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CHAPTER 7
THE MICRO-SCALE SPATIAL PATTERNS OF PYGOSPIO
ELEGANS WITHIN SMALL-SCALE PATCHES AND THE ROLES
OF INTRA- AND INTERSPECIFIC INTERACTIONS AND ABIOTIC
INTRODUCTION
EFFECTS
Several studies have reported the presence of spatial aggregations of marine benthic
invertebrates at the centimetre (micro-) scale although their sampling regimes were
inappropriate to have investigated them fully. For example, Angel and Angel (1967)
found clustering of 3 infaunal species at Fanafjorden, Norway, at the scale of their
smallest sample size (12.5cm) and reasoned that their core size may have been too
large to detect the minimum sizes of the patterns. Similarly, Gage and Coghill (1977)
using linear transects of 5cm contiguous cores found clustering at the scale of the
sampling unit or smaller for several infaunal species at 2 Scottish sea lochs.
Consequently, later studies investigating the presence and importance of micro-scale
spatial heterogeneity of macrobenthic individuals have used smaller contiguous cores
or nearest-neighbour techniques and the information obtained from such studies has
led to both a greater understanding of both how these populations are regulated and an
increased appreciation of the importance of biotic interactions (Eckman, 1979; Reise,
1979; Levin, 1981; Lawrie, 1996; Zettler and Bick, 1996). In general, processes
operating at the micro-scale, which tend to act upon the individual rather than the
population, can be classed into two broad categories. Processes such as habitat
heterogeneity, symbiosis, gregarious behaviour and/or limited dispersal of progeny
tend to produce aggregated distributions while negative interactions such as
territoriality, avoidance behaviour and/or allelopathy often create uniform
distributions (Levin, 1981).
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