Krill hotspots in a moving ocean: environmental drivers and ecosystem significance

In pelagic ecosystems, linkages between phytoplankton, zooplankton, forage fish and higher trophic level predatory species must be considered in a context where local, regional and global scale ocean currents continuously reshape and rescale the underlying physical and biological environments. In the California Current Ecosystem (CCE), one of the four major eastern boundary current upwelling regions, krill (euphausiids) represent a key link between primary production and higher trophic level species due to their central position in the food web and tendency to form dense aggregations. Results from a coupled physical-biogeochemical model offer unique insights into the fundamental biophysical processes that shape ecosystem response in the CCE across space and time. Not only does the model solution effectively recreate the location of known krill hotspots and their relationship to coastal upwelling, but it also provides a comprehensive view of their seasonal and interannual evolution, sensitivity to alongshore variations in primary productivity and ocean currents, and connection to observed distributions of whales and seabirds. Furthermore, the model suggests that the dynamics controlling krill hotspot formation and persistence in the CCE are strongly heterogeneous in space and time and must be understood in the context of local alongshore variations in coastal upwelling modulated by regional and climate scale influences.