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Data analyses - Only those species with a mean abundance of 3 or more per core
were statistically analysed. The raw faunal data, together with the data from sediment
analyses and redox measurements, were tested for normality using the Anderson-
Darling test and for homogeneity of variance using the Bartlett test. Raw data, if
necessary, were transformed using an appropriate transformation to achieve normality
and homoscedasticity (Zar, 1984). A Two-sample t-test was then carried out on either
the raw or transformed data to assess if there were any significant differences between
the weed and the non-weed plots. A Mann-Whitney U test was carried out on any
variable not satisfying the parametric assumptions even after transformation. To
assess differences between the diversities of weed and non-weed plot communities, a
Hutcheson's modified t-test for Shannon-Wiener diversity index values was used,
following the recommendation of Zar (1984). The Hutcheson's modified t-test
requires first calculating the Shannon-Wiener diversity index values of the
communities by summing all replicates.
Size-frequency distributions were compared between treatments using the Two-
sample Kolmogorov-Smirnov (K-S) test and the x 2 goodness of fit test. Both tests
were used since although the former is more appropriate for the data (Zar, 1984), the
latter permits the identification of those sizes contributing most to any significant
differences. Size classes were grouped so that no expected values were below 5 for
the x2 test, as recommended by Elliot (1977).
All statistical analyses were performed using Minitab version 10.0 except the
Kolmogorov-Smirnov test which was carried out by hand using the formula for large
sample sizes given by Smirnov (1948). The Hutcheson's modified t-test was
performed by a program written by R. Ladle (pers. comm.).
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