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Marine Habitat Classification


Description of biotope or habitat type

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   Alcyonium digitatum with dense Tubularia indivisa and anemones on strongly tide-swept circalittoral rock


Habitat (physical) description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed
Tidal streams Very strong (>6 kn), Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum bedrock; boulders
Zone Circalittoral - lower, Circalittoral - upper
Depth Band 5-10 m, 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.FaT.CTub.Adig <I>Alcyonium digitatum</I> with dense <I>Tubularia indivisa</I> and anemones on strongly tide-swept 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 exposed circalittoral bedrock and boulders in sounds, narrows and around tide-swept promontories in accelerated tidal streams. It is dominated by aggregations of dead man's fingers Alcyonium digitatum, and dense clumps or continuous cover of the robust hydroid Tubularia indivisa, particularly on prominent ledges and ridges. Anemones such as Sagartia elegans, Urticina felina, Metridium senile, Actinothoe sphyrodeta and Corynactis virdis form a prominent component of the community. Occasionally, massive sponges such as Pachymatisma johnstonia and Esperiopsis fucorum may be present. Encrusting species such as the polychaete Pomatoceros triqueter and the barnacle Balanus crenatus may be dotted around the rocks, and the top shell Calliostoma zizyphinum may also be observed. Clumps of the bryozoan Flustra foliacea are occasionally seen. The starfish Asterias rubens may be seen amongst a patchy turf of Crisia denticulata and the bryozoan Alcyonidium diaphanum. This variant may also be found on tideswept wrecks and other artificial sustratum.

Situation

Above this biotope, it is usual to find well-developed kelp forest in the upper infralittoral, dominated by Laminaria hyperborea (LhypR). In the lower infralittoral, it is usual to find a tide-swept turf of hydroids and red algae.

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
Pachymatisma johnstonia 3 Occasional 41-60 %
Esperiopsis fucorum 2 Frequent 21-40 %
Tubularia indivisa 27 Common 81-100 %
Alcyonium digitatum 21 Frequent 81-100 %
Urticina felina 3 Frequent 41-60 %
Metridium senile 2 Frequent 21-40 %
Sagartia elegans 6 Common 61-80 %
Actinothoe sphyrodeta 1 Frequent 21-40 %
Corynactis viridis 3 Common 21-40 %
Pomatoceros triqueter 2 Frequent 21-40 %
Balanus crenatus 1 Common 21-40 %
Calliostoma zizyphinum 2 Occasional 41-60 %
Crisia denticulata 1 Occasional 21-40 %
Alcyonidium diaphanum 2 Frequent 21-40 %
Flustra foliacea 2 Occasional 41-60 %
Asterias rubens 7 Occasional 61-80 %

Similar biotopes

CR.HCR.FaT.CTub.CuSp
This biotope occurs on slightly more wave-sheltered sites than CTub.Adig. However, they are both subject to generally similar, strong tidal streams. CTub.CuSp also tends to be found slightly deeper. Although a similar suite of hydroid species are found in both biotopes, CTub.CuSp has a more diverse range of sponges, ascidians, and turf-forming bryozoans such as Bugula spp. In addition, dense colonies of A. digitatum are found in CTub.Adig.

CR.HCR.FaT.BalTub
This biotope tends to be found across a broader range of wave-exposures compared to Tub.Adig. However, they are both subject to similar tidal-streams. BalTub also tends to be found on a wider range of substratum types compared to CTub.Adig. BalTub has a 'bare' appearance, dominated by T. indivisa and B. crenatus, whereas CTub.Adig has a more diverse range of sponges, ascidians, and turf-forming bryozoans.

Biotope history

Classification Habitat code
97.06 CR.ECR.Alc.AlcTub

Photos

CR.HCR.FAT.CTub.Adig Alcyonium digitatum with dense Tubularia indivisa and anemones on strongly tide-swept circalittoral rock, Firth of Lorn. David Ainsley © JNCC
CR.HCR.FAT.CTub.Adig Alcyonium digitatum with dense Tubularia indivisa and anemones on strongly tide-swept circalittoral rock, Firth of Lorn. David Ainsley © JNCC

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