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1986) and low level of replication resulting in too low a statistical power (Ragnarrson,
1996).
The present study was observational and not intended to determine the mechanisms
responsible for any differences in abundances between patch and non-patch
communities. However, the increased silt/clay fraction and higher meiofaunal
abundances in patches may have been due to increased passive deposition due to the
reduction in velocity of near-bed flow. In the same way, passive larval entrainment
may be responsible for some of the observed differences in this study. This was
observed even though tube-building spionids have been shown to ingest settling
bivalve larvae (Breese and Phibbs, 1972; Daro and Polk, 1973). Once an individual of
a species had colonised a P. elegans patch, the physico-chemical effects of the tubes
possibly concurred to provide an increased food supply in the form of the flourishing
microbial and meiofaunal communities observed in this study. Furthermore, the
resistance to shearing forces provided by the beds may have allowed a dense
community by virtue of individuals not being 'swept' away (Morgan, 1997).
Increased abundances of meiofauna (43%) were observed by Reise (1983b) in P.
elegans patches compared to areas lacking the spionid, whilst a similar increase has
been documented for beds of another spionid, Polydora ciliata, by Noji (1994), who
suggested that the meiofauna were utilising the worms faecal pellets as a food source.
The presence of C. volutator in patches, while almost completely absent outside
patches, probably resulted from active habitat selection of adults to areas of increased
silt/clay fraction and more stabilised sediments. This amphipod attains particularly
high densities in muddy sediments with high numbers of diatoms (Lawrie, 1996). Its
almost exclusive existence within patches suggests some sort of functional group
interaction (sensu Woodin, 1976) for this tube-building, deposit-feeding amphipod.
Similarly, Reise (1978) noticed C. volutator beds harbouring large numbers of P.
elegans in the Wadden Sea.
Sediment differences between P. elegans patches and non-patch areas.
Sediment analyses indicated that although sediment water content was the same for
patch and non-patch areas, the former consistently contained significantly increased
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