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Marine Habitat Classification

Description of biotope or habitat type

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   Mixed turf of bryozoans and erect sponges with Sagartia elegans on tide-swept ciraclittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn)
Substratum Bedrock; boulder
Zone Circalittoral - lower, Circalittoral - upper
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.HCR.XFa.ByErSp.Sag Mixed turf of bryozoans and erect sponges with <I>Sagartia elegans</I> on tide-swept ciraclittoral 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 wave-exposed circalittoral bedrock and boulders, on steep slopes and upper faces in moderate tidal streams. This species-rich biotope is characterised by a dense sponge, hydroid and bryozoan turf and frequent Alcyonium digitatum. There are frequently large growths of Cliona celata and Pachymatisma johnstonia. Other species present in this diverse sponge community include Polymastia boletiformis, Haliclona viscosa, Polymastia mamilliaris, Scypha ciliata, Hemimycale columella and Dysidea fragilis. Axinellid sponges such as Stelligera stuposa and Raspailia ramosa may be present in low abundance, and are usually more abundant in deeper water. A dense hydroid turf forms a significant part of this biotope, with tufts of large hydroids such as Nemertesia antennina and Nemertesia ramosa frequently recorded. Other hydroid turf component species include Halecium halecinum, Aglaophenia tubulifera and Abietinaria abietina. Anemones are also well represented, with species such as Urticina felina, Sagartia elegans and Metridium senile recorded. The cup coral Caryophyllia smithii and the anemone Corynactis viridis are also frequently seen. The bryozoan turf is composed predominantly of Alcyonidium diaphanum and Flustra foliacea, whilst crustose species such as Parasmittina trispinosa contribute to a lesser extent. The delicate Bugula plumosa may also be present. There is a significant echinoderm component in this biotope. Species such as the starfish Asterias rubens, Henricia oculata, Marthasterias glacialis and Luidia ciliaris, the sea urchin Echinus esculentus and the crinoid Antedon bifida are all regularly recorded. Other species which may be observed include the top shell Calliostoma zizyphinium, the colonial ascidian Clavelina lepadiformis and the barnacle Balanus crenatus. The crab Cancer pagurus is typically found under boulders. This variant has been recorded from from various sites including Pembrokeshire, the Calf of Man and the west coast of Ireland.


Dense kelp forests containing L. hyperborea and S. polyschides are typically found above ByErSp.Sag.

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
Scypha ciliata 1 Occasional 61-80 %
Pachymatisma johnstonia 1 Occasional 61-80 %
Polymastia boletiformis 2 Frequent 61-80 %
Polymastia mamillaris 1 Frequent 41-60 %
Stelligera stuposa 1 Occasional 41-60 %
Cliona celata 4 Frequent 81-100 %
Hemimycale columella 1 Occasional 41-60 %
Haliclona viscosa 2 Occasional 61-80 %
Dysidea fragilis 1 Occasional 41-60 %
Halecium halecinum 2 Frequent 61-80 %
Abietinaria abietina 1 Occasional 41-60 %
Nemertesia antennina 5 Frequent 81-100 %
Nemertesia ramosa 3 Frequent 81-100 %
Aglaophenia tubulifera 1 Frequent 41-60 %
Alcyonium digitatum 6 Frequent 81-100 %
Urticina felina 3 Occasional 81-100 %
Metridium senile 1 Frequent 41-60 %
Sagartia elegans 2 Frequent 61-80 %
Corynactis viridis 2 Frequent 61-80 %
Caryophyllia smithii 3 Frequent 81-100 %
Balanus crenatus 2 Frequent 61-80 %
Cancer pagurus 1 Occasional 61-80 %
Calliostoma zizyphinum 3 Occasional 81-100 %
Alcyonidium diaphanum 2 Occasional 61-80 %
Flustra foliacea 2 Frequent 41-60 %
Bugula plumosa 1 Occasional 41-60 %
Parasmittina trispinosa 1 Frequent 41-60 %
Antedon bifida 2 Frequent 61-80 %
Luidia ciliaris 2 Occasional 61-80 %
Henricia oculata 3 Occasional 81-100 %
Asterias rubens 3 Occasional 81-100 %
Marthasterias glacialis 2 Occasional 61-80 %
Echinus esculentus 3 Occasional 81-100 %
Clavelina lepadiformis 2 Occasional 61-80 %

Similar biotopes or habitat types

This biotope occurs under similar conditions and depths as ByErSp.Sag. A diverse group of sponges, hydroids and bryozoans are found in both biotopes, but it is the frequently recorded Eunicella verrucosa and the occasional presence of Parazoanthus axinellae and Isozoanthus sulcatus that distinguishes it from ByErSp.Sag.

This biotope occurs under similar wave-exposure conditions with stronger tides than ByErSp.Sag. Also, ByErSp.DysAct is found at slightly shallower depths than ByErSp.Sag. Both biotopes have similar suites of species but distinct geographical distributions: ByErSp.DysAct only tends to be found off Wales and Lundy whereas ByErSp.Sag is usually found off the west coast of Ireland.


CR.HCR.XFA.ByErSp.Sag Mixed turf of bryozoans and erect sponges with Sagartia elegans on tide-swept ciraclittoral rock, Rathlin Island. Rohan Holt © JNCC
CR.HCR.XFA.ByErSp.Sag Mixed turf of bryozoans and erect sponges with Sagartia elegans on tide-swept ciraclittoral rock, Rathlin Island. Rohan Holt © JNCC

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