The California Current System (CCS) owes its high phytoplankton productivity to wind-driven circulation patterns that bring nutrient?rich waters to the surface. These high rates of primary productivity are translated via high zooplankton secondary productivity, into high biomass of epipelagic fishes such as anchovies, hake, and salmon. Further, spatial patterns of high primary and secondary productivity are heterogeneous and appear to be closely linked to mesoscale physical structures (e.g., filaments, jets, and eddies). Using a series of linked physical/ecosystern/zooplankton models, this study will examine the complex interaction of physical and biological processes (diel vertical migration and growth efficiency) in the CCS on seasonal and interannual time?scales. Major calanoid copepods (e.g., Calanus pacificus and Metridia pacifica) and euphausiid species (e.g., Euphausia pacifica and Thysanoessa spinifera) that represent critical linkages between primary production and salmon populations will be emphasized. In addition, the roles of these processes will be further illuminated through comparative studies with other ecosystems located within both similar and dissimilar dynamical environments. The goal of this study is to address the following questions: How does the circulation field impact the distribution and population success of major CCS zooplankton species such as C. pacificus, M. pacifica, E. pacifica, and T. spinifera? How do the behavioral and bioenergetic differences of these species interact with the circulation field, prey distribution and temperature to influence their relative population success? How does the interannual variability of the local environment (e.g., from large?scale atmospheric or oceanic fluctuations) modify these distributions and relative success of major CCS zooplankton species? How do physical and biological aspects of the CC/Zooplankton System compare to other well?studied ecosystems including those of particular interest to GLOBEC (e.g., Georges Bank, Gulf of Alaska, and Southern Ocean)? The results of this study will include the developed ecosystem and zooplankton models, applied within regional and basin?scale circulation models. The coupled systems will be analyzed under seasonal and realistic surface forcing closely tied to CCS process studies. Furthermore, a comparative synthesis of physical and biological coupling within this and other well?studied GLOBEC ecosystems will begin.