Modeled population biology of Euphausia pacifica in the California Current using the Regional Ocean Modeling System Coupled with an Offline Individual-Based Model.

Euphausia pacifica is the dominant krill species on the West coast of the United States and an important trophic link in the food web of the coastal upwelling ecosystem. Understanding the impacts of physical forcing on their spatial distribution and biological condition will enable a better understanding of the productivity of those predators that rely on them as a food source. We have chosen to use an individual-based model (POPCYCLE) to simulate E. pacifica as there are known aspects of their life-history that are difficult to model using a traditional concentration based model or other available individual-based models. Those aspects include, diel-vertical migration, discreet reproductive events, and stage-specific mortality and growth. The IBM POPCYCLE is run offline from ROMS, allowing multiple population simulations without the computational expense of running ROMS, but interpolation between saved forcing data must be implemented. We present results of the spatial and temporal distribution from the winter/spring of 2001 and 2005 in the California Current. The year 2001 was chosen as a fairly “standard” year for the California Current; and the year 2005 was simulated as an anomalous year, i.e., upwelling was delayed much later in the year than on average. Results show that changes in advection and phytoplankton abundance impact the spatial and temporal peaks of Euphausia pacifica abundance and reproductive effort. These model results provide information on the factors that control important prey species productivity in the California Current.

Dorman, Jeffrey - UC Berkeley, Berkeley, CA
Powell, Thomas – UC Berkeley, Berkeley, CA
Sydeman, William – Farallon Institute, Petaluma, CA
Bograd, Steven – NOAA, Southwest Fisheries Science Center, Pacific Grove, CA