This review describes several causes of natural changes in rocky shore communities. All communities show some degree of temporal variability and many rocky shore communities show a good deal of natural fluctuations. The abundance of limpets, barnacles and Fucus plants may be relatively constant over a large area of shore. However, in a smaller area of that shore, an aggregation of limpets might be replaced by a patch of barnacles and then of Fucus plants over the course of a few years.

Connell and Sousa (1983 suggest that communities should be thought of in terms of their persistence within stochastically defined bounds. In other words, how long will an assemblage of species coexist, given the natural variability in their populations and will they continue to coexist after a natural perturbation? Clearly these questions are scale dependent; the area of interest should be defined before they are asked.

Chapter I describes the MNCR biotope classification scheme which describes areas according to a mixture of community and habitat characteristics. This scheme allows a characterisation of the shore at any instant. Any single description of the status of a community, however, cannot account for the temporal and spatial variation characteristic of natural ecosystems. These characteristics must be recognised and accounted for if management and conservation of rocky shores is to be effective. Ultimately, a well designed monitoring programme will be the best way to understand the spatial and temporal dynamic features of any given shore community.

The MNCR biotope scheme is likely to be widely used in the conservation and management of marine SACs. The appendix gives a qualitative assessment of the likely stability and persistence of the communities represented by the MNCR intertidal reef biotopes (full descriptions of each type are given in Connor et al., 1997). Interpretation of the results of single surveys couched in the terms of the biotope scheme must take account of the likely permanence (or transience) of each biotope. CAPITALS denote emphatic statements about the likely stability can be made.

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