Nature and importance of rocky littoral habitats

Annex I of the EU Habitats Directive identifies reef habitats as natural features which are important in conservation terms. In the present context, the word ‘reef’ is used simply to imply a hard substratum type. Thus the term intertidal reefs refers to rocky littoral habitats, commonly described as rocky shores. This report aims to provide a synthesis-oriented scientific review of rocky shore biotopes. This includes each of the littoral rock habitat complexes described by Connor et al (1997) with the exception of biogenic reefs (e.g. those produced by Sabellaria species) which are the subject of a separate marine SAC review (see Holt et. al., 1998). It also covers those sublittoral rock biotopes which are found in the sublittoral fringe.

Rocky shores are the major habitat on most of the coast from the Isle of Wight around Wales and Scotland to Flamborough Head. They are of considerable conservation importance as sites of high biodiversity. Most importantly they are well studied and understood using both observational and manipulative field experimental approaches. In the British Isles we are particularly fortunate to have a eloquent descriptive account of most types of rocky shore in Lewis (1964). We also have the extensive biogeographic surveys of major species made in the 1950s (e.g. Crisp and Southward, 1958). This has been followed by much experimental work including pioneering limpet removal experiments (Jones, 1948; Lodge, 1948) reviewed in Southward and Southward (1978) and Hawkins et al (1992) and summarised in recent textbooks (Hawkins and Jones, 1992; Raffaelli and Hawkins, 1996; Little and Kitching, 1996).

This work in both Britain and overseas has highlighted the major environmental gradients on shores (tidal elevation, wave action) and the importance of biological interactions in structuring shore communities. In the British Isles the functional influence of key species, such as limpet grazing on exposed shores and the structural role of the algal canopy on sheltered shores, have been demonstrated by field experiments (see Hawkins et al, 1992 for review). Biogeographic variation around Britain is also well known for most important species. Recruitment variation has also been shown to be an important factor in the dynamics of rocky shore systems (see Raffaelli and Hawkins, 1996 for review).

Communities of species on rocky shores are sensitive to a variety of both acute (e.g. oil spills) and chronic impacts (e.g. TBT-based paints, recreational activities). The responses of communities to these impacts is well understood enabling conservation measures to be proposed. The accessibility of rocky shores means they have a key role to play in conveying a strong conservation message to the general public. Many voluntary reserves use rocky shores in this way (e.g. Kimmeridge, Wembury, St Mary's Island). Their accessibility and two-dimensional structure makes them suitable for extensive surveillance and monitoring. Some rocky shore species are good indicators of climatic change. Monitoring marine protected areas with a wide spatial extent would enable detection of effects of climatic change (Southward, Hawkins and Burrows, 1995).

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