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Marine Habitat Classification


Description of biotope or habitat type

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   Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock


Habitat (physical) description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed, Moderately exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock, boulders
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.Adig <I>Alcyonium digitatum</I>, <I>Pomatoceros triqueter</I>, algal and bryozoan crusts on 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 vertical, steep and upper faces of wave-exposed circalittoral bedrock or boulders subject to varying amounts of current. The variant has a very grazed, sparse appearance, dominated only by the presence of Alcyonium digitatum and large expanses of encrusting red alage and bryozoan crusts particularly (Parasmittina trispinosa). The sparse appearance can be attributed to the frequently observed sea urchin Echinus esculentus. The polychaete Pomatoceros triqueter can be locally abundant, and may in some cases cover far more rock surface than A. digitatum, especially on vertical faces. Clumps of robust hydroids such as Abietinaria abietina occur occasionally. Other species present include the echinoderms Asterias rubens, Henricia sanguinolenta, Ophiothrix fragilis, the anemone Urticina felina, Calliostoma zizyphinum and Cancer pagurus.

Situation

Shallower than this biotope, dense kelp forest is typically found, containing species such as Laminaria hyperborea and Alaria esculentus. Occasionally, this biotope may be found on rocky outcrops surrounding by coarse sand. With this increased scour, MCR.UrtScr may develop at the rock/sand interface. Below this biotope, coarse sediments, muddy gravel and sand are typically recorded.

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 2 Occasional 41-60 %
Alcyonium digitatum 22 Abundant 81-100 %
Urticina felina 3 Occasional 41-60 %
Pomatoceros triqueter 17 Common 81-100 %
Cancer pagurus 1 Rare 41-60 %
Calliostoma zizyphinum 2 Occasional 41-60 %
Parasmittina trispinosa 2 Occasional 41-60 %
Henricia 2 Occasional 21-40 %
Asterias rubens 6 Occasional 61-80 %
Ophiothrix fragilis 2 Occasional 41-60 %
Echinus esculentus 13 Frequent 81-100 %
Rhodophycota 1 Frequent 21-40 %
Corallinaceae 12 Common 61-80 %

Similar biotopes

CR.MCR.EcCr.CarSp.PenPcom
This biotope occurs at slightly more exposed, deeper sites with weaker tidal streams. However, they are both found on similar substratum. FaAlCr.Adig has a much less diverse, impoverished fauna than CarSp.PenPcom possibly due to grazing pressure from E. esculentus. CarSp.PenPcom has a more diverse range of sponges, hydroids and bryozoans.

CR.MCR.EcCr.FaAlCr.Sec
This biotope is found under slightly less exposed conditions, subject to weaker tidal streams. FaAlCr.Sec is also found at slightly shallower water depths than FaAlCr.Adig. Although both biotopes are similarly quite clean and grazed, FaAlCr.Sec has a more diverse hydroid and bryozoan turf, with Securiflustra securifrons dominating.

CR.HCR.XFa.CvirCri
This biotope is found under similar conditions as FaAlCr.Adig. Like FaAlCr.Adig, this biotope has dense A. digitatum. However, CvirCri has a diverse sponge community.

CR.HCR.FaT.CTub.Adig
This biotope is found on extremely wave-exposed, extremely tide-swept bedrock or boulders. This biotope is similarly species poor, but is characterised by Tubularia indivisa.

Biotope history

Classification Habitat code
97.06 CR.ECR.Alc.AlcC

Photos

CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, Stacks of Scroo, Fair Isle. Sue Hiscock © JNCC
CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, Stacks of Scroo, Fair Isle. Sue Hiscock © JNCC
CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, St. Abbs lighthouse, St. Abbs Head. Rohan Holt © JNCC
CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, St. Abbs lighthouse, St. Abbs Head. Rohan Holt © JNCC
CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, Inner Hirst, Berwick. Jon Davies © JNCC
CR.MCR.ECCR.FaAlCr.Adig Alcyonium digitatum, Pomatoceros triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock, Inner Hirst, Berwick. Jon Davies © JNCC

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