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METHODS
Survey design - During late August 1997 mats of green algae (Vaucheria subsimplex)
developed within the study site in approximately the same area as the previous
summer (see Figures 4.1 and 5.1). The general appearance of the mats (1-2m 2) closely
resembled those which occurred the previous year, except for the absence of E.
prolifera. The V. subsimplex mats covered approximately 30-35% of the sediments
within the area affected by weed and approximately 100% within mats. This allowed
an ideal opportunity to study the effects of natural macroalgal mats on the sediments
and their invertebrate faunal assemblages. The inherent disadvantage of such a
descriptive study, i.e., the large-scale spatial separation of weed-affected and weed-
free areas, was overcome in this study since weed-free areas remained within the
weed-affected area in which non-weed plots could be positioned. Therefore, any
large-scale factors affecting the fauna within the study area, independent of the effects
of weed cover, should have acted on both the weed and non-weed plots.
On the 18th September 1997 (approximately 4 weeks after V. subsimplex first
established), 6 'weed' plots and 6 'non-weed' plots, 1m2 each, were randomly located
within a selected area (50x50m) of the sediments affected by macroalgal cover. This
was achieved by choosing the nearest weed mat and weed-free area to the randomly
generated co-ordinates for the weed and non-weed plots respectively. The layout of
the two plot types are shown in Figure 5.1. The assumption that the weed had no
effect on the characteristics of the non-weed areas was made. This assumption
seemed reasonable with respect to hydrodynamic effects at least since the V.
subsimplex possessed very short filaments and, therefore, had a very localised
hydrodynamic effect.
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