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Chapter 17
Pelagic Community Impacts and their
Assessment
Dr. J. Anthony Koslow, Research Scientist, CSIRO Marine
Research, Commonwealth Scientific and Industrial Research
Organization , Hobart, Tasmania, Australia
The mining of polymetallic nodules on the high seas has the
potential to impact vast areas, both on the seafloor and in the water
column. Potentially exploitable deposits of polymetallic nodules are found
over large expanses of the abyssal Pacific and Indian Oceans 1 . A key area
of commercial interest, the Clarion-Clipperton Fracture Zone (CCFZ), is
situated in the North Pacific Ocean between Mexico and Hawaii, in a region
that appears to lie between the highly oligotrophic North Pacific tropical gyre
and the more productive North Pacific Equatorial Countercurrent / eastern
tropical Pacific regions 2 . The plankton in this region, particularly of the
tropical gyre, is characterized as having high diversity and stability and
being remote from terrestrial influences 3 . Weak seasonality is observed in
both regions. Interannual variability may be as great or greater than
seasonal variability, as seen from the Hawaii Ocean Time-series (HOT)
investigations 4 . Seasonality in the two regions differs: higher productivity is
observed in winter in the central gyre but in spring and autumn in the
countercurrent region 5 . The zooplankton communities are considered
“climax” communities, based on the considerable age of these mid-ocean
ecosystems, their stability and lack of disturbance. There is little basis on
which to project the likely impact of mining operations.
Deep-sea nodule mining may be anticipated to transport
considerable sediment and deep water to the surface mining vessel: an
estimated 7,400 tons of sediment and 34,560 cubic metres of water per
day 6 . If discharged at the surface, this would likely have a substantial
impact on the pelagic ecosystem, based on the flux of nutrient into
oligotrophic water and the influence of sediment on light penetration, tracemetal
concentrations and the feeding of planktonic suspension feeders 7 . It
was therefore agreed at the 1998 Workshop of the International Seabed
Authority in Sanya, China, on environmental guidelines for deep-seabed
polymetallic exploration, that discharge should be below 200 m, the
approximate depth of the epipelagic zone, and if possible, deeper than
1000 m, below the oxygen-minimum zone and the depth of vertical
migration for much of the fauna within the upper pelagic zone 8 . I assume in
this paper that this deep-discharge recommendation will be followed to
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INTERNATIONAL SEABED AUTHORITY