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RESULTS
Univariate analysis of species abundances - A total of 14 and 15 taxa were recorded
in the patch and non-patch azoic samples respectively, from the April, August and
December experiments. Of these, only 5 were sufficiently abundant for statistical
analysis. These were the polychaetes P. elegans and C. capitata, the bivalves C. edule
and M. balthica, and oligochaetes (mainly tubificids). Their mean densities after 3
weeks colonisation, together with standard errors and the results of statistical testing
between the two plot types (Two-sample t-test) are shown in Figures 6.2 (i-vii).
Pygospio elegans adults colonised the azoic sediments within 3 weeks in very low
numbers. In the August and December experiments, adult P. elegans densities in
patch samples were higher, although not statistically significant, from those in non-
patch samples.
In contrast to the adults, juvenile P. elegans colonised the azoic sediments in
relatively high numbers when ready-to-settle larvae were present in the water column.
This was the case during April when a large peak in P. elegans settlement occurred at
Drum Sands (see Chapter 3). At this time, a mean density of 32.3 ± 3.7 juveniles per
core colonised the patch plots. Moreover, this was statistically higher than the number
of juveniles, 20 ± 3.5 per core, successfully colonising non-patch plots, see Figure
6.2(ii). In August, the numbers of juveniles colonising azoic sediments were much
lower and in contrast to the situation in April, their numbers were significantly higher
in non-patch samples. Larval settlement was lower during December in both patch
and non-patch plots, despite a second recruitment peak in the population at Drum
Sands in December (Chapter 3). This disparity may have been due to the fact that
samples for Chapter 3 were taken at the start of December, while this experiment was
not started until the 18th of December, suggesting the acute recruitment phase
recorded in Chapter 3 terminated early in December.
Capitella capitata colonised azoic sediments within 3 weeks in relatively high
numbers in all three experimental periods. This species was the only one to increase
in numbers in the treated sediments compared to numbers in ambient sediments taken
at the same time (see Figure 6.2(iv) and Figure 8.1(iv)), although this was not
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