Maerl beds



GB distribution

Compiled by: Leigh Jones, Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough PE1 IJY, UK.

Derived, in part, from: the UK marine biotope classification (Connor et al. 1997b) and a review undertaken for the UK Marine SACs Project (Birkett et al. 1998).


Classification Code Biotope(s)
Europe (EUNIS Nov. 1999) A4.1/B-IGS.Mrl.Phy Phymatolithon calcareum maerl beds in shallow-water clean gravel and coarse sand
  A4.4/B-IMX.MrlMx Maerl beds on shallow-water muddy mixed sediments
Wadden Sea - Not present/listed
Britain/Ireland (MNCR BioMar 97.06) IGS.Mrl


Maerl beds (open coasts/clean sediments)

Maerl beds (muddy mixed sediments)

France (ZNIEFF-MER) III.7.1 Fonds Lithothamnion (= Phymatolithon) calcareum, Lithothamnion corallioides


IGS.Mrl. Beds of maerl in coarse clean sediments of gravels and clean sands, which occur either on the open coast or in tide-swept channels of marine inlets (latter often stony). In fully marine conditions the dominant maerl is typically Phymatolithon calcareum (IGS.Phy), whilst under variable salinity conditions in some Scottish sealochs beds of Lithothamnion glaciale (IGS.Lgla) may develop.

IMX.MrlMx. Maerl beds of the genus Lithothamnion or Lithophyllum which develop on shallow sublittoral muddy gravels. Such sediments are found in marine inlets, such as rias and sealochs, usually in fully marine or near marine conditions where significant tidal currents are lacking. Three species of maerl may dominate; L. corallioides (IMX.Lcor), which is relatively widespread, and Lithophyllum dentatum and L. fasciculatum (IMX.Lden and IMX.Lfas) which have restricted distributions in Ireland.

GB distribution

(from MNCR database March 1999)











Habitat requirements

Species composition and biodiversity

Ecological relationships

Sensitivity to human activities

Conservation and protection status