Common maerl

Phymatolithon calcareum


Common maerl (Phymatolithon calcareum) © Lin Baldock

It might be rock hard, and look like tiny knobbly stag’s antlers, but common maerl is actually a red seaweed with a hard, chalky skeleton.

Unlike many other seaweeds, common maerl does not need a hard surface to attach to, and so it can be found across a variety of seascapes, from mud to sand and pebbles. However, in common with all seaweeds, it needs sunlight to grow, and so is usually only found in shallow water (above 10m depth) or down as deep as light allows. Normally mauvish brown in colour, its surface can be either smooth or flaky.

The live plants usually grow lying on top of layers of dead maerl to form maerl beds.  These beds are very important for other marine creatures, which hide in amongst the maerl, or use it as a hard surface on which to settle and grow.

Maerl is at risk from scallop dredging and other mobile fishing gears, as well as from pollution.


European distribution

Common maerl is recorded from the south and west coasts of England, but is more abundant around the coasts of Scotland and Ireland.  It is the most widespread maerl species in Europe and is found from Norway and Denmark in the north to Portugal in the south, and into the Mediterranean Sea and in the Aegean.


Conservation status/need

  • Common Maerl FactThis is a UK BAP Priority Species (BAP species are now Species of Principal Importance/Priority Species).
  • Species of principal importance for the purpose of conservation of biodiversity under the Natural Environment and Rural Communities Act 2006
  • Listed on Annex V of the Habitats Directive
  • Maerl beds are a UK BAP Priority Habitat and are listed in Annex I of the Habitats Directive as a sub-feature of sandbanks and on the OSPAR List of Threatened and/or Declining Species and Habitats


Further information

Marine Life Information Network

JNCC - UK BAP Priority Species and Habitats