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.
Biological and Physical
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.
Survey design and
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
years 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.
Biological variability and
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).
Distribution of Species
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.