Biodiversity & Conservation

Halidrys siliquosa and mixed kelps on tide-swept infralittoral rock with coarse sediment.



Image Rohan Holt - Halidrys on flat pebbles and gravel. Image width ca 1 m.
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Distribution map

IR.MIR.SedK.HalXK recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats

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

  • Esperiopsis fucorum
  • Aglaophenia pluma
  • Delesseria sanguinea
  • Dilsea carnosa
  • Halidrys siliquosa
Community Importance Species name Common Name
Important characterizing Halidrys siliquosa Sea oak
Important structural Delesseria sanguinea Sea beech
Important structural Chondrus crispus Carragheen
Important structural Furcellaria lumbricalis A red seaweed
Important structural Saccharina latissima Sugar kelp
Important structural Botryllus schlosseri Star ascidian
Important structural Aglaophenia pluma A hydroid


This biotope is characterized by the abundance of Halidrys siliquosa, without which the biotope would not be recognised. Laminarians may also be present, the exact species varying with location. Therefore, Saccharina latissima has been chosen to represent their sensitivity. Similarly, the community is composed of silt tolerant red algae species, therefore, Chondrus crispus, Furcellaria lumbricalis, and Delesseria sanguinea have been included as important structural to represent red algal species. The biotope also contains a diverse epiphytic fauna, especially on Halidrys siliquosa, which are characteristic of tidally swept conditions. Therefore, Botryllus schlosseri and has been included as important structural to represent their sensitivity. Reference was made to Nemertesia ramosa to represent hydroids.

Additional information

The MNCR recorded ca 734 species within this biotope, although not all species occurred in all records of the biotope. Halidrys siliquosa dominated communities are also described by Lewis (1964) and additional records provided by Dixon et al. (1978).

This review can be cited as follows:

Tyler-Walters, H. 2002. Halidrys siliquosa and mixed kelps on tide-swept infralittoral rock with coarse sediment.. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29/11/2015]. Available from: <>