Mesozooplankton Grazing Rates Measured during the JGOFS Equatorial Pacific Process Study

The Equatorial Pacific Process Study (EQPAC) was conducted along 140 deg W
longitude during 1992.

Four cruises took place: February 3 - March 9, March 19 - April 15,
August 5 - September 18, and September 24 - October 21. A fifth benthic
cruise and sediment trap legs were added. During the first cruise
(TT007), 15 stations were occupied along 140 deg W longitude from
12 deg N latitude to 12 deg S latitude. During the second cruise
(TT008), data were collected at 8 stations along 140 deg W longitude
from 9 deg S latitude to 9 deg N latitude. During the third cruise
(TT011), data were collected at 15 stations along 140 deg W from 12 deg N
latitude to 12 deg S latitude. During the fourth cruise (TT012), data were
collected at 5 stations along 140 deg W longitude from 17 deg S
latitude to the equator.

To measure zooplankton grazing rates, vertical tows for
zooplankton were conducted day and night with opening-closing 3/4
meter Puget Sound nets with 200 micrometer mesh. Three depth strata
were towed: 0-20 m, 20-60 m, and 60-120 m. The net contents were
sieved into three size fractions: 2.0 - 1.0 mm, 1.0 - 0.5 mm, and 0.5 -
0.2 mm. Triplicate subsamples of 30-100 animals were picked from the
samples without regard to species and placed in centrifuge tubes with
90% high-grade cold acetone solution. A similar number of animals per
sample were also picked for weight (C,N) determination. The amount of
pigment per individual was measured fluorometrically and expressed as
chlorophyll per body carbon. Using gut pigment values and gut
passage time (which was estimated from the reciprocal of gut clearance
rate constant which was estimated with every collection), pigment
ingestion was calculated. The grazing impact of zooplankton was then
estimated from the product of weight-specific pigment ingestion and
biomass for each size class. Units for grazing rate are in mg pigment
/ (mg body carbon hour).

The data is public domain and can be retrieved on-line at
"http://usjgofs.whoi.edu/jg/dir/jgofs/"

[The information in this summary was derived from the JGOFS
World Wide Web pages.]