Biodiversity & Conservation

Mytilus edulis and barnacles on very exposed eulittoral rock



Image Anon. - Close view of Mytilus and dense barnacles covering rock surface. Image width ca XX cm.
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Distribution map

LR.HLR.MusB.MytB 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

  • Mytilus edulis
  • Semibalanus balanoides
  • Littorina neglecta
  • Porphyra umbilicalis
  • Aglaothamnion sepositum
  • Ceramium shuttleworthianum
Community Importance Species name Common Name
Key structural Mytilus edulis Common mussel
Key structural Semibalanus balanoides An acorn barnacle
Key functional Patella vulgata Common limpet
Important functional Nucella lapillus Dog whelk
Important other Palmaria palmata Dulse
Important other Corallina officinalis Coral weed


Mytilus edulis and Semibalanus balanoides are effective competitors for space, modify the substratum surface and provide food, substratum and interstices for the associated community. Therefore, while the relative proportion of each species will vary with location, they have been included as key structural species. Grazing gastropods, especially limpets, have a strong influence on the abundance of macroalgae and the recruitment of other species, although importance of different grazers will vary with location and time. Therefore, Patella vulgata has been included as a key functional species and to represent the sensitivity of gastropods. Nucella lapillus is an important predator on barnacles and mussels and has been included as important functional. Palmaria palmata and Corallina officinalis have been included as important other to represent the sensitivity of the red algae that occur within the biotope.

Additional information

The MNCR recorded 289 species within this biotope (JNCC, 1999) although not all species occur in all examples of the biotope. The species composition of this biotope is likely to be variable. The relative abundance of the Mytilus edulis and Semibalanus balanoides probably depends on stochastic variation in recruitment, environmental conditions, and physical disturbance (e.g. by storms). The upper and lower limits are transitional with other biotopes that will vary with location, e.g. where the lower limits is transitional with e.g. ELR.Him, EIR.Ala or ELR.Coff, species characteristic of the lower shore or sublittoral fringe will probably penetrate the lower limit of this biotope increasing species richness. This biotope resembles the patchy, Mytilus edulis 'islands' (now thought to be Mytilus galloprovincialis (Seed, 1992)) described by Tsuchiya & Nishihira (1985 & 1986) on rocky shores in Japan, who provide species lists for their habitats.

This review can be cited as follows:

Tyler-Walters, H. 2002. Mytilus edulis and barnacles on very exposed eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 01/12/2015]. Available from: <>