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Marine Habitat Classification

Description of biotope or habitat type

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   Alaria esculenta forest with dense anemones and crustose sponges on extremely exposed infralittoral bedrock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed
Tidal streams Weak (>1 kn)
Substratum Bedrock
Zone Infralittoral
Depth Band 10-20 m, 20-30 m, 30-50 m
Other Features Vertical, very steep rock and

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat IR.HIR.KFaR.AlaAnCrSp <I>Alaria esculenta</I> forest with dense anemones and crustose sponges on extremely exposed infralittoral bedrock

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.


This biotope has only been recorded from Rockall, where Alaria esculenta appears to replace Laminaria hyperborea as the dominant kelp forest species on the extremely wave-exposed steep and vertical rock, a zone that extends from 14 m down to 35 m. Beneath the A. esculenta canopy, the rock surface is covered by a dense turf of anthozoans such as Cylista elegans, Phellia gausapata and Corynactis viridis, encrusting sponges and coralline algae. The gastropod Margarites helicinus can be found grazing on the kelp fronds, whereas the crab Cancer pagurus can be found among the kelp stipes. The bryozoan Tubularia indivisa also occur, but it does not form such a dense turf as in more shallow waters, while the ascidian Botryllus leachi is found encrusting the large brown seaweeds. Cryptopleura ramosa is the dominant red seaweed on horizontal surfaces. The kelp Laminaria digitata is reported to occur mixed with A. esculenta on the nearby Helen's reef.


Above the AlaAnSC zone (about 5 m to 13 m) A. esculenta still dominates, but it resembles more closely the typical sublittoral fringe A. esculenta biotope (Ala.Myt), though it has a very dense turf of small hydroids and few foliose algae. Towards the lower part of this A. esculenta forest (30 m to 35 m), the density of A. esculenta is reduced and the rock surface is characterised by a dense turf of red algae (FoR).

Temporal variation


Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Corynactis viridis 15 Common 81-100%
Alaria esculenta 14 Abundant 81-100%
Cylista elegans 11 Frequent 81-100%
Phellia gausapata 10 Frequent 81-100%
Tubularia indivisa 8 Frequent 81-100%
Cryptopleura ramosa 7 Frequent 61-80%
Botrylloides leachii 6 Frequent 61-80%
Cancer pagurus 5 Occasional 61-80%
Didemnidae 4 61-80%
Corallinaceae 3 61-80%
Margarites helicinus 3 Frequent 61-80%
Amphipoda 2 61-80%
Porifera indet crusts 2 41-60%

Similar biotopes or habitat types

Not applicable or unknown.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) EIR.AlaAnSC
1996 (6.95) EIR.AlaRAn
1996 (6.95) EIR.RAn

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