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distribution at the micro-scale. Adult-larval interactions and sediment heterogeneity
were implicated as being important processes in determining P. elegans distribution at
this scale. However, inferring processes based on spatial co-occurrence is very
ambiguous and controlled laboratory and/or field investigations would be required to
support these predictions.
Trying to match observed patterns to particular processes is inherently difficult
(Hewitt et al., 1996). Heterogeneity results from a complex interaction of biotic and
abiotic processes (Livingston, 1987; Caswell and Cohen, 1991) and, intuitively, it is
likely that a given pattern may result from a combination of processes. The practical
and conceptual difficulties associated with such an investigation were emphasised in
this study. The small-scale patterns of P. elegans on Drum Sands were relatively
distinct and were present at the tractable scale of experimental investigations. Factors
previously proposed as being responsible for spionid patch formation were shown to
lead to localised increases in P. elegans numbers, and, therefore, the second aim of
this thesis was successfully achieved. However, the role of these processes in patch
generation was not unequivocally shown. Consequently, further research should be
carried out, including a more detailed investigation into the macroalgal mat
establishment on Drum Sands (weed type, biomass and timing), a study of the
localised hydrodynamics on Drum Sands and further studies on larval settlement of P.
elegans (their responses to the presence of adult conspecifics, boundary flow and
sediment heterogeneity).
The ecological importance of small-scale P. elegans patches on Drum Sands.
The final part of this study showed that P. elegans patches were discrete ecological
habitats. It must be remembered that associating the changes in numbers of a species
to changes in the structure of associated communities in the field is inherently dubious
due to the inability to control environmental variables. Consequently, the use of
controlled, manipulated experiments are advocated.
Within the P. elegans patches on Drum Sands, many invertebrate species, e.g., C.
capitata, C. edule, M. balthica and C. volutator, exhibited significantly increased
abundances compared to non-patch areas, and the population size structure of some
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