AbstractThe two species Thysanoessa raschii and Meganyctiphanes norvegica dominate the krill biomass of the Estuary and Gulf of St. Lawrence (EGSL) ecosystem. The EGSL is the southernmost limit of seasonal sea-ice cover in the North Atlantic and constitutes a dynamic frontier between Arctic and Atlantic water masses. In order to better understand the complex mechanisms underpinning the spatio-temporal dynamics of the production and distribution of these keystone forage species in the EGSL, we coupled in a Lagrangian framework an individual-based model (IBM) of krill physiology to a three-dimensional regional circulation model and a NPZD-type biogeochemical model. Our results show that the spatio-temporal production dynamics of both krill species was principally controlled by their food dynamics. Our numerical analyses highlighted the potential areas of krill production within the EGSL during spring and summer. We confirmed that the St. Lawrence Estuary was the most productive area, and we show that it subsidizes the central and southern Gulf during most of the growing season. The Estuary is part of a larger cyclonic circuit of krill production and transport that runs along the shores of most of the EGSL and the slope of the Laurentian Channel.