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The sediments could not be sampled prior to macroalgal mat development since weed
mats had to establish before the two plot types could be positioned. Therefore, the
assumption is made that the faunal and sedimentary characteristics in the weed plots
were initially similar to the non-weed plots, i.e., that algal mat establishment within
the area was random. This assumption seemed reasonable with respect to P. elegans
densities since the macroalgal mats were not restricted to P. elegans patches.
Furthermore, the weed and non-weed plots were not placed at any of the previously
marked P. elegans patches. However, the patchy nature of weed mats suggested that
their establishment was probably influenced by some unidentified factor and,
therefore, initial conditions within the two plot types may not have been identical.
On 18th September 1997, these plots were sampled for their invertebrate fauna using
an identical method to the one described for the controlled, weed-implantation
experiment (see Chapter 4). These will be referred to as '4 weeks' samples hereafter
since these samples were taken 4 weeks after algal establishment. The sediments were
sampled and redox potentials measured in an identical way as described in Chapter 4.
Redox measurements were also taken on the 16th of October, i.e., 8 weeks after V.
subsimplex establishment. Redox profiles were taken at 3 depths only; 1, 2 and 4cm,
since the results from the weed-implantation experiment suggested that deeper
measurements only showed the same trends as near-surface measurements and were
less ecologically significant to the species studied. Sample treatment thereafter was
the same as described in Chapter 4.
Sampling was repeated on the 8th of January, 1998, 20 weeks after algal
establishment. The weed had been slowly disappearing since mid November and by
this time had almost completely disappeared.
One random sample (6x6cm) was taken from each plot for weed biomass
determination after 4 weeks and 20 weeks and treated in the same way as described in
Chapter 4.
Fifth setiger widths were measured of all P. elegans individuals from both the weed
and non-weed plots for both the 4 and 20 weeks samples as described in Chapter 3.
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