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Marine Habitat Classification


Description of biotope or habitat type

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   Mixed kelp and red seaweeds on infralittoral boulders, cobbles and gravel in tidal rapids


Habitat (physical) description

Salinity Full (30-35 ppt), Variable (18-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams Very strong (>6 kn), Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum Boulders, cobbles and gravel
Zone Infralittoral
Depth Band 0-5 m, 5-10 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 IR.MIR.KT.XKTX Mixed kelp and red seaweeds on infralittoral boulders, cobbles and gravel in tidal rapids

  • 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

Mixed substrata of boulders, cobbles, pebbles and gravel, typically found in tidal rapids with kelp Laminaria saccharina and Laminaria hyperborea and red seaweeds. L. saccharina usually dominates this habitat although L. hyperborea may occur in equal abundance at some sites. The kelp in these tidal rapids does not form the same dense canopies associated with stable tide-swept bedrock, but generally occurs at lower abundance (Frequent). Other brown seaweeds occur in significant amounts in these tidal rapids including Dictyota dichotoma, Halidrys siliquosa and Chorda filum. These mixed substrata support a greater diversity of species than scoured bedrock narrows (XKT). In particular, there is an increase in red algal species such as Corallina officinalis, Bonnemaisonia hamifera and Ceramium nodulosum, although none occur in any great abundance. Red seaweeds common to both XKT and this biotope include Chondrus crispus, Delesseria sanguinea, Plocamium cartilagineum and Phycodrys rubens. Good examples of this biotope often have maerl gravel (Lithothamnion sp.) or rhodoliths between cobbles and boulders. Where maerl dominates, the biotope should be recorded as a maerl bed (SS.SMP.Mrl). The sponges associated with more stable, tide-swept conditions are generally absent, but the anthozoan Anemonia viridis might be present. Cobbles and pebbles are encrusted by the ubiquitous polychaete Pomatoceros triqueter and provide shelter for scavenging crabs such as Carcinus maenas and the hermit crab Pagurus bernhardus, gastropods such as Gibbula cineraria and echinoderms such as Echinus esculentus, Asterias rubens, Ophiocomina nigra and Ophiothrix fragilis which favour these sites of increased water movement. Additional infaunal species, inhabiting the sediment pockets, include Lanice conchilega and Sabella pavonina, which can be locally abundant.

Situation

Where stable rock fringes the shallows the tide-swept Laminaria digitata biotope often occurs (LdigT). Adjacent areas of stable bedrock or boulders in these sheltered, tide-swept narrows can support a similar kelp community, often with a greater percentage of L. hyperborea (XKT). Maerl fragments are often found amongst the mixed substrata of XKTX and this biotope may abut more extensive areas of maerl bed (Phy & Lgla).

Temporal variation

Unknown.

Characterising Species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Anemonia viridis 2 Occasional 41-60 %
Pomatoceros triqueter 10 Frequent 61-80 %
Pagurus bernhardus 3 Occasional 41-60 %
Carcinus maenas 5 Frequent 41-60 %
Gibbula cineraria 1 Frequent 41-60 %
Asterias rubens 6 Occasional 61-80 %
Ophiothrix fragilis 1 Occasional 21-40 %
Ophiocomina nigra 4 Common 41-60 %
Echinus esculentus 2 Occasional 41-60 %
Bonnemaisonia hamifera 2 Frequent 21-40 %
Corallinaceae 3 Frequent 41-60 %
Corallina officinalis 2 Occasional 41-60 %
Lithothamnion 9 Common 81-100 %
Chondrus crispus 3 Rare 61-80 %
Ceramium nodulosum 2 Rare 41-60 %
Delesseria sanguinea 1 Occasional 41-60 %
Phycodrys rubens 3 Occasional 41-60 %
Rhodophycota indet.(non-calc.crusts) 1 Frequent 21-40 %
Dictyota dichotoma 3 Frequent 41-60 %
Laminaria hyperborea 1 Frequent 21-40 %
Laminaria saccharina 11 Frequent 81-100 %
Halidrys siliquosa 1 Occasional 21-40 %
Ulva lactuca 4 Occasional 41-60 %

Similar biotopes

IR.HIR.KSed.XKHal
This biotope occurs on the open coast in deeper water.

IR.MIR.KT.XKT
Stable, tide-swept rock in the sheltered narrows and sills of Scottish sealochs, characterised by a dense kelp forest of L. hyperborea (Common) and/or Laminaria saccharina (Frequent) on scoured, coralline-encrusted rock. The brown seaweed Chorda filum is not present. Filterfeeders like the sponge Halichondria panicea, hydroids (Obelia geniculata) and anthozoans like Urticina felina and Sargartia elegans are present (Frequent-Occasional) due to the more stable substrata of this biotope compared to XKTX.

Biotope history

Classification Habitat code
Lsac.T (in part)

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