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Marine Habitat Classification

Description of biotope or habitat type

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   Laminaria digitata and piddocks on sublittoral fringe soft rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock
Zone Sublittoral fringe
Depth Band Lower shore
Other Features Soft rock such as chalk and limestone

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.KR.Ldig.Pid <I>Laminaria digitata</I> and piddocks on sublittoral fringe soft 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.


Soft rock, such as chalk, in the sublittoral fringe characterised by Laminaria digitata and rock-boring animals such as piddocks Barnea candida and Pholas dactylus, the bivalve Hiatella arctica and worms Polydora spp. Beneath the kelp forest, a wide variety of foliose red seaweeds occur such as Palmaria palmata, Chondrus crispus, Membranoptera alata and Halurus flosculosus. Filamentous red seaweeds often present are Vertebrata fucoides and Ceramium nodulosum, while coralline crusts cover available rock surface. The bryozoan Membranipora membranacea and the hydroid Dynanema pumila can form colonies on the kelp fronds, while the bryozoan Electra pilosa more often occur on the foliose red seaweeds. Empty piddock burrows are often colonised by the polychaete Sabellaria spinulosa or in more shaded areas the sponges Halichondria panicea and Hymeniacidon perlevis. The undersides of small chalk boulders are colonised by encrusting bryozoans, colonial ascidians and the tube-building polychaete Spirobranchus lamarcki. The boulders and any crevices within the chalk provide a refuge for small crustaceans such as Carcinus maenas, the mussel Mytilus edulis or the barnacle Semibalanus balanoides. The echinoderm Asterias rubens is present as well.


This biotope occurs on moderately exposed soft rock where Ldig.Ldig would normally occur. Above it may lie a zone of Fucus serratus on similarly bored soft rock (Fser.Pid) or a variant of one of the F. serratus biotopes (Fser.R or Fser.Fser). Lower shore sites influenced by sand may have more Mytilus edulis beneath the seaweed canopy (MytFR) or the sand-binding red seaweed Rhodothamniella floridula (Rho). Below the Ldig.Pid biotope a variety of biotopes can occur such as LsacChoR on unstable infralittoral cobbles and boulders or even MCR.Pid in the turbid waters of south-east England where the kelp generally extends to less than 4m BCD.

Temporal variation

The under-storey of foliose and filamentous seaweeds will diminish towards the autumn and regrow in the spring. Since the soft rock does not provide a strong hold for the seaweeds they are easily dislodged during storm periods. After such an event the green seaweeds Enteromorpha spp. and Ulva spp. and/or the red seaweed P. palmata may temporarily cover much of the rock. Eventually a more diverse range of seaweeds and associated animals will re-establish on the rock.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Laminaria digitata 14 Abundant 81-100%
Polydora 9 Abundant 81-100%
Electra pilosa 7 Common 81-100%
Hiatella arctica 5 Frequent 81-100%
Pholas dactylus 5 Common 61-80%
Dynamena pumila 4 Occasional 61-80%
Palmaria palmata 4 Common 61-80%
Amphipoda 3 Common 61-80%
Chondrus crispus 3 Common 61-80%
Halichondria panicea 3 Occasional 61-80%
Vertebrata fucoides 3 Frequent 61-80%
Membranipora membranacea 2 Occasional 41-60%
Semibalanus balanoides 2 Occasional 61-80%
Corallinaceae 2 Abundant 41-60%
Corallina officinalis 2 Common 41-60%
Hymeniacidon perlevis 2 Occasional 61-80%
Mytilus edulis 2 Occasional 61-80%
Asterias rubens 1 Occasional 61-80%
Barnea 1 Common 41-60%
Carcinus maenas 1 Occasional 41-60%
Ceramium nodulosum 1 Common 21-40%
Spirobranchus lamarcki 1 Occasional 61-80%
Sabellaria spinulosa 1 Common 41-60%

Similar biotopes or habitat types

Dense canopy of L. digitata on exposed to sheltered sublittoral fringe bedrock or boulders often with a wide range of filamentous and foliose red seaweeds beneath. Without the rock-boring fauna such as piddocks B. candida, P. dactylus and P. pholadiformis, the bivalve H. arctica and worms Polydora spp. associated soft rock biotopes.

Classification history of this biotope or habitat type

Classification version Code

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