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Nephtys hombergii's spatial distribution produced a significant correlogram (Figure
2.6v) even though its distribution was not significantly different from random (Table
2.2). The correlogram implies that N. hombergii formed patches between 1-1.5m2
which were 1.5-2m apart, this is supported by its density plot, Figure 2.5(viii).
Similarly, Thrush et al. (1989) found that some species which were randomly
distributed according to their indices of dispersion did in fact have significant spatial
structures.
Figures 2.5(ix-xii) display the spatial heterogeneity of % organic carbon, % silt/clay,
Md (1) and sorting coefficient. These sediment variables also appeared clumped:
patches of increased organic carbon and silt/clay contents, together with areas of
higher Md Os and sorting coefficients, were present. These patches appeared larger
than those formed by most of the faunal species analysed. The significant
correlograms presented in Figures 2.6(vi-ix) suggest spatial structures with patch sizes
1.5-2m2 for % organic content, % silt/clay and sorting coefficient and >3.5m 2 for Md
(1). Within these patches, sediments contained higher levels of these variables
compared to surrounding sediments. According to their contour plots, these 4
sediment variables appeared to have been positively correlated with each other in their
spatial distributions. A comparison of the spatial heterogeneity of these sediment
variables with those of the fauna must be made with caution due to the mis-match of
scales (see Methods). Although % organic content, % silt/clay and sorting coefficient
formed patches similar in size (1.5-2m 2) to many of the species the contour plots
suggest that they were not spatially correlated. This was formally tested for P. elegans
(Table 2.5) but the density plots suggest that this appears to have been the case for all
the other species.
Figures 2.5(i-xi) support the results of the correlation analyses. For example, high
density areas, or patches, of P. elegans did not occur in the same areas as those formed
by other species, nor did they appear in the same areas as high levels of the 4 sediment
variables.
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