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availability for patch foundation. No evidence for the production of benthic larvae
and/or asexual proliferation was found. It is conceivable that the latter two methods
of propagation could lead to patch formation since they are likely to produce localised
areas of increased density. A planktonic mode of development, however, made P.
elegans more suited to respond to large-scale disturbances (Levin, 1984a). The
reliance on planktonic larval development for population maintenance suggested that
several conditions must have occurred on Drum Sands for the generation of the small-
scale patches of increased density present within this area. Firstly, patches must have
initially been areas of increased larval recruitment. Macroalgal mat development
and/or sediment disturbance are two factors which could have led to these high
juvenile numbers. These were investigated in Chapter 4, 5 and 6. Since recruitment
of this P. elegans population was very seasonal, the timing of these perturbations must
coincide with a recruitment phase. Secondly, there must be increased adult and/or
larval recruitment to these patches for patch maintenance. Although other factors may
have initially been involved, such as localised areas of increased larval deposition due
to eddy currents, these were not addressed in the present study.
The possibility that the establishment of macroalgal mats may have been responsible
for the generation of increased numbers of P. elegans was firstly investigated in
Chapter 4 by a controlled weed-implantation experiment. This study showed that E.
prolifera, at a relatively low biomass compared to other experimental studies, had a
negative effect on P. elegans numbers, both on adults and larval recruitment. The
communities underneath E. prolifera mats became numerically dominated by C.
capitata. These results suggested that E. prolifera mats may not have generated P.
elegans patches. However, the possibility that P. elegans increased in numbers as a
later successional species in areas dominated by C. cap itata after E. prolifera decay
could not be investigated due to mussel settlement on experimental plots.
Although controlled, experimental investigations into the ecological effects of
macroalgal mats are potentially less equivocal than comparative surveys, their results
tend to be less specific to a particular environment. This is because macroalgal
manipulation experiments are likely to show different effects from surveys focusing
upon mats which develop naturally unless all aspects of the implanted weed closely
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