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RESULTS
Univariate analysis of species abundances - A total of 22 taxa for the patch samples
and 20 for non-patch samples were recorded from the 4 sampling months, only 6 of
these were sufficiently abundant for univariate statistical analysis (i.e., mean
abundances 2 for either plot type). These were the polychaetes P. elegans and C.
capitata, the bivalves C. edule and M. balthica, the amphipod C. volutator and
oligochaetes. Mean densities, together with standard errors and statistical differences
between patch and non-patch densities, are presented in Figures 8.1(i-viii). Statistical
analysis was not carried out on total P. elegans numbers since they were the sums of
the adult and juvenile means and these stages were analysed separately. Statistical
analysis was not carried out for C. capitata, C. volutator and oligochaetes for August
1998 due to insufficient numbers in the samples.
The numbers of adult P. elegans were always significantly higher in patches than
outside patches (Figure 8.1(i)). Since the sampling was stratified into patches and
non-patches this result is not surprising. Their numbers increased from April to
December 1997 in both plot types. However, in August 1998, there was a large
decrease in the numbers of P. elegans adults both inside and outside patches from 72
+ 8.4 to 13.6 ± 2.34 and 37.8 ± 2.76 to 4.3 ± 1.13; for patch and non-patch samples
respectively. Juvenile P. elegans densities were high during April 1997 as this
coincided with the peak of new recruits for this year (see Chapter 3). Their densities
were much lower the following August but increased again in December 1997,
corresponding to a second, smaller peak of new recruits during the winter (see Chapter
3). Their numbers were again low in August 1998. Additionally, the numbers of
juveniles in patches and non-patches were never significantly different, suggesting
there was no preferential juvenile recruitment to the ambient sediments of patches
compared with non-patch areas (this contrasts with the findings of Chapter 6 with
respect to azoic sediments).
The densities of C. capitata were relatively low during April and August 1997,
approximately 5 per core. However, there was a dramatic increase in their densities
during December when densities rose to 44.8 ± 5.1 and 30.7 ± 7.9 per core in patch
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