Description of biotope or habitat type

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   Foliose red seaweeds on exposed lower infralittoral rock

Description

A dense turf of foliose red seaweeds on exposed or moderately exposed lower infralittoral rock, generally, at or below the lower limit of the kelp. Most of the red seaweeds are common to the kelp zone above, while the faunal component of the biotope is made up of species that are found either in the kelp zone or the animal-dominated upper circalittoral below. Foliose species commonly present include Dilsea carnosa, Hypoglossum hypoglossoides, Schottera nicaeensis, Cryptopleura ramosa and Delesseria sanguinea. The red seaweed species composition varies considerably; at some sites a single species may dominate (particularly Plocamium cartilagineum). Small filamentous red seaweeds can be found here as well. These include species such as Heterosiphonia plumosa, Vertebrata byssoides. As well as a varied red seaweed component, this biotope may also contain occasional kelp plants and patches of the brown foliose seaweed Dictyota dichotoma. Coralline crusts covers the bedrock beneath the seaweeds. The fauna generally comprises low-encrusting forms such as the tubeworms Spirobranchus spp., anthozoans including Alcyonium digitatum, Urticina felina and Caryophyllia smithii) and occasional sponge crusts such as Cliona celata, Amphilectus fucorum, Sycon ciliatum and Dysidea fragilis. More mobile fauna include the gastropod Calliostoma zizyphinum, the echinoderms Echinus esculentus as well as the starfish Asterias rubens and Marthasterias glacialis and lastly, the crab Cancer pagurus. Bryozoan crusts such as Electra pilosa can be found fronds on the foliose red seaweeds while scattered hydroids such as Nemertesia antennina form colonies on shells, cobbles and available rock. At some sites erect bryozoans Crisia spp. and Bugula spp. are present. Ascidians such as Clavelina lepadiformis and Clavelina lepadiformis may also be common. In the north the foliose red seaweed Metacallophyllis laciniata may occur.

Situation

This biotope is generally found at or below the lower limit of the kelp, below either kelp forest or park (LhypR.Ft and LhypR.Pk).

Temporal variation

Many of the red seaweeds, which occur in this biotope, have annual fronds, which tend to die back in the autumn and regenerate again in the spring. This produces a seasonal change in the density of the seaweed cover, which is substantially reduced over winter months and reaches its most dense between April to September.

Characterising species

Similar biotopes or habitat types

IR.HIR.KFaR.FoR.Dic

This biotope occurs in similar depth and conditions as IR.HIR.KFaR.FoR but is confined to SW coasts. The abundance of the brown seaweeds Dictyopteris polypodioides (Frequent) and D. dichotoma is higher (Common) with the Occasional presence of the kelps Laminaria hyperborea and Saccharina latissima.

IR.MIR.KR.XFoR

This biotope occurs on shallow, silted infralittoral bedrock and boulders in areas of turbid water dominated by dense red seaweeds, with the notable absence of kelp. Individual species of red seaweeds such as Plocamium cartilagineum or Calliblepharis ciliata often dominate. The fauna is both less diverse and has a lower abundance.

SS.SMp.KSwSS.SlatR.CbPb

This biotope occurs on mixed, mobile substrata and is characterised by red seaweeds such as Halarachnion ligulatum, Lomentaria orcadensis, Naccaria wiggii and Compsothamnion thuioides which thrive in these conditions.

Classification history of this biotope or habitat type