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Blanketing of sediment, nodules and fauna occurred in large areas,
however, presumably in sub-lethal thickness. During post-impact studies,
those effects were not adequately recorded. The benthic impact
experiments (BIEs) of the United States, Japan (Japan Deep-Sea Impact
Experiment [JET]), the Interoceanmetal Joint Organization (IOM) and India
(Indian Deep-sea Environment Experiment [INDEX]) have so far not supplied
suitable answers. It is not clear whether blanketing generally or a specific
thickness of resedimentation results in the death of animals.
When attempting to make general statements on the effects of
mining it is also important to remember that the total area experimentally
impacted and the impact density within the area have not reached the
extent expected in commercial mining. It also remains impossible to predict
either the extent of impact when single mining units are combined into
areas of up to 100 km² or the length of time benthic communities will
require to regain their balance.
2.2. Effects
The fauna of the deep seafloor inhabits strata that will be the most
impacted by nodule uptake. Most of the animals live on or in the semiliquid
layer or constitute the epifauna of the nodule surfaces protruding
from the sediment into the water. This component of the fauna will be
totally exported and destroyed unless at least a few nodules remain in
place. Techniques for steering the miner, however, are so far advanced
that almost the total area will be cleared. Should small plots remain
unmined between the miner tracks, sediment may be shifted over them or
they will probably be blanketed during the follow-up passes by the miner.
The fauna inhabiting the hard substrate are likely to be destroyed. Most of
the epifauna is bound to the nodule surface. Higher taxa found exclusively
on nodules are the Bryozoa and the Brachiopoda. Other taxa having many
species that rely on the nodules are the Xenophyophoria, Porifera,
Polychaeta and Nematoda. For these species the environmental alteration
caused by mining is irreversible in terms of human time scales, because
nodule growth takes place over the span of a million years for a few
millimetres of precipitation.
Whereas some demersal fish species, shrimps and swimming
holothurians may be able to escape the miner system, towed at about 1
m/second, all other sediment-living fauna will be subjected to the mining
process along with the nodules and the sediment. Faunal components
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