Mesozooplankton Grazing Rates Measured during the JGOFS Equatorial Pacific Process Study

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 "usjgofs.whoi.edu/jg/dir/jgofs/" [The information in this summary was derived from the JGOFS World Wide Web pages.]