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RESULTS The species abundances in each core for this survey are given in Appendix 2. This appendix gives the numbers of adult P. elegans per core for each replicate, together with the numbers of P. elegans tubes containing embryos or larvae, the numbers of P. elegans new recruits and the numbers of other species. After P. elegans, species are listed in the order according to Howson and Picton (1997). This data is also used in the investigation of the micro-scale patterns of P. elegans in Chapter 7. Size distribution of Pygospio elegans - The use of 500pm and 212m sieves throughout the study allowed a more accurate assessment of the population size structure of P. elegans than would be obtained by the use of a 500pm sieve alone (Gudmundsson, 1985; Yokoyama, 1990; Morgan, 1997). The use of the smaller mesh size allowed the assessment of the numbers of new recruits as near as possible (given the monthly sampling regime) to their time of settlement rather than after a period of growth. This allowed the timing of settlement to be more accurately determined and gave a more realistic population size distribution (Bachelet, 1990). However, a small error might have arisen in this study due to the relatively long time intervals between sampling intervals. Livingston (1987) provided direct evidence that monthly sampling might obscure the weekly variations in recruitment. Regression analysis of 1398 P. elegans (36.47% of the total sample) indicated that there was a highly significant regression between the width of the 5th setiger and the body length of P. elegans (p
growth (Yokoyama, 1990) suggesting that the variability may have been partly caused by individuals undergoing sexual reproduction. Total setiger number, suggested by Anger et al. (1986) to be a better guide to body size for spionids, can be estimated using the equation given by Morgan (1997); I • 1 • E 0.80 • •S toc 0 0.60 o ba o — 0.40 1.40 y= 1.69x+ 1.56 1.20 r: O.854 0.854 1.00—* 0.20 0.00 Total setiger number = 9.85 + (93.6 x 5th setiger width (mm)) (Equation 2) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • * • • • • -0.90 -0.80 -0.70 -0.60 -0.50 -0.40 -0.30 -0.20 -0.10 0.00 logm width (mm) Figure 3.1 : Regression line of 5th setiger width against length for P. elegans, n=1398. The smallest post-planktonic individuals found had 5th setiger widths of 0.13mm (or 22 setigers according to Equation 2 and 18-22 setigers by direct counting of a sample of these individuals, n=25). This agrees with the findings of Hempel (1957) and Rasmussen (1973) who suggested that P. elegans may settle from the plankton anywhere between 11-20 setigers. This study suggested that adult P. elegans sexually mature when they reach a 5th setiger width of approximately 0.37mm. This corresponded to the smallest size that branchiae were found on the 2nd setiger of P. elegans throughout the sampling period. Since this method only determined the size at which males mature, the assumption made here is that both males and females mature at the same size. This size 66
- Page 30 and 31: variance (TTLQV) techniques (see Lu
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- Page 34 and 35: Holme and McIntyre (1984). Percenta
- Page 36 and 37: Pattern Analysis - Grid Surveys Sur
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- Page 66 and 67: DISCUSSION The main aims of this st
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- Page 90 and 91: Pygospio elegans showed great seaso
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RESULTS<br />
The species abundances in each core for this survey are given in Appendix 2. This<br />
appendix gives the numbers of adult P. elegans per core for each replicate, together<br />
with the numbers of P. elegans tubes containing embryos or larvae, the numbers of P.<br />
elegans new recruits and the numbers of other species. After P. elegans, species are<br />
listed in the order according to Howson and Picton (1997). This data is also used in<br />
the investigation of the micro-scale patterns of P. elegans in Chapter 7.<br />
Size distribution of Pygospio elegans - The use of 500pm and 212m sieves<br />
throughout the study allowed a more accurate assessment of the population size<br />
structure of P. elegans than would be obtained by the use of a 500pm sieve alone<br />
(Gudmundsson, 1985; Yokoyama, 1990; Morgan, 1997). The use of the smaller mesh<br />
size allowed the assessment of the numbers of new recruits as near as possible (given<br />
the monthly sampling regime) to their time of settlement rather than after a period of<br />
growth. This allowed the timing of settlement to be more accurately determined and<br />
gave a more realistic population size distribution (Bachelet, 1990). However, a small<br />
error might have arisen in this study due to the relatively long time intervals between<br />
sampling intervals. Livingston (1987) provided direct evidence that monthly<br />
sampling might obscure the weekly variations in recruitment.<br />
Regression analysis of 1398 P. elegans (36.47% of the total sample) indicated that<br />
there was a highly significant regression between the width of the 5th setiger and the<br />
body length of P. elegans (p
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