Download (20MB) - Repository@Napier

out concurrent with the faunal experiment on the 18th December. Six patch and six
non-patch plots were chosen and defaunated sediments implanted into each in the
same way as for the faunal experiments. After 3 weeks, 1 core (2.4cm internal
diameter, 3cm deep) was taken from within each of the previously defaunated
sediments from each of the 12 plots. These samples were frozen and then later
analysed for water, organic and silt/clay contents. Redox potential values were
measured at 1, 2 and 4cm depths within each azoic sample, using the technique
described in Chapter 4. Water and organic contents were determined in an identical
way as described in Chapter 2. It was not possible to carry out a full particle size
distribution analysis on the sediments and, therefore, silt/clay fraction was determined
for each sample by wet sieving on a 63).tm sieve. This method was compared with
that used in Chapter 2 and although it produced higher % silt/clay fraction values it
gave much more consistent results within replicates.
Data analyses - The invertebrate data were analysed using both univariate and
multivariate techniques. For the univariate analysis, only those species with a mean
abundance of at least 2 for any plot type were regarded as sufficiently abundant for
statistical analysis. The data were checked for normality using the Anderson-Darling
test and homogeneity of variances by the Bartlett test. Any data not conforming to
either of these two were transformed using an appropriate transformation (Zar, 1984).
The transformed data were re-checked using the above tests, any data still not
conforming to either test were analysed using an appropriate non-parametric test.
Differences in means between azoic samples from patch plots and non-patch plots
were otherwise assessed using Two-sample t-tests.
The sizes of P. elegans (5th setiger width) and any other taxa with mean abundances
20 per core in either plot type were measured. C. cap itata individuals were
measured across their 3rd setiger (Ragnarsson, 1996). Size-frequency distributions
were tested for difference between patch and non-patch azoics using the Kolmogorov-
Smirnov (K-S) test and the X 2 goodness of fit test. The relative suitability of these,
and the advantage of using the latter test, are given in Chapter 4.
138