Zooplankton displacement volume measurements for 
Arabian Sea, Cruises TN050, TN054 (Process Cruise 5 and 7).

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


Zooplankton samples were collected using a double one meter Multiple 
Opening\Closing Net and Environmental Sensing System (MOCNESS) fitted with 
153um Nitex nets.  The nets fished with an open area of approximately one 
square meter.  A flow meter mounted on the frame, just ahead of the net as it 
fished, measured the distance towed to allow the calculation of volume 
filtered.  (See Wiebe et al, 1976 and 1985 for further documentation of the 
original MOCNESS).

The MOCNESS was towed behind the ship at approximately 1.5 to 2 knots through 
the water.  Winch speed usually ranged from 10 to 25 meters/minute during 
deployment and 5 to 15 meters/minute during recovery.  On board the ship, 
samples were either split and 50% preserved or the entire sample was preserved
in 4% buffered formaldehyde/sea water for transport to the laboratory.

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 250, 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.

Wiebe, P. H., K. H. Burt, S. H. Boyd, and A. W. Morton, A multiple 
opening-closing net and environmental sensing system for sampling zooplankton,
J. Mar. Res., 34, 312-326, 1976.

Wiebe, P. H., A. W. Morton, A. M. Bradley, J. E. Craddock, T. J. Cowles, V. A.
Barber, R. H. Backus, and G. R. Flierl, New developments in the MOCNESS, an 
apparatus for sampling zooplankton and micronekton, Mar. Biol., 87, 313-323, 
1985.