Biomass flows between pelagic predator communities in the California Current

The spatial distribution of upper trophic levels emerges from the interaction of a multitude of biotic and abiotic processes. Size-based models reproduce the complexity of these interactions with a limited number of parameters, building on mechanistic, size-dependent representations of metabolism and predator-prey dynamics. These models reproduce biomass flow within pelagic communities, from small larvae to large top predators, forced by environmental variables, including temperature and primary production. We present a size-based model of the California Current Ecosystem developed to resolve spatial biomass exchanges due to passive transport by currents, active swimming, and interactions along the water column. The model, APECOSM-CC, tracks the three-dimensional biomass flow, from plankton to top predators, for three interacting communities: epipelagic, mesopelagic, and vertical migrants. We constrain the model with trawl and acoustic observations, and force it with a realistic simulation of the physical-biogeochemical dynamics of the California Current. We use the model to close the biomass budget of upper trophic levels in 15 biogeochemically-coherent eco-regions, comparing the roles of production, transport, movement, and trophic interactions. The study reveals the sources and sinks of predator biomass in the California Current, and how they relate to their environmental drivers.