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Sediment water, organic and silt/clay contents - Figures 6.14 and 6.15 present the
results of the measured sediment variables in patch and non-patch azoic sediments 3
weeks after implantation. Figure 6.14 suggests that in December, there were no
statistical differences after 3 weeks implantation for water content, silt/clay fraction
and organic content between patch and non-patch azoics. Additionally, the organic
contents of the azoic sediments were similar to those of the ambient sediments (see
Figure 8.12(iii), Chapter 8) at this time. Therefore, it is likely that faunal responses
were not due to food accumulation in disturbed sediments as concluded in the study
by Thistle (1981).
The environmental conditions in the patch plots were not sufficiently different,
therefore, from non-patch plots to have any measurable effect on these sediment
parameters within 3 weeks. This suggests that faunal differences between patch and
non-patch azoic samples during December were not likely to have resulted from
differences in any of these three variables. Whether this holds true for the other
months cannot be assumed. Furthermore, the lack of a statistical difference for any
measured variable between plot type does not necessarily mean that the variable had
no effect on the invertebrate fauna since colonisation may be effected by subtle
differences in sediment conditions which were not detected. In addition, significant
changes in other sediment variables not measured in this experiment may have
occurred.
Redox potentials - In contrast to the bulk sediment granulometric characteristics, the
2cm and 4cm redox potentials of the treated sediments were significantly more
positive in patch sediments after 3 weeks compared to non-patch sediments. The
reason for this is not clear, especially since this was not the case for ambient
sediments at this time, (see Figure 8.13(iii), Chapter 8). However, it is unlikely that
differences in the redox potential at 2cm and 4cm sediment depths had any effect on
faunal colonisation since colonisation was almost exclusively via settlement and/or
migration onto the sediment surface (except perhaps for C. capitata).
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