Biodiversity & Conservation

Faunal and algal crusts, Echinus esculentus, sparse Alcyonium digitatum and grazing-tolerant fauna on moderately exposed circalittoral rock



Image David Connor - Faunal and algal crusts, Echinus esculentus, sparse Alcyonium digitatum, Abietinaria abietina and other grazing-tolerant fauna on moderately exposed circalittoral rock. Image width ca 1m.
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Distribution map

CR.MCR.EcCr.FaAlCr.Pom recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats

For a list of 2004 characterising species please see the JNCC website.

Species indicative of sensitivity

To assess the sensitivity of the biotope, the sensitivity of component species is reviewed. Those species that are considered to be particularly indicative of the sensitivity of the biotope, and for which research has been undertaken in detail are shown below (see selection criteria). The biology of other component species of the biotope is also taken into account wherever information is known to the researcher.

Species found especially in this biotope

  • Echinus esculentus
  • Alcyonium digitatum
  • Caryophyllia smithii
  • Pododesmus patelliformis
  • Parasmittina trispinosa
  • Antedon bifida
  • Crossaster papposus
  • Asterias rubens
  • Clavelina lepadiformis
  • Pomatoceros triqueter
Community Importance Species name Common Name
Key functional Echinus esculentus Edible sea urchin
Important characterizing Alcyonium digitatum Dead man's fingers
Important other Lithophyllum incrustans Encrusting coralline algae
Important other Parasmittina trispinosa An enrusting bryozoan
Important other Pomatoceros triqueter A tubeworm


This biotope corresponds to the early successional epifaunal communities, with intense sea urchin grazing, dominated by encrusting algal crusts and faunal crusts (e.g. tubeworms and bryozoans) described by Sebens (1985, 1986). Sebens (1985, 1986) demonstrated epifaunal succession to faunal turf and eventually ascidian, Alcyonium or Metridium dominated communities after the removal of sea urchins. In similar experiments, Echinus esculentus was shown to control the lower limit of Laminaria species in the Isle of Man (Jones & Kain 1967; Kain 1979). Therefore, Echinus esculentus has been suggested as a key functional species, since its loss would result in major changes in the community. Alcyonium digitatum has been included as important characterizing since it occurs in most records of the biotope. Lithophyllum incrustans has been included to represent the encrusting coralline algae characteristic of the biotope. Parasmittina trispinosa and Pomatoceros triqueter are included as characteristic faunal crusts. In the absence of detailed research on Parasmittina trispinosa, reference was made to Electra pilosa and other bryozoans to represent its sensitivity.

Additional information

The MNCR recorded 497 species within this biotope although not all species occurred in all records of the biotope.

This review can be cited as follows:

Tyler-Walters, H. 2002. Faunal and algal crusts, Echinus esculentus, sparse Alcyonium digitatum and grazing-tolerant fauna on moderately exposed circalittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/11/2015]. Available from: <>