standardization of environmental data and information - International ...

One potential impact of discharging into the near-surface water a
large amount of deepwater heavily loaded with nutrient might be to shift the
ecosystem more toward the classic food chain. One might ask if that was
such a bad thing. However, whether good or bad, changing the functioning
of a large ecosystem was obviously something that warranted caution.
Looking at how the phytoplankton functioned in the epipelagic
ecosystem, he recalled that the Japanese and Korean investor groups, in
presenting their data to the Workshop (chapters 8 and 10 above), had
described the typical profile of low chlorophyll in the near-surface waters
and a chlorophyll maximum at about 75-125 m. This was typical of open
ocean systems, where the near-surface layers, above 50 m, had high light
but low nutrient levels and very low chlorophyll. The phytoplankton in that
region might be working by nitrogen fixation or they might simply be
predominantly very small cells, whereas down in the chlorophyll maximum
the low light conditions were at the boundary where nutrient was high. As
Sibuet had mentioned in regard to bacteria (chapter 9 above), one could
not directly relate chlorophyll, whether high or low, to productivity. Perhaps
the cells in the upper water were turning over quickly while the others were
turning over slowly. In any case, it was vital to sample the two regions to
see both community composition and productivity.
As for zooplankton, one of the key issues was which group,
microzooplankton or macrozooplankton, were the dominant herbivores at
this level of the food chain. Standard dilution experiments to measure
microzooplankton grazing, like those reported by the Korean research group
(chapter 10 above, section 3.3.2), might be incorporated into the impact
assessment to measure the relative importance of the two groups.
An important feature of the macrozooplankton was that many of
them carried out diel vertical migrations down to 100-200 m, which was
important in designing the sampling. With a single oblique haul from 200 m
to the surface, for example, there was no way to know where the plankton
were in the water column, the near-surface layer or down in the chlorophyll
maximum. It might be important to carry out sampling both day and night,
and to conduct depth-stratified sampling, in order to tell where the
zooplankton were in the water column.
Among the fish groups were a combination of epipelagic
planktivores and mesopelagic migrating planktivores such as mictophids.
There were a number of deep-water planktivores, of which the mictophids
were probably the best known. These groups migrated down to several
408
INTERNATIONAL SEABED AUTHORITY