Description of biotope or habitat type
Fucus serratus and large Mytilus edulis on variable salinity lower eulittoral rock
Habitat (physical) description
|Salinity||Variable (18-35 ppt)|
|Wave exposure||Sheltered, Very sheltered, Extremely sheltered|
|Tidal streams||Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)|
|Substratum||Bedrock; boulders; cobbles|
|Zone||Eulittoral - lower|
|Depth Band||Lower shore|
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'
Point data based on records in the UK Marine Recorder Snapshot.
Areas of very sheltered lower eulittoral rock or mixed substrata subject to variable salinity, which support an impoverished community dominated by the wrack Fucus serratus. The hydroid Dynamena pumila can form colonies on the F. serratus and clumps of large individuals of the mussel Mytilus edulis may be present on the bedrock beneath. The canopy of F. serratus is not usually as dense as in the other F. serratus dominated biotopes due the presence of the wracks Ascophyllum nodosum and Fucus vesiculosus, which are better adapted to the variable salinity. A few red seaweeds are present which includes the species Mastocarpus stellatus, Chondrus crispus and coralline crusts. Underneath the canopy is a sparse fauna consisting of barnacles Semibalanus balanoides, Balanus crenatus and Elminius modestus, the limpet Patella vulgata or the occasional presence of the winkles Littorina obtusata and Littorina mariae and the crab Carcinus maenas. The tube-forming polychaetes Pomatoceros triqueter or spirorbid polychaetes can be found. In areas (such as the Scottish sea lochs) where variable salinity water passes through tide-swept narrows and the associated biota is impoverished such records should be classified as FserVS rather than FserT.
This biotope may be found below the variable salinity F. vesiculosus dominated biotope or A. nodosum dominated biotope (AscVS; FvesVS), particularly in Scottish sea lochs. FserVS can be found above the biotopes dominated by the kelp Laminaria saccharina (LsacVS.Psa; LsacVS.Phy).
The canopy of F. serratus is not as dense as in the other F. serratus dominated biotopes due the presence of the wracks A. nodosum and F. vesiculosus, which are better adapted to the variable salinity. They will therefore out-compete F. serratus on the lower shore and an ecological shift can occur (In the Baltic Sea F. vesiculosus is the dominant sublittoral brown seaweed). Due to the variable or low salinity conditions the individual red seaweeds may not be as large as specimens found in fully marine conditions and they can lack sexually reproductive structures.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
|Dynamena pumila||1||Occasional||21-40 %|
|Pomatoceros triqueter||3||Occasional||21-40 %|
|Elminius modestus||2||Common||21-40 %|
|Semibalanus balanoides||10||Frequent||61-80 %|
|Balanus crenatus||2||Occasional||21-40 %|
|Carcinus maenas||2||Occasional||41-60 %|
|Littorina obtusata/mariae||2||Frequent||21-40 %|
|Patella vulgata||2||Occasional||21-40 %|
|Littorina littorea||6||Frequent||41-60 %|
|Mytilus edulis||6||Frequent||41-60 %|
|Chondrus crispus||2||Occasional||41-60 %|
|Mastocarpus stellatus||2||Frequent||21-40 %|
|Ascophyllum nodosum||3||Occasional||41-60 %|
|Fucus serratus||37||Common||81-100 %|
|Fucus vesiculosus||5||Occasional||41-60 %|
|Enteromorpha intestinalis||1||Occasional||21-40 %|