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Marine Habitat Classification


Description of biotope or habitat type

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   Faunal and algal crusts with Pomatoceros triqueter and sparse Alcyonium digitatum on exposed to moderately wave-exposed circalittoral rock


Habitat (physical) description

Salinity Full (30-35 ppt)
Wave exposure Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock, boulders, cobbles
Zone Circalittoral
Depth Band 5-10 m, 10-20 m, 20-30 m, 30-50 m
Other Features

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 CR.MCR.EcCr.FaAlCr.Pom Faunal and algal crusts with <I>Pomatoceros triqueter</I> and sparse <I>Alcyonium digitatum</I> on exposed to moderately wave-exposed circalittoral rock

  • 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.

Description

This variant is typically found on the upper faces of exposed and moderately exposed circalittoral bedrock or boulders subjected to moderately strong to weak tidal streams. From afar, the seabed has a rather sparse, grazed appearance, reminiscent of a brittlestar bed after the brittlestars have moved elsewhere. The rocky substratum is generally covered with encrusting red algae and the white, calcareous tubes of the polychaete Pomatoceros triqueter, dotted with the abundant urchin Echinus esculentus. Under closer inspection, Alcyonium digitatum are usually seen attached to the rocky surface underneath rock overhangs and large boulders. Although they may be recorded as abundant or common in some areas, their relatively small size means that their biomass is generally lower than in other biotopes. Sparse clumps of robust hydroids such as Abietinaria abietina are frequently observed, and bryozoan crusts such as Parasmittina trispinosa are occasionally seen. Echinoderms such as the brittlestars Ophiothrix fragilis and Ophiocomina nigra, and the crab Cancer pagurus may be seen within crevices in the boulders/rock whilst the starfish Asterias rubens may be seen on the rock surface. Muddy-gravel patches between boulders (especially within Scottish sealochs) provide a suitable habitat for the anemone Urticina felina. The top shell Gibbula cineraria is occasionally seen grazing on the rock surface. Within this biotope, there is some regional variation. The robust hydroid A. abietina is typically found in higher abundances in northern (Scottish) regions, especially around the Isle of May.

Situation

Above the FaAlCr.Pom variant in the infralittoral zone, species such as Alaria esculenta and Laminaria hyperborea are found in more wave exposed sites (KFaR.Ala/KFaR.Lhyp) while species such as Laminaria saccharina may be found above FaAlCr.Pom in the more sheltered examples. Due to moderately tide-swept conditions this variant is found in, clean, coarse sediment biotopes are generally found below FaAlCr.Pom. Typical species found in these coarse sand/gravelly biotopes include Neopentadactyla mixta and Lanice conchilega (SS.SMx.CMx). Where wave exposure increases, this variant tends to change to CarSp.PenPcom,, dominated by Caryophyllia smithii, Corynactis viridis, encrusting red algae and bryozoan crusts. Where tidal stream and wave-exposure decreases, this variant develops into a similar biotope dominated by encrusting red algae, Echinus esculentus and C.smithii (FaAlCr.Car).

Temporal variation

Not known.

Characterising Species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Abietinaria abietina 4 Frequent 41-60 %
Alcyonium digitatum 8 Frequent 61-80 %
Urticina felina 2 Occasional 41-60 %
Pomatoceros triqueter 9 Common 81-100 %
Pandalus montagui 1 Occasional 21-40 %
Cancer pagurus 1 Rare 21-40 %
Gibbula cineraria 2 Occasional 41-60 %
Parasmittina trispinosa 3 Occasional 41-60 %
Asterias rubens 10 Occasional 81-100 %
Ophiothrix fragilis 11 Occasional 81-100 %
Ophiocomina nigra 1 Occasional 21-40 %
Echinus esculentus 18 Frequent 81-100 %
Rhodophycota 1 Common 21-40 %
Corallinaceae 13 Common 61-80 %

Similar biotopes

CR.MCR.EcCr.FaAlCr.Car
This sub-biotope occurs on wave-exposed to wave-sheltered sites subject to only weak tidal streams. It is similar to FaAlCr.Pom in that it is relatively barren, but has a higher diversity of species, and has frequently occurring C. smithii and bryozoan crusts.

CR.MCR.EcCr.FaAlCr.Adig
This sub-biotope occurs on more wave-exposed sites, but is subject to similar tidal streams as FaAlCr.Pom. Both these sub-biotopes are very impoverished with a similar range of species, although FaAlCr.Adig tends to have much higher densities of A. digitatum than FaAlCr.

CR.LCR.BrAs.AmenCio.Ant
This biotope occurs in sheltered sea lochs, subject to weak/very weak tidal streams. This biotope is similar to FaAlCr.Pom in that it is relatively barren; heavily grazed by E. esculentus. Pink coralline crusts and large solitary ascidians are the prevalent species found.

Biotope history

Classification Habitat code
97.06 CR.MCR.GzFa.FaAlC

Photos

CR.MCR.ECCR.FaAlCr.Pom Faunal and algal crusts with Pomatoceros triqueter and sparse Alcyonium digitatum on exposed to moderately wave-exposed circalittoral rock, SE Blue Caps, farnes. Teresa Bennett © JNCC
CR.MCR.ECCR.FaAlCr.Pom Faunal and algal crusts with Pomatoceros triqueter and sparse Alcyonium digitatum on exposed to moderately wave-exposed circalittoral rock, SE Blue Caps, farnes. Teresa Bennett © JNCC
CR.MCR.ECCR.FaAlCr.Pom Faunal and algal crusts with Pomatoceros triqueter and sparse Alcyonium digitatum on exposed to moderately wave-exposed circalittoral rock, SE Blue Caps, Farnes. Teresa Bennett © JNCC
CR.MCR.ECCR.FaAlCr.Pom Faunal and algal crusts with Pomatoceros triqueter and sparse Alcyonium digitatum on exposed to moderately wave-exposed circalittoral rock, SE Blue Caps, Farnes. Teresa Bennett © JNCC

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