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8m survey - spatial patterns
Figures 2.7(i-viii) present the interpolated density maps of the non-randomly
distributed species from the 8m survey while Figures 2.8(i-v) display the significant
correlograms. The distance classes 1-6 for these correlograms represent inter-sample
distances of 0-8m, 8-12m, 12-16m, 16-20m, 20-24m and 24-28m, respectively. The
density maps suggest that 2 species appeared to form patches less than 8m 2 (E. cf
flava and G. duebeni; both of which produced non-significant correlograms) while the
other species either formed patches between 8-24m 2 (C. capitata, S. martinensis and
L. conchilega) or patches of various sizes (P. elegans). The correlograms do not
appear to support the density plots for all species. For example, while the density plot
for L. conchilega (Figure 2.7(iii)) suggests a patch of approximately 20m 2 was
present, the correlogram (Figure 2.8(ii)) implies a patch size of only 8-12m2.
Areas of increased densities of some species, C. edule and M. balthica for example,
were located at the edges of the 56x56m survey area and therefore it is not possible to
give an indication of patch sizes from the density plots and one must be cautious when
drawing conclusions from their correlograms.
Figures 2.7(i-xii) support the results of the correlation analyses (Table 2.5). The non-
significant correlations between P. elegans and most of the other species are clearly
defended by the maps since high density patches of most species do not seem to have
been spatially correlated within the survey area. Furthermore, the significant positive
correlation between P. elegans and M. balthica is vindicated by their contour plots,
although the locations of moderate M. balthica densities as well as high densities have
to be observed to see this.
Figures 2.7(ix-xii) suggest that the 4 measured sediment variables were spatially
correlated with each other to a certain extent. Increased levels of organic carbon and
silt/clay, together with Md 0 and sorting coefficient were mainly found at the top of
the 56x56m grid, although high levels of organic carbon content and Md (I) were also
found in other small areas. The significant correlograms produced for the distribution
of these variables (except % organic content) in Figures 2.8(vi-viii) indicate patch
sizes of approximately 20-24m 2. However, since these were located at the edges of
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