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Marine Habitat Classification


Description of biotope or habitat type

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   Polyclinum aurantium and Flustra foliacea on sand-scoured tide-swept moderately wave-exposed circalittoral rock


Habitat (physical) description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock; boulder; cobble
Zone Circalittoral - lower, Circalittoral - upper
Depth Band 5-10 m, 10-20 m, 20-30 m
Other Features Occurs mainly on upper-faces.

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.FluCoAs.Paur <I>Polyclinum aurantium</I> and <I>Flustra foliacea</I> on sand-scoured 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.

Description

This variant is typically found on the upper face of moderately exposed, moderately tide-swept, circalittoral bedrock or boulders. Sand and silt are periodically re-suspended in the water column, resulting in scour-tolerant species being characteristic of these areas. There is a dense covering of the scour-resistant bryozoan Flustra foliacea attached to the bedrock plains and boulders. The colonial ascidian Polyclinum aurantium commonly covers the rock surface at most locations within this biotope - itself incorporating sand grains into its surface to give it the appearance of sandy rock nodules. Other ascidians that may occur in this crust are the flat, encrusting colonial Botrylloides leachi, Botryllus schlosseri and the colonial ascidian Clavelina lepadiformis, although in varying quantities at each location. A short turf of other bryozoans such as Alcyonidium diaphanum, Bugula plumosa and Bugula flabellata occur amongst the ascidians. Other species found in this biotope are the sponges Cliona celata, Leucosolenia botryoides and Scypha ciliata, the hydroids Tubularia indivisa, Nemertesia antennina, Halecium halecinum and the anthozoans Alcyonium digitatum and Urticina felina. Echinoderms which may be present include the starfish Asterias rubens, Crossaster papposus and the brittlestar Ophiothrix fragilis. Crustaceans such as the crab Cancer pagurus, the hermit crab Pagurus bernhardus and the lobster Homarus gammarus may be observed in crevices and under boulders. The palps of the polychaete Polydora spp. may be observed whilst the nudibranch Janolus cristatus may be seen preying on the hydroid/bryozoan turf. This variant is commonly found on the Northumberland coast, Flamborough Head and the Lleyn Peninsula.

Situation

As FluCoAs.Paur tends to occur in waters with a sediment load, the resulting light penetration is reduced, meaning that kelp forests such as Lhyp, normally found shallower than FluCoAs.Paur in the infralittoral zone, are present over a narrower depth range.

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
Leucosolenia botryoides 5 Frequent 61-80 %
Scypha ciliata 4 Frequent 81-100 %
Cliona celata 6 Common 81-100 %
Tubularia indivisa 1 Occasional 41-60 %
Halecium halecinum 2 Common 41-60 %
Nemertesia antennina 2 Occasional 61-80 %
Alcyonium digitatum 4 Common 81-100 %
Urticina felina 3 Frequent 81-100 %
Polydora 2 Frequent 41-60 %
Homarus gammarus 1 61-80 %
Pagurus bernhardus 1 61-80 %
Cancer pagurus 3 Occasional 61-80 %
Janolus cristatus 2 Occasional 61-80 %
Alcyonidium diaphanum 5 Frequent 81-100 %
Flustra foliacea 10 Common 81-100 %
Bugula flabellata 3 Occasional 61-80 %
Bugula plumosa 4 Common 61-80 %
Crossaster papposus 4 Occasional 81-100 %
Asterias rubens 6 Common 81-100 %
Ophiothrix fragilis 3 Frequent 81-100 %
Clavelina lepadiformis 3 Common 61-80 %
Polyclinum aurantium 8 Common 81-100 %
Botryllus schlosseri 1 Occasional 61-80 %
Botrylloides leachi 1 Occasional 61-80 %

Similar biotopes

CR.HCR.XFa.Mol
This biotope occurs on more heterogeneous substrata, composed of bedrock ridges with cobbles and sand plains, rather than predominantly bedrock in the case of FluCoAs.Paur. Both biotopes contain F. foliacea and a similar hydroid turf, but Mol lacks the diversity of sponges and the dense polyclinid ascidians. It is the dense aggregations of Molgula manhattensis which distinguish this biotope from others.

CR.HCR.XFa.FluCoAs.SmAs
This variant occurs on slightly more wave-exposed sites but subject to similar tidal streams. Both biotopes are found on the upper faces of circalittoral bedrock and boulders. Although both biotopes feature F. foliacea as a dominant feature of their fauna, FluCoAs.SmAs has a much more diverse associated sponge fauna and lacks the abundant sheets of the colonial ascidian Polyclinum aurantium.

CR.HCR.XFa.FluCoAs.X
This variant occurs on slightly more wave-exposed sites but subject to similar tidal streams. While FluCoAs.Paur is found on circalittoral bedrock or boulders, FluCoAs.X occurs on mixed substrata (boulders, cobble, pebble and gravel). Although both biotopes feature F. foliacea as a dominant feature of their fauna, FluCoAs.X has a much more diverse associated fauna and lacks the abundant sheets of the colonial ascidian Polyclinum aurantium.

CR.MCR.EcCr.FaAlCr.Flu
This biotope is found under similar exposure and tidal stream regimes as FluCoAs.Paur but occurs in slightly deeper water depths. FaAlCr.Flu is also found on similar rocky substrata as FluCoAs.Paur. While F. foliacea is the dominant bryozoan present in both, it is the presence of dense aggregations of Polyclinium aurantium which distinguish FluCoAs.Paur from this biotope.

Biotope history

Classification Habitat code
97.06 CR.MCR.As.StoPaur

Photos

CR.HCR.XFA.FluCoAs.Paur Polyclinum aurantium and Flustra foliacea on sand-scoured tide-swept moderately wave-exposed circalittoral rock, W Carreg Rhosan. Keith Hiscock © JNCC
CR.HCR.XFA.FluCoAs.Paur Polyclinum aurantium and Flustra foliacea on sand-scoured tide-swept moderately wave-exposed circalittoral rock, W Carreg Rhosan. Keith Hiscock © JNCC

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