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A more detailed investigation of micro-scale spatial patterns of P. elegans was then
carried out. For this, cores were positioned linearly forming a transect rather than
forming an array as in the pilot survey. Although with this transect approach the
spatial distribution investigated was linear, and thus may have been influenced by the
direction of the line, it allowed a larger proportion of the P. elegans patch to be
sampled. Since each transect consisted of only 32 cores, 3 different patches could be
sampled each month. Sampling 3 patches each month overcame the linear bias of the
transect to a certain extent. The 3 patches were determined by random numbers each
month and the 32 cores forming a contiguous transect taken across them. Taking 3
replicate transects also limited the chance of any variability between P. elegans
patches being misinterpreted as temporal changes in micro-scale spatial patterns.
Thirty-two cores were chosen as a compromise between the practical work involved
and the number of samples needed to give enough sample pairs (i.e., 40, Sokal, 1986)
for reliable spatial autocorrelation analysis. Furthermore, 32 cores, i.e., 96cm,
encompassed most of the patch in one direction for the majority of patches.
The samples, which also provided the data on the population structure and
reproductive strategy of P. elegans (Chapter 3), were taken at the beginning of each
month from March 1997 until August 1997, and then every other month until
February 1998. After August 1997, it was decided that sampling alternate months
only was necessary since the main recruitment phase of the year had already occurred.
It was more important to sample as often as possible during the recruitment phase in
order to investigate adult-larval interactions.
The samples were treated and stored in the same way as described for the pilot survey.
These samples were washed over a 212).tm mesh sieve in addition to the 500iim mesh
sieve so that the numbers of newly settled individuals could be determined for each
sample. The samples were elutriated as described in Chapter 6 and the numbers of
'adults' (those with a 5th setiger width 0.30mm) and new recruits (those below a 5th
setiger width of 0.30mm), were counted. The size separation for new recruits was
determined from the size-frequency graphs in Chapter 3 (Figure 3.3(iii)) to distinguish
those individuals which had settled after the previous sampling occasion. Those
individuals above a 5th setiger width 0.30mm will be referred to as 'adults' for this
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