Biodiversity & Conservation

Beds of dead maerl

Dead maerl beds

Beds of dead maerl
Distribution map

Dead maerl beds 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 Maerl beds (live and dead) have a patchy distribution around the coast of the British Isles. They are widespread around the west coast of Scotland, in the Western Isles, Orkney and Shetland but restricted to Milford Haven, the Pembrokeshire Islands and the Llyn Peninsula in Wales. Beds are rare in England, reported from Dorset, the Isles of Scilly and Lundy but with extensive beds in the Fal Estuary and mouth of the Helford River. Extensive beds occur on the north east coast of Northern Ireland, and along the west coasts of Ireland (e.g. Galway Bay). In Europe, maerl beds are found in the Mediterranean, and on the Atlantic coast from Norway and Denmark south to Portugal, Morocco and Mauritania on the African coast (Birkett et al. 1998). Few of the distributional records distinguish between ‘live’ and ‘dead’ beds. The map (above) only shows confirmed records of dead beds off the Isle of Bute and in Falmouth Bay.
National importance Not available

Text page icon Description of biotope

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

Maerls are calcareous red algae that grow as nodules (occasionally crusts) forming dense but relatively open beds of algal gravel. Beds of maerl form in coarse clean sediments of gravels and clean sands, and occur either on the open coast or in tide-swept channels of marine inlets (the latter often stony). In fully marine conditions, the dominant maerl is typically Phymatolithon calcareum or Lithothamnion corallioides in England. Dead maerl beds may be composed of smaller maerl fragments than live beds resulting in a denser, less heterogeneous structure, and lack the diversity of mobile epifauna and maerl specific epiflora characteristic of live maerl beds. However, they support diverse communities of burrowing infauna, especially bivalves, and interstitial invertebrates; including suspension feeds polychaetes and echinoderms. Thicker maerl beds occur in areas of water movement (wave or current based) while sheltered beds tend to be thinner with more epiphytes. The associated community varies with underlying and surrounding sediment type, water movement, depth of bed and salinity.

Additional information icon Additional information

This review can be cited as follows:

Tyler-Walters, H. 2013. Beds of dead maerl. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/11/2015]. Available from: <>