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France, but its research was oriented toward the Mediterranean Sea. She
hoped more work would be done on the water column just above the
bottom. Nothing was known about near-bottom plankton and larvae, due to
the lack of good devices for that environment. She thought this could be
achieved in an international framework, as it would be interesting to see
whether the functioning and structure of these communities differed from
one exploration area to another.
Referring to data on temporal variations at a single site, a
participant asked how the researchers made sure that they were
investigating exactly the same site each time. Sibuet replied that the study
had relied on replicates -- for example, six to eight box cores each time at
nearly the same place. The place could not be exactly the same, but the
researchers tried to do their best and believed that their statistics were
correct enough.
The same questioner asked whether there had been an accurate
analysis of the sediments from which biotic samples had been taken, to
ensure that they came from the same type of surroundings. Sibuet
responded that, for the physicochemical characteristics of deep-sea
sediment, granulometry had been used along with chemical analysis of
such ever-present parameters as organic carbon and nitrogen. The
granulometry showed no significant change, with the sediment remaining a
smooth mud. Organic carbon was a bad indicator that did not change
enough. The best parameter was carbon flux, whose variations were not
confined to the sediment layer.
Some samples had displayed a temporal change in lipids -- not in
terms of total amounts but in reference to a special lipid, which had been
buried. These changes were difficult to analyse without detailed research
into biology and chemistry.
Asked to elaborate on her data showing a seasonal cycle in the
density of polychaetes, Sibuet said that samples from a tropical
environment showed minimal seasonal variation in the flux of particles,
whereas a strong seasonal change occurred at a temperate station in the
northeast Atlantic Ocean. For the benthic community, however, it was
difficult to measure response to seasonal changes in particle flux.
Moreover, without information on the natural changes, it would be
impossible to see variations resulting from an impact.
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