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Geographical variation
Speaking next of the large, continuous nature of the CCFZ habitat,
Smith observed that, while many people thought of the deep sea as
relatively uniform, there were gradients, both longitudinally and latitudinally.
One way to observe such gradients was to look at the abundance of animals
on the seafloor. As noted above, the abundance of animals was generally
correlated with POC flux in the deep sea, so that macrofaunal abundance in
particular could be used to say something about the POC flux regime.
Looking at data on animal abundance at a number of stations in the
CCFZ, moving from Echo 1 in the east to DOMES A in the west, he noted a
change by roughly a factor of four in regard to macrofauna: 64 animals per
square metre in the west and up to 260 animals in the east. This implied
differences in a variety of environmental characteristics, particularly POC
flux to the seafloor. Moving to the EqPac station at 9° N in the eastern
CCFZ also showed a four- to fivefold change in abundance. In addition to
those longitudinal changes, moving just four degrees from north to south
into the zone influenced by equatorial upwelling demonstrated a sixfold
change in abundance from EqPac 9° N to EqPac 5° N. So there clearly
were gradients in the abundance of animals as one moved through the
CCFZ, and presumably also in a number of environmentally important
factors such as POC flux. Other evidence showed that there was not just
one continuous fauna from one end of the CCFZ to the other.
High species diversity
Smith next cited data on overlaps in species lists of polychaete
fauna at various Domes A and Echo 1 sites, showing that from 5-15 percent
of the species at each site were not found at other CCFZ sites. If the fauna
were identical and broadly distributed throughout the zone, one could argue
that mining in different areas would not cause species extinction, as long as
there were some preservation reference areas in other parts of the zone.
Nevertheless, levels of atomicity -- the amount of species turnover as one
moved from one end of the zone to the other -- were highly controversial
and difficult to assess. These areas had been poorly sampled: Domes A
was represented by about 47 box-core samples and Echo 1 by something
like 2 box cores. Thus, one could argue that some species were simply rare
and that sufficient sampling would eventually generate the same species
lists at different sites. Such an argument might be valid until more detailed
or more exhaustive research had been conducted in the nodule province.
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