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the bottom. Different sampling devices were used to obtain fauna of
different sizes. Other types of gear were put on the bottom for long-term
monitoring, in a multidisciplinary autonomous vehicle.
For the ecology of the deep sea, IFREMER had chosen to work with
three types of gear that were more or less standard. However, there was no
standard method for collecting megafauna. French scientists used a beam
trawl with a wooden beam 6 metres long, which primarily collected
epibenthic fauna, mostly invertebrates. For sampling fish, much better
trawls existed. Although megafauna were collected qualitatively, there was
no good sampling strategy for quantitative sampling. The USNEL box corer,
developed by the United States Naval Electronic Laboratory and initially
used by P.A. Jumars and R.R. Hessler in the 1970s, was now internationally
regarded as standard because its large box was relatively well sized for
sampling the small components of the deep-sea benthic fauna. It was also
important to sieve correctly the sediment collected with this box corer in
order to sample small macrofauna. Researchers could be given a lot of
discretion on the sieving levels, because much knowledge was available in
the literature. Since 1976, IFREMER had decided to sieve at a mesh size of
250 microns. The multiple corer, which her group had been using for about
10 years, was being used not only for meiofauna at a 40-µm mesh size but
also for bacteria and for the chemical compounds in the sediment.
In order to study the structure of the benthic community according
to size, it was important to agree on the various types of gear, as each type
was suitable for a different component of the fauna. The multiple corer
might be used mainly for microbiota, the USNEL box corer had a limiting
size of 250 µm for macrofauna, and the beam trawl was usually sieved at 1
centimetre.
In sieving, the gear must be chosen according to the taxa to be
collected. For example, the USNEL box corer was used for macrofauna,
while meiofauna were better collected with the multiple corer. Of course,
nematodes and harpacticoids were picked up in the box core, but they were
excluded from counts in order to achieve quantitatively correct samples.
Among megafauna, specimens of many different large invertebrates and
fish were needed in order to study the trophic behaviour of various species.
These had to be defined at the species level to identify any changes due to
impact, for example. Therefore, any research programme had to depend on
progress in taxonomy, combining classic taxonomy based on the Linnaean
system with molecular biology. Otherwise, too many errors would result.
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