The littoral zone is the most accessible of all marine habitats. Since many rocky shore organisms can be easily identified in situ, non-destructive surveillance is usually possible (e.g. Lewis, 1976). Rocky shore monitoring therefore provides a cheap and efficient means of assessing the condition of coastal ecosystems.

Physical and biological characteristics of the shore and the relationship between them should be recorded whatever the ultimate aim of sampling. Important physical factors include shore elevation, wave exposure and topographical structure (see Chapter II). Many surveillance techniques treat the shore as two dimensional. Estimates of species or population density are based on the unit area surveyed. As topographical complexity increases, so will the surface area of the rock within a quadrat (Kostylev et al., 1996). Not accounting for surface complexity could introduce bias into surveillance data.

Sampling conducted on a single visit to the shore can answer questions about the community structure at one instant. Relevant questions might concern the types of organisms present and the abundance and distribution of each species. In order to determine the effects of natural events or human activities on ecological communities, it is important to determine how they change in response to these factors. Monitoring and surveillance schemes test the hypothesis that communities do not change over time. The obvious requirement of such schemes is repeated sampling. It is important to select the time of year and frequency of survey which will best meet the study objectives, and to repeat surveys at the same time each year to avoid confusing seasonal with interannual changes. A good time for such visits is between late summer and autumn, by which time the year’s cohort of most species will have settled. In the highly unlikely event that seasonal patterns are to be described, monthly or bimonthly sampling would be needed. A sampling frequency as low as four to six times a year would give some idea of seasonal differences between years.

Many communities are immensely variable in the absence of man-made perturbations. Such natural changes might result from biological effects. For example competition for space, grazing, predation, and recruitment variation can all affect the relative abundance of organisms (Chapter III). Alternatively, changes can be caused by physical perturbations such as storms, prolonged shifts in wind direction and unusual temperatures (Lewis, 1985). The effects of biological interactions are often localised, while changes due to physical factors usually affect much larger areas.

Those shores which show the greatest degree of natural fluctuation are easily perturbed in experiments. They are therefore likely to suffer the greatest impact from anthropogenic factors. This creates the non-trivial problem of detecting anthropogenic effects against a background of biologically induced fluctuations (Hawkins et al., 1985). It is certainly worth conducting surveillance on these shores. Good design is of paramount importance. Impacts close to the site of a pollution source might be easy to detect if they cause gross deviation from natural cycles.

However, a formal surveillance scheme should be used to identify more subtle, chronic or widespread impacts with a good degree of certainty. Surveillance should be carried out at several sites at different distances from sources of potential impact. A comparison of the results from each site will allow a sensible judgement to be made about the cause of observed changes. Attention should also be given to previous studies of disturbance and recovery (e.g. the aftermath of the Torrey Canyon oil spill) and to studies of the natural dynamics of rocky shore. Detection of changes associated with seasonal variation in communities require especially close attention to sampling design: with random sampling within seasonal periods (Underwood, 1997).

Many southern rocky shore species reach the northern limits of their distributions on the western coast of Britain and Ireland. A smaller number of northern species also reach their southern limits along this coast (e.g. Fucus distichus anceps in soutthwest Ireland). Past records have shown that some of these limits respond to climatic change, both gradually (e.g. Southward, 1991) and rapidly due to unusually extreme weather (e.g. Crisp 1964). Thus rocky shores provide the potential for monitoring climatic change, provided monitoring is carried out at a series of stations spread over a wide geographic range. The assignment of Marine SAC status to a number of sites throughout the latitudinal range of the British coast and the proper monitoring of such sites could allow the achievement of this aim by providing a network of sites.

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