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METHODS
Survey design - It has been shown (see Chapter 2) that P. elegans forms patches of
increased density, approximately 1m2 in area, within the 400x250m study area on
Drum Sands. These patches could be seen as areas of smooth, raised sediment as
opposed to the wave-rippled sediments of non-patch areas. Eighty P. elegans patches
were marked by a cane, 2m away from the patch, and numbered. Some of these
numbered patches were used in later studies described in Chapters 6 and 8.
On each sampling date, 3 P. elegans patches were chosen at random for sampling.
Patches were sampled monthly between March and August 1997 and every other
month thereafter until February 1998. Thirty-two contiguous cores (3x3cm, 8cm
depth) forming a transect were taken across each patch. Preliminary sampling on
Drum Sands had shown that no individuals occurred lower than 8cm below the
sediment surface. These cores were also used to investigate micro-scale spatial
patterns of P. elegans (see Chapter 7). For the purpose of the present study the data
from the 32 cores were pooled. Therefore, an equivalent of 1 core (3x96cm) was
taken from three patches each month. The cores of sediment were then preserved in
10% saline formaldehyde solution, neutralised with Borax containing 0.01% Rose
Bengal stain. The samples were later sieved on 5001.tm and 212um mesh sieves. The
smaller mesh size retained newly settled P. elegans (Gudmundsson, pers. comm.).
The numbers of P. elegans and other fauna were counted, the former being kept in
70% alcohol for size and sex determination.
Size measurements and sex determination of P. elegans were carried out on only half
of each sample (i.e., 16 out of the 32 cores were randomly selected). This was a
necessary procedure due to the number of samples and the time involved in
determining the sizes of individuals. It was considered that this procedure would not
compromise the results obtained due to the large number of individuals. Size
determination of P. elegans individuals was carried out by measuring the width of the
5th setiger using a dissecting microscope (x40 magnification) fitted with an eyepiece
micrometer. Fifth setiger width measurements have been used as a standard body size
measurement technique for many spionid polychaetes (e.g., Yokoyama, 1990; Zajac,
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