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productivity and could profoundly alter community composition, and species
and size structure. Speaking facetiously, Koslow said that if discharges
visible from satellites took place totally into the surface water, they might
impact the global carbon budget, enabling the mining companies to obtain
carbon credits. Recent iron-enrichment experiments in the equatorial
current in the South Pacific had shown that a single enrichment in surface
water had had a measurable impact on both production and species
composition. Therefore, in a chronic, long-term operation continually
pumping deepwater up to the surface could have a substantial impact.
Other possible impacts might result from the release of trace metals
into the euphotic zone. It was unclear whether the effects would be positive
or negative. Some trace metals such as iron had been shown to be limiting;
since the nitrogen fixation taking place in surface waters had a strong need
for iron, trace metals would enhance that kind of productivity. They might
also have a negative impact by poisoning some cells, thereby altering
community composition.
The release of particulates such as sediments or tailings into the
euphotic zone would affect light penetration and decrease the depth of the
zone, which would presumably have a large impact on the deep chlorophyll
maximum at the base of the zone. For zooplankton, the release of
particulates would presumably reduce the feeding efficiency of suspension
feeders. Enhanced or decreased productivity at lower trophic levels would
enhance or decrease secondary production. Any change in the size
structure and species composition of the phytoplankton would presumably
affect the zooplankton. Again, there was the potentially toxic effect of
sediment plumes and trace metals.
Moving on to the micronekton and nekton, he said flow-on effects
would again result from changes in primary and secondary productivity, size
and frequency distribution. There might also be bioaccumulation of toxins,
probably not a trivial issue since a number of commercial species, such as
tuna and swordfish, already had fairly high levels of heavy metals in their
tissue naturally and one would not want to increase them. As to potential
impacts on larval fish, there might well be a number of tunas in both the
Indian Ocean area and in the Pacific, since several tuna species typically
spawned in the open ocean.
Speaking finally of seabirds, he mentioned a dumping site off
Tasmania where jarosite, a waste product of zinc mining, was being
dumped and where testing of a small seabird had raised concern about
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