Biodiversity & Conservation

Overhangs and caves



Image Keith Hiscock - A well developed overhang community with pendulous polyclinid tunicates. Image width ca 1 m.
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Distribution map

LR.LR.Ov recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

  • EC_Habitats

Ecological and functional relationships

Species living under overhangs are mainly active suspension feeders relying on water-borne food and are not generally interacting. However, overgrowth of one species by another may occur (cf. Turner, 1988) and some overhangs become dominated by one species especially Dendrodoa grossularia. A small number of species feed on the encrusting fauna including, for example, Archidoris pseudoargus on sponges, the cowrie Trivia monacha spp on compound ascidians, and the dog whelk Nucella lapillus on barnacles.

Seasonal and longer term change

Changes are probably similar to those described by Foster-Smith (1989) for under-boulders where many encrusting ascidians increased in abundance by late summer on the Northumbrian coast.

Habitat structure and complexity

Overhangs vary greatly in their 'openness' and their aspect. They can be deeply overhanging and be more like small shallow caves with downward facing surfaces to being almost vertical surfaces. Also, rock type is important in determining the community that develops. Where soft rock (for instance, limestone or chalk) is present there is likely to be a high proportion of boring species in the rock.


Not researched

Recruitment processes

Mainly from planktonic larvae.

Time for community to reach maturity

Settlement panels, which attract similar communities to overhang habitats, may be fully colonized within about 18 months of being placed into the environment (extrapolated from Sutherland & Karlson 1977; Todd 1994). Development of 'mature' communities under overhangs is likely to occur within two years and there will be dynamic stability where the same species are always present but individuals and colonies die and recruit with time.

Additional information

No studies were found that specifically describe overhang and intertidal cave communities.

This review can be cited as follows:

Hiscock, K. 2002. Overhangs and caves. 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: <>