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Micro-scale spatial patterns of macrobenthic invertebrates, like those observed at
larger scales, have mainly been found to be aggregated. For example, Zettler and Bick
(1996) found Marenzelleria viridis formed patches down to 0.04m 2 and proposed that
these could have been created by sediment structures, substrate preferences, feeding
mode and biotic or abiotic attractants. Eckman (1979) combined small-scale
manipulative experiments with direct observations and showed that polychaete spatial
patterns were affected by the locally varying hydrodynamic environment at the
centimetre scale. He suggested that the lcm patches formed by Tanais sp. and
Manayunkia aestuarina in his experiment resulted from the presence of simulated
animal tubes, and that the 10cm periodicities in the abundances of many other species
in Skagit Bay, Washington, resulted from the hydrodynamic patterns created by bed
ripples. Reise (1979) suggested that the micro-scale patches formed by all 5 species in
his study on the intertidal sandflats of the island of Sylt, North Sea, could be related to
their feeding modes.
Uniform distributions at this scale are generally ascribed to some type of negative
interaction between individuals. Connell (1963) directly observed the development of
spatial patterns of the marine amphipod Ericthonius brasiliensis. He found that the
uniform distributions shown by this species resulted from territorial behaviour by the
adults. Similarly, Levin (1981) found, using nearest-neighbour analysis, that
Pseudopolydora cf. paucibranchiata was uniformly distributed while Streblospio
benedicti was random. She showed that P. cf. paucibranchiata's distribution was
initiated during larval settlement and enhanced by subsequent interactions (palp-
fighting) between post-larval individuals.
In Chapter 2, the small- and meso-scale (m-100m) spatial patterns exhibited by
macrobenthic invertebrate species on an intertidal sandflat were investigated. The
spionid polychaete P. elegans formed patches, 1-1.5m 2, of increased density
characterised by smooth, raised sediments. Since there is a limit to the range of scales
of heterogeneity investigated by any one survey, the micro-scale spatial patterning of
P. elegans could not be investigated. Spatial patterns that reflect micro-scale
interactions, processes and responses smaller than the sampling unit (25cm) were
therefore homogenised.
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