Description of biotope or habitat type
Laminaria saccharina and Psammechinus miliaris on variable salinity grazed infralittoral rock
Habitat (physical) description
|Salinity||Reduced (18-30ppt), Low (<18ppt)|
|Wave exposure||Very sheltered, Extremely sheltered|
|Tidal streams||Weak (>1 kn), Very weak (negligible)|
|Substratum||Bedrock; boulders and cobbles|
|Depth Band||0-5 m, 5-10 m|
|Other Features||Heavily urchin-grazed|
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
Sheltered bedrock, boulders and cobbles, in areas of reduced salinity, with kelp Laminaria saccharina, and depauperate coralline-encrusted rock supporting few foliose seaweeds but many grazing urchins Psammechinus miliaris and Echinus esculentus. The coralline crusts are typically Lithothamnion glaciale, while the brown crusts can be Pseudolithoderma extensum. Encrusting polychaetes Pomatoceros triqueter, resistant to the grazing, are also present on most of the rock. The grazing fauna are a significant component of this biotope; large numbers of P. miliaris are typically present, although where absent the brittlestar Ophiothrix fragilis may occur. Other grazers prevalent on the rock include the chiton Tonicella marmorea, the limpet Tectura testudinalis and the gastropod Gibbula cineraria. A combination of grazing pressure and lowered salinity maintains a low diversity of species in this biotope, with foliose and filamentous seaweeds generally absent or reduced to small tufts by grazing. In stark contrast to the range of seaweeds present in the L. saccharina forests (Lsac.Ft) the only red seaweed consistently found in this biotope is Phycodrys rubens. The range of fauna is similarly low, with a conspicuous absence of hydroids and bryozoans. Bedrock and boulders provide a firm substrate on which ascidians Ciona intestinalis and Ascidia mentula and the bivalve Modiolus modiolus can attach. The crabs Pagurus bernhardus and Carcinus maenas can usually be found here, though Necora puber typically is absent due to the brackish conditions. The starfish Asterias rubens along with the whelk Buccinum undatum can be present. The substratum on which this biotope occurs varies from bedrock to boulders or cobbles on sediment. The kelp band is relatively narrow and shallow (upper 5 m) compared to Lsac.Ft, although the grazed coralline encrusted rock extends deeper. This depth limit becomes shallower towards the heads of the sealochs. Geographical distribution This biotope is restricted to the west coast of Scotland, usually near the head of fjordic sealochs, which are influenced by freshwater run-off.
Where circalittoral rock occurs below this biotope, it often supports a brachiopod/anthozoan community (NeoPro); where mixed substrata occurs below or adjacent, beds of Modiolus modiolus are common (ModHAs or ModHo).
If the grazing pressure is reduced (i.e. a decrease in the number of grazing echinoderms present) there may be an increase in filamentous and foliose seaweeds although the diversity will remain low compared to full saline sites.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
|Pagurus bernhardus||3||Occasional||41-60 %|
|Carcinus maenas||3||Occasional||41-60 %|
|Gibbula cineraria||2||Frequent||41-60 %|
|Tectura testudinalis||1||Occasional||21-40 %|
|Buccinum undatum||2||Occasional||41-60 %|
|Modiolus modiolus||2||Occasional||41-60 %|
|Asterias rubens||4||Occasional||61-80 %|
|Ophiothrix fragilis||2||Occasional||41-60 %|
|Psammechinus miliaris||18||Frequent||81-100 %|
|Echinus esculentus||2||Occasional||41-60 %|
|Ciona intestinalis||2||Occasional||41-60 %|
|Lithothamnion glaciale||4||Common||41-60 %|
|Phycodrys rubens||2||Occasional||41-60 %|
|Pseudolithoderma extensum||2||Abundant||21-40 %|
|Laminaria saccharina||18||Common||81-100 %|
Not applicable or unknown.