PI: Sharon Smith
of: University of Miami
dataset: Zooplankton displacement volumes from Bongo tows
dates: November 30, 1995 to December 26, 1995
location: N: 22.5043 S: 12.0746 W: 57.3059 E: 68.769
project/cruise: Process 5 TN050, Arabian Sea (Late SW Monsoon)
ship: R/V Thomas Thompson
Sharon L. Smith
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Causeway
Miami, FL 33149
Arabian Sea Expedition THOMAS G. THOMPSON TTN050
nd indicates No Data
Stations 28, 29 and 31 have no corresponding Standard Stations
Sta 5; net = 153 um; Approximately 20% of sampled spilled in lab,
vol_disp corrected accordingly.
Sta 15; both nets; Flowmeter failed, therefore vol_net estimated from
regressing vol_filt with the time in the water of other Bongo tows with this net.
Sta 19; net = 335 um; 1 crab, 7 cc. measured separately.
Sta 25; net = 153 um; 1 crab removed from sample at sea, 10 cc.
Sta 25; net = 153 um; Flowmeter data for this sample was suspiciously low,
therefore the volume filtered for the paired 335 um net was applied here.
Sta 27; net = 153 um; 1 crab removed from sample at sea, 40 cc.
Sta 28; net = 335 um; Flowmeter data for this sample was suspiciously low,
therefore the volume filtered for the paired 153 um net was applied here.
Sta 29; net = 153 um; 1 crab removed from sample at sea, 12 cc.
Sta 30; net = 153 um; 1 crab removed from sample at sea, 8 cc.
Zooplankton displacement volume measurements of Bongo samples collected during Arabian Sea Cruise TN054 (Process Cruise 7).
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 60 cm diameter 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 maximum sampling
depth of each tow was determined from a Wildlife Computers Mk3e Time
Depth Recorder (TDR) attached to the net frame.
The Bongo nets were towed beside 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, samples from the 153 um net were split in a modified Folsom
Splitter which split the sample into four parts consisting of 50%, 20%,
20% and 10%. In general, 10% was used for dry weight measurements, 20%
was preserved for collaborating scientists (Prell, McDonough) and 70%
was preserved for displacement volume measurements and taxonomic
analysis. The portion of each sample for dry weight measurement was
poured through nested sieves of 1050, 560, 200 and 64 um mesh. Each
size fraction was then placed on a pre-weighed 9 cm Whatman #1
qualitative filter. The filters were stored in glassine envelopes and
placed in a drying oven at 55 to 6 degrees C. Near the end of the
cruise the dry weight samples were sealed in cracker tins with
desiccant for transport to the laboratory where they were later weighed
on a Mettler H20 balance. The samples from the 335 um nets were
briefly scanned under a Wild M5 dissecting microscope on the ship to
assess the dominant zooplankton taxa and then preserved in their
entirety in 4% buffered formaldehyde/seawater for laboratory
measurement of displacement volume.
In the laboratory, displacement volumes 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.
The size specific dry weights from the 9 cm filters are reported in
units of mg/m^3. The size ranges are labeled in the data file as
zp_dw_1, zp_dw_2, zp_dw_3, zp_dw_4 and zp_dw_T, and correspond to size
fractions of 64-200 um, 200-560 um, 560-1050 um, greater than 1050 um
and total dry weight which is the sum of the four size fractions. It
is important to note that these size ranges are not identical to those
reported by Wishner or Roman for other cruises and samples.
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.
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