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Marine Habitat Classification

Description of biotope or habitat type

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   Sparse sponges, Nemertesia spp. and Alcyonidium diaphanum on circalittoral mixed substrata

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Moderately strong (1-3 kn)
Substratum Boulders; cobbles; pebbles
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.HCR.XFa.SpNemAdia Sparse sponges, <I>Nemertesia</I> spp. and <I>Alcyonidium diaphanum</I> on circalittoral mixed substrata

  • 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 is found on moderately wave-exposed sand-scoured, circalittoral boulders, cobbles and pebbles that are subject to moderately strong tidal streams (referred to as lag-cobbles locally). It is characterised by sparse sponges and a diverse bryozoan and hydroid turf. The sparse sponge community is primarily composed of Dysidea fragilis and Sycon ciliatum. The mixed faunal turf is composed of Nemertesia antennina, Nemertesia ramosa, Halecium halecinum, Sertularia argentea, Alcyonium digitatum, Bugulina flabellata, Bugulina turbinata, Crisularia plumosa, Flustra foliacea, Cellepora pumicosa, Alcyonidium diaphanum, Cellaria fistulosa and crisiid bryozoans. The anemones Epizoanthus couchii, Cylista elegans and Cerianthus lloydii may also be recorded. Echinoderms such as the starfish Asterias rubens, Crossaster papposus, Henricia oculata and the crinoid Antedon bifida. Other species present include the colonial ascidian Clavelina lepadiformis, the barnacle Balanus crenatus, the top shell Steromphala cineraria, the polychaete Spirobranchus triqueter, the ascidian Morchellium argus, Prosthecareus vittatus and the crab Cancer pagurus. It is distributed off Pen Llyn and over considerable areas of the Irish Sea.


No situation data available.

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
Nemertesia antennina 10 Occasional 81-100%
Alcyonium digitatum 6 Occasional 81-100%
Clavelina lepadiformis 5 Occasional 61-80%
Epizoanthus couchii 5 Occasional 61-80%
Bugulina flabellata 4 Occasional 61-80%
Asterias rubens 3 Occasional 61-80%
Flustra foliacea 3 Occasional 61-80%
Nemertesia ramosa 3 Occasional 61-80%
Alcyonidium diaphanum 2 Occasional 61-80%
Antedon bifida 2 Occasional 41-60%
Balanus crenatus 2 Common 41-60%
Bugulina turbinata 2 Occasional 41-60%
Cerianthus lloydii 2 Occasional 41-60%
Crossaster papposus 2 Occasional 41-60%
Dysidea fragilis 2 Occasional 41-60%
Cylista elegans 2 Frequent 41-60%
Crisularia plumosa 1 Occasional 21-40%
Cancer pagurus 1 Occasional 21-40%
Cellaria fistulosa 1 Common 21-40%
Cellepora pumicosa 1 Occasional 21-40%
Crisiidae 1 Frequent 21-40%
Steromphala cineraria 1 Occasional 41-60%
Halecium halecinum 1 Occasional 41-60%
Henricia oculata 1 Occasional 41-60%
Morchellium argus 1 Frequent 21-40%
Spirobranchus triqueter 1 Occasional 41-60%
Prostheceraeus vittatus 1 Rare 41-60%
Sycon ciliatum 1 Occasional 21-40%
Sertularia argentea 1 Occasional 21-40%

Similar biotopes or habitat types

This biotope occurs under more wave-exposed conditions subject to slightly weaker tidal streams. Flustra foliacea is present in higher abundances in CR.HCR.XFa.FluCoAs.X.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) CR.MCR.ByH.SNemAdia

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