Zooplankton displacement volume measurements for Arabian Sea Cruise TN039, Training and calibration cruise, Singapore to Muscat

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 one meter Multiple
Opening\Closing Net and Environmental Sensing System (MOCNESS) fitted
with 149 um 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 a further description of the 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 35
meters/minute during deployment and 5 to 20 meters/minute during
recovery.  On board the ship, samples were 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 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.