This project constitutes a portion of U.S. joint global ocean flux study (JGOFS) of the central equatorial Pacific. Several observations have been made in this region which contradict some of our conventional concepts of trophic status and the relationship between plankton community structure and vertical flux. High nitrogen concentrations and supply rates, usually associated with eutrophic conditions, co-exist with relatively low chlorophyll, primary productivity, and "new production" - which are characteristics of oligotrophic waters. Smaller pico- and nanoplankton cells dominate the phytoplankton (Chavez, et.al. in press), yet significant rates of biogenic sedimentation occur and is correlated with primary production. High flux rates are usually thought to be associated with large cells, such as diatoms, sinking out of surface waters or being consumed by larger cells, fecal pellet-producing metazooplankton. These apparent contradictions indicate that the consequences of phytoplankton size structure, protozoan versus metazoan grazing, and their relationship to vertical flux of material out of the surface layer are not fully understood. This project will examine these contradictions by measuring the abundances and biomass of the phototropic picoplankton, phototrophic and heterotrophic nanoplankton, and phagotrophic protozoans in the surface water, and the grazing impact and growth rates of protozooplankton. We study will employ proven, state-of-the-art color image analysis combined with epifluorescence microscopy to describe the size, trophic and taxonomic structure of the plankton. Results will be used to determine the role of protozoan zooplankton in the coupling of production, consumption and export of particulate of particulate organic matter in the surface waters of the central equatorial Pacific.
