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2.6. Zooplankton
Depth-stratified sampling over the water column can be carried out
most efficiently with a BIONESS (Biological Net and Environmental Sampling
System) or MOCNESS (Multiple Opening and Closing Net and Environmental
Sensing System) with nine or ten nets, mouth opening 1 m 2 and mesh size
200 ? m. The sampler is lowered while underway to within 25 m of the
bottom and then towed obliquely upward so that nets sample the following
depth horizons:
Net
1: Surface – bottom-25 m
2: Bottom – 25-2000 m
3: 2000-1000 m (or base of O2 minimum layer)
4: 1000-500 m
5: 500-200 m
6: 200-0 m.
Two tow series will be carried out in daylight hours at each station
and two at night.
Zooplankton sampling procedures follow the Zooplankton
Methodology Manual published by the International Council for the
Exploration of the Sea (ICES) 20 . A flow meter, calibrated before and after
each cruise, is placed in the mouth of the net. Larger gelatinous
zooplankton are removed, identified, enumerated and their volume
measured prior to sample fixation. Samples are fixed in 4 percent buffered
formaldehyde. In the laboratory, displacement volume is measured and
aliquots counted so that at least 300 organisms are enumerated, by genus
where possible.
Microzooplankton, defined as organisms less than 200 ? m in
length, are sampled from the Niskin bottles during the standard rosette
sample casts and at the standard depths. One-litre samples are fixed with
Lugol’s solution and examined after allowing the organisms to settle on a
settling chamber so that they can be enumerated with an inverted
microscope.
2.7. Micronekton
The micronekton can be sampled using a MOCNESS-10, a system
with six nets, a 10-m 2 mouth opening and a 3-millimetre mesh. The same
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