Maerl beds

Maerl beds provide vital shelter to many and varied marine creatures. Their protection is crucial to managing our seas wisely.

Living maerl is a purple-pink hard seaweed that forms spiky underwater ‘carpets’ on the seabed, known as 'maerl beds’. As a type of 'coralline’ algae, maerl deposits lime in its cell walls as it grows, creating a hard, brittle skeleton.

Western Scotland’s famous white beaches are made not of coral but of fragments of dead maerl, crushed by the waves and bleached by the sun. Aggregations of living unattached maerl are often called ‘rhodoliths’.

Scotland’s two common species of maerl are hard to tell apart:

  • Phymatolithon calcareum is widespread
  • Lithothamnion glaciale is more northern in its range

On open coasts exposed to some waves, maerl grows as flattened discs. Where there’s less wave action, it often forms dense, branched, spiny nodules up to 10cm in diameter.

Fragile and slow growing, maerl can be damaged by dredging, heavy anchors and mooring chains. Maerl is expected to be adversely affected by rising temperatures and ocean acidification caused by climate change.

Map of maerl beds in the UK

An important habitat

In many areas of the west coast, and in sea loch narrows, extensive beds of living maerl develop above a deep gravel of dead white maerl. These maerl beds are an important habitat for many smaller marine plants and animals.

Animals that burrow in the maerl gravel beneath the living bed include:

  • bivalves
  • urchins
  • sea cucumbers
  • anemones
  • worms

Young scallops in particular seek out living maerl beds as nursery areas. Protecting maerl beds thus helps to sustain our scallop fishing industry. Yet scallop dredging has been shown to cause significant damage to maerl beds and to their associated species.

Maerl beds are also an important blue carbon store.

They are a priority marine feature in Scotland’s seas.

Maerl beds are also a protected feature of some Nature Conservation Marine Protected Areas, which help to conserve our most important marine wildlife, habitats and geodiversity.

Find out more

Learn more about maerl on the NBN Atlas Scotland website.