Euphausiid crustaceans (krill) are a critical source of carbon in marine food webs, providing food for hake, Chinook and Coho salmon, rockfishes, seabirds and large whales. Yet, despite their ecological importance, little is known about euphausiid spatial and temporal distribution, abundance and reproductive dynamics. This project will examine the relationship between seasonal changes in physical oceanographic conditions and the distribution and abundance Euphausiid pacifica and Thysanoessa spinifera in the Gulf of the Farallones-Cordell Bank region. A series of research cruises will help scientists test the hypothesis that coastward advection of cold, salty bottom water during intense upwelling pushes the more oceanic species, such as E. pacifica, onto waters on the continental shelf where they become an abundant, earlyseason food source for predators. As upwelling relaxes, T. spinifera (a coastal species) increases in its relative abundance. Findings from this project have many applications, an important one being the potential to assist with an ecosystem-based approach to fisheries management.