Water Framework Directive Marine Plants Task Team Tools Paper ...

The application of the shore description is not as straight forward as the rest of the
metric components as it only acts as a correction for the level of species richness and
not the proportions of green, red, and opportunist or the ESG ratio. Its inclusion into
the metric as a single component bares too much weighting for the system, therefore it
only needs to be incorporated into the final species richness value. Using data from
reference or near reference conditions a graph was plotted to show the level of
correlation between species richness and shore description (Figure 8) displaying a
non­linear relationship between the two variables. This relationship can be described
by an exponential­type model of the form:
RICHNESS = a +
b exp(cSHORE )
where a, b and c are parameters to be estimated from the data. Using least squares,
these parameters were estimated to be:
a = 16.543
b = 7.150
c = 0.122
Therefore for each value of shore description there is a level of species richness that is
to be expected for reference conditions from which a ‘de­shoring factor’ has been
produced. This can be seen in table 3. This factor was based around an average shore
description of 15. The actual level of species richness can then be compare with the
predicted level of species richness by applying the ‘de­shoring factor’. An example is
given below:
The site of Bugel Bay in Northumberland has a shore description of 10 and a species
richness of 51. The expected level of species richness for this shore description is
40.73 with a de­shoring factor of 1.50. Therefore the final value for species richness
is:
RICHNESS = 51 x 1.50 = 76.50
This is the final value to be input to the metric system