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DISCUSSION
The aim of this study was specifically to investigate the population structure and
reproductive biology of P. elegans on Drum Sands, Firth of Forth, and to elucidate the
significance of these factors for population maintenance and the generation of the
spatial patterns exhibited by P. elegans on this sandflat.
Population structure and reproduction of Pygospio elegans at Drum Sands.
This study has indicated that P. elegans on Drum Sands has adopted a planktonic
mode of reproduction. No evidence of asexual reproduction and/or the production of
benthic larvae was found between March 1997 and February 1998 for this population.
At peak periods of larval development, approximately 50% of the adult female tubes
contained embryos and/or larvae during the spring of 1997, although the following
year, during February 1998, this reached 80% of the adult female population. Larvae
were released at the 3-5 setiger stage into the water column. Settlement occurred
during two main recruitment phases: the first, and numerically the most significant
occurred during April/May 1997 while the second occurred during
November/December 1997. Larvae settled at a size of approximately 0.13-0.17mm
5th setiger width, or 20 setigers, and grew rapidly (around 23 setigers/month) reaching
sexual maturation size within 3 months after settlement. The adult population always
consisted of a greater proportion of females than males, especially during the summer
when the female:male ratio reached 6.19±0.48. Sampling was carried out from high
density patches only and it is assumed that the same reproductive strategy and
population structure occurred in lower density areas, although sampling in these areas
would have been necessary to confirm this.
Since P. elegans has been shown to exhibit very different reproductive strategies in
different localities, it is not possible to predict the reproductive biology of a particular
population. This point was addressed by Levin (1984b) who stated 'we should not
assume that life history traits reported in the literature for a particular population will
necessarily be accurate for different populations'. Consequently, assessing the timing
and method of reproduction and the mode of larval development were prerequisites
for the study of the processes affecting the spatial distribution of the P. elegans
population at Drum Sands.
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