Download (20MB) - Repository@Napier

DISCUSSION
The main aims of this study were:
1) to investigate the spatial heterogeneity of the macrobenthic species and sediment
variables at different spatial scales on an intertidal sandflat;
2) to determine whether the heterogeneity created by a dominant biogenic species
affects the spatial patterns of other species.
The spatial patterns of macrobenthic species and sediments on Drum Sands,
Firth of Forth.
This study used a variety of techniques to assess the distributions of the macrobenthic
invertebrate species within the study area of Drum Sands. Firstly, a pilot survey was
carried out from which spatial heterogeneity was investigated using analysis of
variance. Although some species, e.g., P. elegans, C. edule and E. cf flava, had
significantly different mean abundances between plots at one or more scales, this
technique did not give a good insight into spatial patterns for several reasons. Firstly,
the survey was carried out during March when the invertebrate abundances were
generally low and secondly, although mean abundances of many taxa varied greatly at
different scales, most were non-significant because of large within-plot replicate
variability. This survey design is appropriate for pilot surveys giving an indication of
mean abundances and variability on an intertidal sandflat but gives little information
about their spatial patterns.
A much more detailed assessment of spatial patterns was given by the results of the
grid surveys using dispersion indices, mapping and spatial autocorrelation analysis.
Spatial patterns which were exhibited over scales of about 1-120m were defined in
these surveys. Patterns which occurred over the less than tens of centimetre scale
were lost in the small-scale heterogeneity and this was partly defined by the
constraints of the sampling design. At this scale, the spatial patterns of P. elegans
within high-density patches are discussed in Chapter 7.
Dispersion indices provided an assessment of the intensity of pattern but they gave no
information about the form of any pattern of macrobenthic invertebrates on Drum
Sands. Of the species sufficiently abundant for spatial analyses from the 1, 8 and 40m
51