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Marine Habitat Classification

Description of biotope or habitat type

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   Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel

Physical habitat description

Salinity Full (30-35 ppt), 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)
Substratum Maerl; shell gravel; stones and coarse sediment
Zone Infralittoral
Depth Band 0-5 m, 5-10 m
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 SS.SMp.Mrl.Lgla <I>Lithothamnion glaciale</I> maerl beds in tide-swept variable salinity infralittoral gravel

  • 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.


Upper infralittoral tide-swept channels of coarse sediment in full or variable salinity conditions support distinctive beds of Lithothamnion glaciale maerl 'rhodoliths'. Phymatolithon calcareum may also be present as a more minor maerl component. Associated fauna and flora may include species found in other types of maerl beds (and elsewhere), e.g. Pomatoceros triqueter, Cerianthus lloydii, Sabella pavonina, Chaetopterus variopedatus, Lanice conchilega, Mya truncata, Plocamium cartilagineum and Phycodrys rubens. Lgla, however, also has a fauna that reflects the slightly reduced salinity conditions, e.g. Psammechinus miliaris is often present in high numbers along with other grazers such as chitons and Tectura spp. Hyas araneus, Ophiothrix fragilis, Ophiocomina nigra and the brown seaweed Dictyota dichotoma are also typically present at sites. In Scottish lagoons this biotope may show considerable variation but the community falls within the broad description defined here.


This biotope can often be found at the upper end of Scottish sealochs where the variable salinity of the habitat may not be immediately obvious.

Temporal variation

No temporal data available.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Cerianthus lloydii 1 Frequent 21-40 %
Pomatoceros triqueter 2 Frequent 21-40 %
Pagurus bernhardus 2 Frequent 21-40 %
Carcinus maenas 3 Occasional 41-60 %
Gibbula cineraria 1 Occasional 21-40 %
Buccinum undatum 1 Occasional 21-40 %
Ostrea edulis 1 Frequent 1-20 %
Asterias rubens 11 Occasional 81-100 %
Ophiothrix fragilis 12 Frequent 61-80 %
Ophiocomina nigra 12 Abundant 61-80 %
Psammechinus miliaris 3 Frequent 21-40 %
Echinus esculentus 1 Occasional 41-60 %
Corallina officinalis 3 Occasional 41-60 %
Lithothamnion glaciale 16 Abundant 61-80 %
Phymatolithon calcareum 2 Abundant 1-20 %
Chondrus crispus 2 Occasional 41-60 %
Trailliella intricata 1 Frequent 21-40 %
Dictyota dichotoma 6 Frequent 41-60 %
Chorda filum 1 Frequent 21-40 %
Laminaria saccharina 1 Occasional 21-40 %

Similar biotopes or habitat types

Not applicable or unknown.

Classification history of this biotope or habitat type

Classification version Code
97.06 IGS.Lgla

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