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emoved since they were the only taxa which colonised in sufficient numbers for size-
frequency determination (see later). Very few young stages of the other
macroinvertebrate species could be observed passing through this sieve. The 3-12cm
fractions of the samples were sieved on a 500).tm mesh sieve before preserving. These
samples, from the treated sediments, are hereafter referred to as `azoic' samples.
One sample (control core, Figure 6.1) from each plot was also taken at the same time
as the azoic sample. The results from these samples will not be presented here. They
will be referred to, however, where necessary to give background information on
faunal densities in ambient sediments. The results from these samples form part of
Chapter 8 which focuses upon the faunal and sediment differences between patches
and non-patches. Sampling methods, sample treatment, faunal sorting and
identification and statistical analyses for Chapter 8 were carried out in an identical
manner to those described here.
The experiment was repeated on the 18th August and the 18th December 1997 using
different P. elegans patch and non-patch plots in each experiment. The timings of the
3 experiments were aimed to coincide with high P. elegans larval availability (April),
moderate larval availability (August) and low availability (December)(see Chapter 3).
This was later confirmed by the abundances of P. elegans juveniles in Figure 6.2(ii).
The P. elegans individuals were divided into two groups a posteriori based on size.
Size measurements were carried out in an identical way to Chapter 3. The smallest
group ( 0.27mm, 5th setiger width) were considered to be 'juveniles' and those above
this size were considered to be 'adults'. These size definitions were determined from
the size distribution histograms (see results) - juveniles are those individuals which,
based on the size-frequency histograms, had settled from the plankton within the 3
week experimental period. All juvenile individuals sampled had already begun tube
construction at the time of sampling and, therefore, could be classed as settled larvae
as opposed to transients.
To determine whether there were any differences in the environmental variables of the
disturbed sediments between the two plot types, an additional experiment was carried
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