Natural England - Common maerl

Common maerl

Phymatolithon calcareum

Common mearl © Lin Baldock

Common maerl © 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.

Brief description of European distribution

Distribution map

Distribution map: (320kb)pdf document

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

UKBAP Priority Species

Species of principal importance for the purpose of conserving of biodiversity under the Natural Environment and Rural Communities Act 2006

Maerl beds are a UKBAP Priority Habitat, and are on the OSPAR List of Threatened and/or Declining Species and Habitats.

Further information sources

Maerl - Phymatolithon calcareumexternal link (MarLIN)

Maerl bedsexternal link (UKBAP)

Interesting fact

Deep deposits of dead maerl plants (called sub-fossils) have been found in Cornwall.  They show that maerl once covered a much wider area than today.