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Marine Habitat Classification

Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock

Physical habitat 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
Zone Circalittoral
Depth Band 10-20 m, 20-30 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.Sec <I>Alcyonium digitatum</I> with <I>Securiflustra securifrons</I> on tide-swept 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.


This variant is typically found on the upper and vertical faces of moderately wave-exposed circalittoral bedrock subject to moderately strong to weak tidal streams. The rock surface is dominated by Alcyonium digitatum and the bryozoan Securiflustra securifrons. The rock between these species appears fairly sparse and grazed, with expanses of encrusting red algae. The sea urchin Echinus esculentus is frequently seen, and in collaboration with the light attenuating effects of depth, is probably the principal reason for the lack of algal turf. Other species found include the hydroids Abietinaria abietina, Nemertesia antennina, Thuiaria thuja, the bryozoans Cellepora pumicosa, Parasmittina trispinosa, Flustra foliacea, Alcyonidium diaphanum and other bryozoan crusts. Encrusting species such as the polychaete Pomatoceros triqueter and the barnacle Balanus balanus are frequently observed. Other species present include Asterias rubens, Antedon bifida, Ophiura albida, Ophiothrix fragilis, Caryophyllia smithii, Urticina felina, Clavelina lepadiformis, Calliostoma zizphinium and Pandalus montagui.


Above this biotope, you tend to find exposed kelp forest and park (LhypR). There is a tendency for slight scouring to occur in this biotope. However, if this scour increases further, for example if water movement increases, mobilising more sand, this biotope may graduate into UrtScr. In more silty sites, there is a tendency for S. securifrons to be replaced by F. foliacea as the dominant bryozoan, turning the biotope into FaAlCr.Flu.

Temporal variation

Whilst the great majority of species in this variant are most likely present throughout the year, C. lepadiformis grows in spring and may show great variation in abundance from year to year.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Porifera 1 Frequent 41-60 %
Abietinaria abietina 3 Frequent 61-80 %
Thuiaria thuja 2 Occasional 41-60 %
Nemertesia antennina 2 Frequent 41-60 %
Alcyonium digitatum 14 Common 81-100 %
Urticina felina 2 Occasional 61-80 %
Caryophyllia smithii 3 Frequent 41-60 %
Pomatoceros triqueter 5 Frequent 61-80 %
Balanus balanus 1 Occasional 41-60 %
Pandalus montagui 1 Frequent 21-40 %
Calliostoma zizyphinum 1 Occasional 41-60 %
Bryozoa 1 Frequent 41-60 %
Alcyonidium diaphanum 1 Occasional 21-40 %
Flustra foliacea 1 Occasional 21-40 %
Securiflustra securifrons 12 Frequent 81-100 %
Parasmittina trispinosa 2 Occasional 41-60 %
Cellepora pumicosa 2 Occasional 41-60 %
Antedon bifida 3 Common 41-60 %
Asterias rubens 6 Frequent 81-100 %
Ophiothrix fragilis 2 Common 41-60 %
Ophiura albida 3 Frequent 41-60 %
Echinus esculentus 4 Frequent 61-80 %
Clavelina lepadiformis 2 Frequent 41-60 %
Corallinaceae 4 Occasional 61-80 %

Similar biotopes or habitat types

This biotope occurs on slightly more exposed sites subject to slightly stronger tidal streams. Although both biotopes are similarly quite clean and grazed, FaAlCr.Sec has a more diverse hydroid and bryozoan turf, with S. securifrons dominating.

This biotope occurs under similar conditions as FaAlCr.Sec. FaAlCr.Flu is also found on a slightly more mixed substratum. F. foliacea, and to a lesser extent A. digitatum are the dominant species within this biotope whereas in FaAlCr.Sec, S. securifrons and A. digitatum dominate. FaAlCr.Flu also tends to have a more silty appearance whereas FaAlCr.Sec appears clean and grazed.

Classification history of this biotope or habitat type

Classification version Code
97.06 CR.ECR.Alc.AlcSec


CR.MCR.ECCR.FaAlCr.Sec Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock, ENE Emanuel Head, Berwick. Rohan Holt © JNCC
CR.MCR.ECCR.FaAlCr.Sec Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock, ENE Emanuel Head, Berwick. Rohan Holt © JNCC

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