Biodiversity & Conservation

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



Image Christine Howson - Lithothamnion glaciale nodules amongst pebbles with the sunstar Crossaster papposus, Isle of Lewis. Image width ca 20 cm.
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Distribution map

SS.IGS.Mrl.Lgla recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats
  • UK_BAP

Text page icon Habitat description

Map icon Distribution of biotope in Britain and Ireland The distribution of Lithothamnion glaciale extends to the southern British Isles and is most abundant off the western coast of Scotland, Orkney and the Shetland Isles. This biotope has been recorded in only a few locations on the west coast of Scotland and in the Shetland Isles.
National importance Scarce

Text page icon Description of biotope

For a full description of this biotope including characterizing species, distribution, survey information and references visit JNCC

Upper infralittoral tide-swept channels of coarse sediment subject to variable or reduced salinity which support distinctive beds of Lithothamnion glaciale maerl 'rhodoliths'. Phymatolithon calcareum may also be present as a more minor maerl component. This biotope can often be found at the upper end of Scottish sea lochs where the variable salinity of the habitat may not be immediately obvious. Associated fauna and flora may include species found in other types of maerl beds (and elsewhere), e.g. Chaetopterus variopedatus, Lanice conchilega, Mya truncata, Plocamium cartilagineum and Phycodrys rubens. IGS.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 and Henricia oculata are also fairly typically present at sites. In Scottish lagoons (obs) this biotope may show considerable variation but the community falls within the broad description defined here. (Information taken from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Additional information icon Additional information

This review can be cited as follows:

Jackson, A. 2006. Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/11/2015]. Available from: <>