupestris and Ulva spp. are also present in moderate to low densities. On the bedrock and boulders beneath the seaweed canopy is a fauna including the barnacle Semibalanus balanoides, the limpet Patella vulgata, tube-forming spirorbid polychaetes and the anemone Actinia equina. The latter can be present in damp cracks and crevices. On and among the seaweeds are mobile species including the winkles Littorina littorea and Littorina obtusata, the whelk Nucella lapillus or even the crab Carcinus maenas. At the top of the A. nodosum zone there might be the occasional presence of the olive green lichen Verrucaria mucosa.


This biotope is usually found between the wrack Fucus spiralis (Fspi) and F. serratus dominated biotopes (Fserr), 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 is replaced by F. vesiculosus (FvesB; Fves). Asc.FS can occur on more exposed shores, where there is localised shelter.

Temporal variation

A. nodosum can reach an age of 25 years on sheltered shores and the communities are, once established, usually very 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 28 Abundant 81-100%
Fucus vesiculosus 8 Frequent 61-80%
Semibalanus balanoides 7 Frequent 61-80%
Patella vulgata 6 Frequent 61-80%
Vertebrata lanosa 6 Frequent 61-80%
Corallinaceae 4 Frequent 41-60%
Littorina littorea 4 Occasional 61-80%
Littorina obtusata 4 Frequent 41-60%
Actinia equina 2 Occasional 41-60%
Carcinus maenas 2 Occasional 41-60%
Dynamena pumila 2 Occasional 41-60%
Fucus serratus 2 Occasional 41-60%
Spirorbinae 2 Frequent 21-40%
Nucella lapillus 2 Occasional 41-60%
Verrucaria mucosa 1 Occasional 21-40%
Chondrus crispus 1 Occasional 21-40%
Cladophora rupestris 1 Frequent 21-40%
Ulva intestinalis 1 Occasional 21-40%
Gelidium pusillum 1 Frequent 21-40%
Mastocarpus stellatus 1 Occasional 41-60%

Similar biotopes or habitat types

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 bedrock or mixed substrata with variable salinity. Coralline crusts and C. crispus, N. lapillus and A. equina are usually absent in this species impoverished biotope.

Occurs on mixed substrata. Has a lower abundance and diversity of red seaweeds and lacks species such as D. pumila and V. mucosa.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) SLR.Asc.Asc

Back to top