Latin name: Phymatolithon calcareum,
Global Distribution: Norway to northern Spain, including western Baltic and Mediterranean
UK Distribution: Abundant around the west coasts of Scotland and Ireland. Also recorded along the east coast of scotland, around Orkney and the Shetland Isles and the south coast of England
Size: 7cm in diameter
Diet: Photosynthesis
Habitat: In sand, mud, or gravel sheltered from wave action, but with substantial water flow. Depths of 1-30m

Maerl is a collective term for certain red coralline algae that grow unattached on the seabed. Phymatolithon calcareum is a fragile, branched species of maerl, that usually resembles a stag’s horns with a smooth surface with white flaky areas. Typically, they are found in association, and sometimes confused, with two other maerl species, Lithothamnion corallioides (in the southern British Isles) and Lithothamnion glaciale (in the northern British Isles).  

Maerl grows at a very slow rate, around 1mm per year, but given time they can create complex habitats that can rival those of seagrass beds and coral reefs. These habitats can support a variety of algae and invertebrates and even act as nursery habitats for commercial species such as cod, scallops and pollock. Unfortunately, because of their slow growth, it takes a long time for these diverse habitats to recover after they are hit by trawls and dredges.

Fun facts

  • Unfortunately, maerl has been dredged up for centuries to be used as fertiliser, and is still extracted today.
  • The white beaches of Western Scotland are actually made of washed up maerl that have been crushed by the waves and bleached in sunlight.