Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock

English name: Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock

Quick facts

EUNIS habitat type code A3.1111
Bern Convention Included in a Resolution 4 habitat type at a higher level (A3)

Description (English)

Very exposed sublittoral fringe bedrock characterised by the kelp Alaria esculenta and dense patches of small individuals of the mussel Mytilus edulis, both of which grow over a dense cover of encrusting coralline algae. Foliose red seaweeds may also be present, but the species composition and their abundance vary between sites. Species such as Corallina officinalis occur widely. The kelp Laminaria digitata is usually absent, although stunted plants may be present at a few sites. The limpet Patella vulgata and the barnacle Semibalanus balanoides are often common. Patches of anthozoans and the hydroid Tubularia spp. occur in more wave-surged areas. In extremely exposed areas the A. esculenta zone can extend as deep as 15 m, where it has less S. balanoides, M. edulis and greater densities of Tubularia spp. (e.g. Barra and shallow areas of Rockall, Scotland).
Situation: This biotope is most commonly found beneath the mussel-barnacle zone (unit A1.111) of very exposed shores and above the upper infralittoral Laminaria hyperborea forest ( A3.113 or A3.115). It is at the extremely wave-surged sites, such as St Kilda, that A3.113 occurs below A3.1111. Occasionally, the A. esculenta zone occurs below a narrow but dense band of red seaweeds: typically Mastocarpus stellatus and/or Palmaria palmata and Corallina officinalis (unit A1.125) or very occasionally Himanthalia elongata (A1.123). A dense turf of C. officinalis (A1 122) occurs above the A. esculenta zone at a few extremely exposed sites, particularly on steep or vertical rock. On less exposed shores, however, an A. esculenta dominated zone may lie immediately above a narrow L. digitata zone (A3.1112). Unit A3.1111 can also occur on less exposed steep or vertical shores, where wave-surge restricts the growth of L. digitata which generally dominates the sublittoral fringe rock on moderately exposed shores. On seasonally unstable boulders or sites subject to disturbance by strong wave-action, a mixed kelp canopy that characterises A3.122 may occur beneath the A3.1111 zone instead of the ubiquitous L. hyperborea forest; this is most common on the Shetland isles.
Temporal variation: At very exposed sites, A. esculenta may have been so wave-battered during the season as to be reduced to a tattered midrib with no blades, altering the general appearance of the biotope. Where A3.1111 occurs on boulders and/or sites subject to disturbance during severe weather conditions, rock that is scoured clean may then be rapidly colonised by fast-growing green algae such as Enteromorpha spp. An assemblage of rapidly colonising species that characterise the disturbed A3.121 biotope may also develop in the sublittoral fringe. A species that can fluctuate in huge numbers at these sites is the starfish Asterias rubens, sometimes forming dense aggregations across the narrow A. esculenta band whilst feeding on the mussels.

Source: EUNIS habitat classification

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Species mentioned in habitat description

Algae Alaria esculenta
Invertebrates Asterias rubens
Algae Corallina officinalis
Algae Himanthalia elongata
Algae Laminaria digitata
Algae Laminaria hyperborea
Algae Mastocarpus stellatus
Invertebrates Mytilus edulis
Algae Palmaria palmata
Invertebrates Patella vulgata
Invertebrates Semibalanus balanoides
Species scientific name English common name Species group
Alaria esculenta Algae
Asterias rubens Invertebrates
Corallina officinalis Algae
Himanthalia elongata Algae
Laminaria digitata Algae
Laminaria hyperborea Algae
Mastocarpus stellatus Algae
Mytilus edulis Invertebrates
Palmaria palmata Algae
Patella vulgata Invertebrates
Semibalanus balanoides Invertebrates

Other classifications

Classification Code Habitat type name Relationship type
Marine Habitat Classification Britain/Ireland 0405 IR.HIR.KFaR.Ala.Myt <I>Alaria esculenta</I>, <I>Mytilus edulis</I> and coralline crusts on very exposed sublittoral fringe bedrock source
CORINE Land Cover 5.2.3. Sea and ocean n/a
For relation to plant communities (syntaxa), see Vegetation types

History

Classification Code Habitat type name Relationship type
EUNIS Habitat Classification 200410 A3.1111 Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock same
EUNIS Habitat Classification 200308 A3.1111 Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock same
EUNIS Habitat Classification 200202 A3.1111 Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock same
EUNIS Habitat Classification 199910 A3.1111 Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock same
MNCR BioMar 97.06 (Britain & Ireland) EIR.KFaR.Ala.Myt Alaria esculenta, Mytilus edulis and coralline crusts on very exposed sublittoral fringe bedrock same
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