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Marine Habitat Classification


Description of biotope or habitat type

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   Faunal and algal crusts 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), Very weak (negligible)
Substratum Bedrock, boulders, cobbles
Zone Circalittoral
Depth Band 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 Faunal and algal crusts 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 biotope typically occurs on the vertical and upper faces of wave-exposed and moderately wave-exposed circalittoral bedrock or boulders subject to mostly moderate to weak tidal streams (a variant of this biotope containing brittlestar is found on bedrock, boulders and cobbles). The biotope is dominated by faunal (e.g. Parasmittina trispinosa) and algal (Corallinaceae) crusts, and tends to have a grazed appearance; this may be partially attributable to the abundance of Echinus esculentus found in this biotope. Occasionally, the rock may appear pink from a distance, due to the expanses of encrusting red algae on the rock surface. Alcyonium digitatum is one of the few species to stand erect from the encrusted rock surface and are frequently encountered, on the tops of rocky outcrops and boulders. Hydroids do not form a prominent feature of this biotope, with only robust species such as Abietinaria abietina frequently recorded. Sponges and Caryophyllia smithii are rarely present while erect bryozoans and ascidians are scarce (although there are exceptions, see variants). The E. esculentus grazed substratum may be interspersed with other encrusting species such as the polychaete Pomatoceros triqueter and the saddle oyster Pododesmus patelliformis. Other species present include Asterias rubens, Ophiothrix fragilis, Urticina felina, Ophiocomina nigra, Pagurus bernhardus, Flustra foliacea, Gibbula cineraria, Calliostoma zizyphinum, Ophiura albida, Ciona intestinalis and Antedon bifida. Six variants of this biotope have been recorded. FaAlCr.Flu is dominated by the silt and scour tolerant bryozoan F. foliacea. FaAlCr.Adig is dominated by A. digitatum. FaAlCr.Sec is dominated by Securiflustra securifrons. FaAlCr.Pom looks extremely impoverished (even for a grazed community). FaAlCr.Bri has a dense covering of brittlestars while FaAlCr.Car is only found under weak/very weak tides and is dominated by C. smithii.

Situation

No situation data available.

Temporal variation

No temporal variation data available.

Characterising Species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Abietinaria abietina 3 Occasional 41-60 %
Alcyonium digitatum 12 Frequent 81-100 %
Urticina felina 3 Occasional 41-60 %
Pomatoceros triqueter 2 Common 61-80 %
Pagurus bernhardus 2 Occasional 21-40 %
Gibbula cineraria 2 Occasional 41-60 %
Calliostoma zizyphinum 1 Occasional 21-40 %
Pododesmus patelliformis 1 Occasional 21-40 %
Flustra foliacea 2 Frequent 21-40 %
Parasmittina trispinosa 2 Occasional 21-40 %
Antedon bifida 1 Occasional 21-40 %
Asterias rubens 9 Occasional 81-100 %
Ophiothrix fragilis 7 Frequent 61-80 %
Ophiocomina nigra 2 Frequent 21-40 %
Ophiura albida 1 Frequent 21-40 %
Echinus esculentus 13 Frequent 81-100 %
Ciona intestinalis 1 Occasional 21-40 %
Corallinaceae 10 Common 61-80 %

Similar biotopes

Not applicable or unknown.

Photos

CR.MCR.ECCR.FaAlCr Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock, NW of Hoxa Head, Scapa Flow. Sue Scott © JNCC
CR.MCR.ECCR.FaAlCr Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock, NW of Hoxa Head, Scapa Flow. Sue Scott © JNCC
CR.MCR.ECCR.FaAlCr Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock, Stacks of Scroo, Fair Isle. ANON © JNCC
CR.MCR.ECCR.FaAlCr Faunal and algal crusts on exposed to moderately wave-exposed circalittoral rock, Stacks of Scroo, Fair Isle. ANON © JNCC

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