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DISCOL provided a few observations on the slow development of the
faunal stock. Seven years after the experimental impact, community
structure was still disturbed, as shown mainly by the irregular distribution of
species and the differences in diversity patterns (figure 7), e.g. for
polychaetes 24 . The megafauna has not re-established its original densities
after this interval (figure 6).
Fig. 6 Megafauna abundance change during DISCOL/ATESEPP 25 .
When evaluating the effects of deep-sea mining the larger areas to
be impacted and the higher impact intensity need to be considered. The
topography of the seafloor, with its strong depth gradients and steep
escarpments, is unsuitable for mining, and the heavy equipment will not
touch areas with low nodule densities. Qualified plot sizes fall in the range
of 20-100 km²; the direct mining influences, however, will reach beyond
these limits. Regions of similar or even larger size will remain between the
mining plots, probably unimpacted except for resedimentation from the
mining plume. They should serve as sources for the immigration of adult
specimens and for the production of larvae.
It is correct to assume that recolonisation of species takes place
over (long) periods and that the reestablishment of a balanced community
will occur. This community, however, will be differently structured from the
one existing before the nodules were mined. The epifauna has no chance
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