Zooplankton displacement volume measurements of Bongo samples collected during Arabian Sea Cruise TN050 (Process Cruise 5).

Sharon L. Smith
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Causeway
Miami, FL  33149


Zooplankton samples were collected in oblique Bongo net tows which
covered approximately the upper 200 m of the water column.  The Bongo
frames were either 61 cm diameter (Wishner) or 60 cm diameter (Smith)
and were fitted with 153 and 335 um Nitex nets.  A General Oceanics
flow meter model 2030R was secured in the net mouth  for the
determination of volume filtered.

The Bongo nets were towed behind the ship at approximately 1.5 to 2
knots through the water.  Winch speed was generally 30 meters/minute
during deployment and 20 meters/minute during recovery.  On board the
ship, the samples from the 153 um net were split and half used for
determination of carbon (Roman), dry weight (Wishner) and ash-free dry
weight (Wishner).  The other half was preserved in 4% buffered
formaldehyde/sea water for transport to the laboratory for displacement
volume measurement and taxonomic analysis. The samples from the 335 um
nets were similarly split and half used for dry weight analysis
(Wishner) and the other half preserved for displacement volume
measurements.

In the laboratory, the displacement volumes of the samples were
determined following the methods described by Ahlstrom and Thrailkill
(1963), and Kane (1982).  In general, samples were poured into 500 or
1000 ml graduated cylinders, depending on the volume of plankton
present, the volume of plankton and water was measured, then the sample
was poured through a 150 um sieve, allowed to drain, and the volume of
water measured.  The difference between the two volume measurements was
the displacement volume.  The displacement volume of each sample was
divided by the volume filtered by the net (m^3) and the result is
reported here in units of cc/m^3.

References

Ahlstrom, E. H. and J. R. Thrailkill, Plankton volume loss with time of
preservation, Rep. 9, pp. 57-73, Calif. Coop. Oceanic Fish. Invest., La
Jolla, 1963.

Kane, J., Effect of season and location on the relationship between
zooplankton displacement volume and dry weight in the Northwest
Atlantic, Fish. Bull., 80, 631-642, 1982.