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lack of apparent correlation must be treated with caution due to different sampling
regimes for the sediments and fauna. There were significant positive correlations of
P. elegans density with high levels of % organic content, % silt/clay, Md 4) and sorting
coefficient in the 8m and 40m surveys. Tube-building polychaetes have been shown
to affect these sediment properties (Noji, 1994; Morgan, 1997) and, therefore, the
sediments may not have been responsible for the generation of P. elegans patchiness
but vice versa. This will be discussed further for P. elegans on Drum Sands in
Chapter 8.
Drum Sands is a relatively high energy sandflat with frequent sediment movement
(pers. obs.) and macroalgal mats are capable of forming during the summer (summer
of 1996 for example). Therefore, the mosaic of species patches observed in this study
may have been generated by disturbances. The role of disturbance in structuring
macrobenthic populations on Drum Sands will be addressed in Chapters 4, 5 and 6.
This study revealed spatial patterns of many common intertidal macrobenthic species
found in European sandflats at various scales using regular grid-sampling techniques.
This sampling design is simple to carry out, is capable of covering a range of scales
and spatial patterns can be easily detected and displayed. This study revealed the
presence of patches of 1-2m2 in many species.
The effect of a dominant biogenic species on the spatial patterns of other
invertebrate species on an intertidal sandflat.
One of the most conspicuous biological features on an intertidal sandflat are the
mounds or plateaus formed by high densities of tube-building polychaetes. On Drum
Sands, P. elegans forms areas of smooth, raised sediment, approximately 1-1.5m2,
within an otherwise wave-rippled sandflat. These areas are characterised by increased
densities of P. elegans. Many studies have reported different sediment characteristics
within dense arrays of tube-building polychaetes (Dupont, 1975; Featherstone and
Risk, 1977; Noji, 1994; Morgan, 1997; Chapter 8) and these have resulted in different
faunal assemblages (Sanders et al., 1962; Fager, 1964; Ragnarsson, 1996; Chapter 8).
None of these studies, however, have assessed to what extent the spatial pattern
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