Biodiversity & Conservation

Underboulder communities



Image Keith Hiscock - Underboulder community dominated by sponges from a rock pool habitat. Wembury, South Devon. Image width ca 1 m.
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Distribution map

LR.MLR.BF.Fser.Fser.Bo recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats
  • UK_BAP

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

Rare of scarce species associated with this biotope

Community Importance Species name Common Name
Important other Pisidia longicornis Long-clawed porcelain crab
Important other Umbonula littoralis An encrusting bryozoan
Important structural Botryllus schlosseri Star ascidian
Important other Dendrodoa grossularia Baked bean ascidian
Important structural Halichondria panicea Breadcrumb sponge
Important other Balanus crenatus An acorn barnacle


The structure of MLR.Fser.Fser.Bo communities is likely to vary greatly between boulders. As a result many of the species chosen as indicative to sensitivity have been listed as 'important other', since other designations suggest the species plays a permanent central role in the biotope. A representative of the groups of organisms most likely to be found in the biotope at a given time has been selected, bearing in mind the difference between frequently disturbed and seldom disturbed boulder communities (see Ecological and Functional Relationships).

The breadcrumb sponge Halichondria panicea and star ascidian Botryllus schlosseri have both been listed as important structural species since they are competitively superior to many encrusting bryozoan species likely to occur in underboulder communities. A solitary ascidian, Dendrodoa grossularia, has also been included since its represents a species that is likely to be found in larger boulders that have undergone considerable succession in terms of community development. Umbonula littoralis has been included as a representative of the various encrusting bryozoans likely to be found in MLR.Fser.Fser.Bo. The acorn barnacle Balanus crenatus, along with bryozoans and colonial ascidians, will be an important early colonizer of the rock surface and is likely to be one of the pioneer species on smaller frequently disturbed boulders. Apart from filter feeders, the dominant trophic group, the long-clawed porcelain crab, Pisidia longicornis scavenger has been listed as important other since it is likely to be found in and around the sediment that under the boulder. The broad-clawed porcelain crab Porcellana platycheles may be more commonly associated with MLR.Fser.Fser.Bo than Pisidia longicornis although more information was available for the long-clawed porcelain crab.

In undertaking this assessment of sensitivity, account is taken of knowledge of the biology of all characterizing species in the biotope. However, 'indicative species' are particularly important in undertaking the assessment because they have been subject to detailed research.

Additional information

Underboulder communities are especially described in Foster-Smith (1989, 1991), Foster-Smith & Foster-Smith (1987), and Hiscock (1984) and in various reports produced during the MNCR survey of Scottish sea lochs.

This review can be cited as follows:

Hiscock, K. 2005. Underboulder communities. 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: <>