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
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).