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samples from each of the three deposition areas selected on the basis of
sediment-trap and current-meter results, and according to distance from
the tow tracks. However, sufficiently precise sampler positioning was not
possible; therefore, the sampling strategy was modified to the "line-transect
method" (25, 50 and 100 m distance from the tow tracks). By means of
several approaches of impact evaluation (see section 3.4 below), the
environmental decline was identified in JET 3 and 4, so that it was
necessary to consider another sampling strategy. The sediment samples in
JET 3 and 4 were collected at random from areas broadly categorised as
heavy deposition areas, medium deposition areas, light deposition areas
and no deposition (reference area), respectively.
Fauna JET2 JET3 JET4 References
Sedimentary
bacteria
ns # # 10
Meiobenthos significant significant ns 11
Macrobenthos nd Nd (significant) 12
Megabenthos nd Nd significant 13
ns = the difference was not statistically significant; significant = significant
difference was observed; (significant) = significant differences were observed in
some of the taxonomic groups; nd = no data; # = statistical approach was not done.
Table 3
Comparisons of faunal abundance between natural and postdisturbance
conditions.
In general, the abundance of megabenthos is so low that it is almost
impossible to survey with the sediment sampler 14 . In the case of JET, a
video-observation system (hereafter referred to as FDC: Finder-installed
Deep-Sea Camera) was used. During the observation, to maintain a 3-m
width of coverage area, the assembly was towed with the object of keeping
a constant distance of about 3 m above the sea bottom.
The observations were conducted along the line transects where the
area was divided into deposition and no deposition areas. For quantitative
output of the megabenthos study, it was necessary to observe several
hectares, so that five transect lines were established in JET 4 (Figure 10).
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