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oughness elements (Nowell and Church, 1979; Nowell et al., 1981) and/or the
indirect effect of increased microbial sediment-binding (Eckman et al., 1981). The
altered physical, chemical, physico-chemical and biological conditions encountered
within these tube-beds have been shown to result in different infaunal macrobenthic
(Sanders et al., 1962; Fager, 1964; Ragnarsson, 1996) and meiobenthic (Reise, 1985;
Noji, 1994) communities compared with non-patch areas.
The processes responsible for the formation and maintenance of such patches, in
contrast to micro-scale patches, have not been explicitly studied. Relating observed
patterns to the underlying processes which help to create them is difficult, even at the
tractable scale at which manipulative experiments can be conducted (Hall et al.,
1993). However, several authors have proposed that sediment disturbance and the
appropriate life history characteristics for their particular environment are
prerequisites for patch formation. Carey (1987) suggested that there was an
association between L. conchilega, macroalgal mat establishment and intermittently
high sedimentation rates for L. conchilega mound development on St. Andrews Bay,
Scotland. Fager (1964), however, suggested that a period of calm conditions after
larval settlement could have led to the formation of the 0. fusiformis patches. Morgan
(1997) postulated that in view of the reproductive strategy possessed by the P. elegans
population in the Baie de Somme, France, gregarious larval settlement and increased
adult immigration into, or lower adult emmigration and/or lower mortality within
patches, were important prerequisites for the formation of tube-beds. Many spionid
polychaetes are capable of reaching very high numbers following a disturbance and
have been described as opportunists (Grassle and Grassle, 1974; Pearson and
Rosenberg, 1978). How this relates to formation of the observed patches is not clear.
However, it would appear that for spionid tube-bed formation, some sediment
disturbance is likely to be an important prerequisite.
THE PRESENT STUDY
On Drum Sands, Firth of Forth, Scotland, the tube-building, spionid polychaete
Pygospio elegans forms small-scale patches which can be seen as areas of smooth,
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