Maerl is a collective term for several species
of red seaweed, with hard, chalky skeletons. It is rock hard and,
unlike other seaweeds, it grows as unattached rounded nodules or
short, branched shapes on the seabed. Like all seaweeds,
maerl needs sunlight to grow, and it only occurs to a depth of
Maerl can form large beds, when the conditions
are right – a fast tidal flow or sufficient wave action to remove
fine sediments, but not strong enough to break the brittle maerl
branches. Within these beds, layers of dead maerl build up
with a thin layer of pink, living maerl on the top.
Maerl beds are an important habitat for many
different types of marine life, which live amongst or are attached
to the surface of Maerl, or burrow in the coarse gravel of dead
maerl beneath the top living layer. Maerl beds can be of importance
to sustainable fisheries, providing nursery grounds for commercial
species of fish and shellfish.
Due to the fragility of maerl, the beds are
easily damaged and have probably declined substantially in some
areas. Pressures on maerl beds include scallop dredging,
bottom trawling, aquaculture and pollution. Maerl beds are very
slow to develop and are unlikely to return if removed or lost. As
such, they should be treated as a non-renewable resource.
In England, the Fal and Helford Special Area
of Conservation includes the largest maerl beds in south-west
For the official habitat definition please see
the documents listed below.
Maerl beds are found off the southern and
western coasts of Britain and Ireland, as far north as Shetland,
and are particularly well developed around the Scottish islands and
in sea loch narrows, around Orkney, and in the south in the Fal
Estuary. Maerl beds occur within the wider north-east
Atlantic, as far as Iceland, and also in the Mediterranean.
- This is a UK BAP Priority Habitat (BAP
habitats are now Habitats of Principal Importance/Priority
- Listed in Annex I of the Habitats
- OSPAR List of Threatened
and/or Declining Species and Habitats (Region
III – Celtic Sea)
- Certain types of maerl species found
within the beds are UKBAP Priority Species, and species of principal importance for the purpose of
conservation of biodiversity under the Natural Environment and
Rural Communities Act 2006.
UK Biodiversity Action Plan; Priority Habitat Descriptions. BRIG
(ed. Ant Maddock) 2008 (updated December 2011)
Descriptions of habitats on the OSPAR list of threatened and/or
declining species and habitats (OSPAR agreement 2008/07).
UK Biodiversity Action Plan - Maerl beds
OSPAR Commission –
Background Document for Maerl beds
JNCC - UK BAP Priority
Species and Habitats
Marine Life Information Network - Maerl beds
JNCC EUNIS habitat correlations table