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Multivariate analysis of community structure - The complete species matrices were
used for multivariate analyses and these are summarised in Table 6.3. In total, 15
species colonised the azoic sediments within 3 weeks, although the majority of these
were found in very low numbers.
Pygospio elegans (adult) Eteone cfflava
Pygospio elegans (juvenile) Anaitides mucosa
Capitella capitata Glycera tridactyla
Cerastoderma edule Scoloplos armiger
Macoma balthica Fabulina fabula
Polydora cornuta Nephtys hombergii
Streblospio benedicti oligochaetes
Spio martinensis polynoids
Table 6.3 : Total species list from patch and non-patch azoic samples for all three
experiments.
The dendrograms produced by hierarchical agglomerative clustering, together with the
2-dimensional ordination plots produced by non-metric MDS of the resulting
communities from the April, August and December experiments are given in Figures
6.5-6.12. The stress values associated with these MDS ordinations varied from 0.04
to 0.18. Although there is no critical cut-off value for stress values above which a
species matrix cannot be represented adequately in a 2-dimensional MDS plot, the
lower the stress the better. Warwick and Clarke (1994) suggested that stress values
between 0.1-0.2, as the majority of those in the present study, give 'only potentially
useful 2-dimensional pictures'. Under these circumstances, they recommended that
the MDS plot should be complemented with other techniques such as clustering.
Therefore, for ordinations with stress values between 0.1-0.2 dendrograms are
included since they can potentially aid interpretation of the MDS plots. However,
superimposition of the cluster groups at arbitrary similarity levels from the
dendrograms onto the ordination plots, as outlined by Warwick and Clarke (1994),
was not performed since this tends to add discrete subdivisions onto a community
continuum. To investigate community differences between patches and non-patches,
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