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Other theories have been postulated for the observed community differences within
tube-beds. Woodin (1978, 1981) suggested that the observed effects result from the
'refuge' provided by the high numbers of tubes. Both predation and local
disturbances have been shown to be important structuring forces for soft-bottom
infauna (Reise, 1978; Woodin, 1978; Zajac and Whitlatch, 1982a; Ambrose, 1984;
Thrush, 1988; Hall et al., 1993) and Woodin (1978) suggested that refuges may be
created by organisms whose structures buffer the impact of physiological stress or
inhibit the access of predators. Woodin (1976) viewed soft-bottom community
structuring from the perspective of 'functional group' interactions in which 'tube-
dweller', `bioturbator' and `suspension-feeder' functional groups should each be
unfavourable to each other. This 'functional group' interaction hypothesis implied
that the maintenance of discrete dense assemblages in infaunal systems was due to
interactions between established infaunal individuals and settling larvae. Therefore, a
tube-building species would be expected to exhibit increased densities within an
assemblage of other tube-builders by this interaction, whilst bioturbators and
suspension-feeders would be expected to exhibit lower densities.
The main tube-building polychaete species forming dense tube-beds in northern
European shallow waters tend to be either Lanice conchilega or Pygospio elegans.
Several studies such as Eagle (1973, 1975), Carey (1982) and Ragnarsson (1996) have
described the fauna within L. conchilega tube-beds, however, relatively few studies
have focused on the beds formed by P. elegans (e.g., Dupont, 1975; Morgan, 1997).
The dense tube-beds at Drum Sands allowed an investigation of the effects of this
tube-builder on an intertidal sandflat. Specifically, the differences in the biology and
the sediments within P. elegans patches and non-patch areas of sand were studied.
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