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DISCUSSION
This study specifically addressed 2 questions, these were:
(1) what is the micro-scale spatial distribution of dense populations of tube-building
spionids and what does it suggest about intraspecific interactions?;
(2) what are the roles of larval recruitment, interspecific interactions and abiotic
variables in determining spatial patterns?
These questions were addressed using P. elegans as an example.
The micro-scale spatial patterns of P. elegans within high density patches on
Drum Sands.
Linear transects of 32 contiguous cores were taken monthly from 3 small-scale P.
elegans patches from March to August 1997, and then every other month until
February 1998. Dispersion indices suggested that all through the sampling period
(except October 1997) the distribution of adult P. elegans individuals showed a
significant departure from random (in at least 2 of the 3 replicates), all of these were
aggregated distributions, i.e., their variances were significantly greater than their
means. There was generally a very good agreement between the 3 dispersion indices
used (I, Id and Ii.,) which suggests that confident statements can be made about these
results (Myers, 1978).
The form of these patterns were investigated using mapping (nearest-neighbour
gridding technique) and spatial autocorrelation analysis. Spatial autocorrelation
analysis allowed the nature of patterns and estimates of patch sizes to be made. In
general, these patches of increased adult P. elegans densities were smaller than the
sampling units (i.e.,