The central equatorial Pacific is an extensive region of high nutrient upwelling, enhanced primary productivity, and elevated plankton concentrations that is of special interest to the Joint Global Ocean Flux Studies (JGOFS) because it may account for 20 to 50% of the estimated global rate of carbon export to the deep sea. The general goal of this research is to contribute to understanding the relationships among primary production, food- web structure, and biogeochemical cycling and fluxes in this region as a component of the JGOFS Equatorial Pacific Program. The research utilizes a complementary set of experimental approaches (fluorescently-labelled prey particles, metabolic inhibitors, and seawater dilution) and flow cytometry techniques to identify major microconsumer groups and to measure their grazing rates, behaviors, and community impacts at different temporal and spatial scales. Specifically, the research will 1) determine the distributions, abundances, and biomass of pico- and nanoplankton communities and their variations with depth and latitude on cross-equatorial transects, 2) identify and quantify the dominant microzooplankton grazers on pico- and nanoplankton communities, 3) determine the grazing impact of microzooplankton on component populations of bacteria, prochlorophytes, cyanobacteria, and algae as functions of depth, time of day, and trophic state, 4) evaluate the hypothesis that there is a general size relationship linking the rates of grazing impact on picoplankton populations, and test the hypotheses that the role of mixotrophy among planktonic flagellates will increase along environmental gradients from eutrophic (nutrient-rich) to oligotrophic (nutrient-poor) systems and at low light levels in the euphotic zone.
