- Monitoring change
In general terms as mentioned above the macro infauna will provide the best indicator
to the health of the systems. Reference to baseline data should be made to define a set of
stations for routine monitoring the numbers of which will be dictated by financial and
time considerations. In intertidal areas core samples on transects taken down the
intertidal zone should be taken. There is no clearly defined time of year for sampling as
summer months which provide ample daylight and amenable weather conditions are subject to
ephemeral populations of invertebrates and recruitment of juveniles. Established winter
populations may fluctuate due to storm events, heavy rainfall and freezing, the limited
hours of daylight is also a problem.
If samples are to be compared over time it is important that the sample time must not
vary from year to year and major weather events noted (Dalkin & Barnett, 1998).
Subtidally at representative stations grab sampling should be undertaken. In areas where
the epifaunal component is important use of trawls and towed or remote operated video
along set transects may be necessary. Subtidally the time of sampling is best carried out
around May as weather conditions are generally best from May to September and recruitment
generally occurs from February to May (Thomas, 1998). However weather conditions may
preclude this but it is important that samples are taken at as close to the same time of
year as possible.
The high cost of benthic sampling may mean that it is more practical to only work up a
reduced number of replicates or stations with the remainder being carried out to allow
full statistical analysis if some change is evident.
The frequency of monitoring will be largely determined by financial and time
constraints. Hiscock (1998a) recommends following a six year cycle for statutory sites
with a proportion of the sites e.g. those which have a particular scientific or
conservation interest monitored more regularly at least every three years. These
guidelines seem reasonable for the monitoring of the intertidal and subtidal SACs dealt
with here but this will depend on the size of the areas involved.
The characterisation of the community structure will involve separation of the main
trends within a multivariate data set. Each species and each physico-chemical parameter
constitutes a variable within the statistical analysis. It is often possible to
rationalise the species list to around ten important species which control the dynamics of
the community particularly if manipulation experiments are feasible or have been carried
out (Gray, 1981). Multivariate analysis of sites within the SACs e.g. techniques such as
TWINSPAN (Gauch, 1982) or the MDS and SIMPER routine in the PRIMER package (Warwick &
Clarke, 1994) identify groups of sites with similar composition and the indicator species
which are particularly well correlated to the assemblages found within the SAC. Replicate
samples will usually be required to allow detailed statistical analysis and significance