Modeling zooplankton growth in Lake Washington: A mechanistic approach to physiology in a eutrophication model

Many efforts have been made to incorporate our improved understanding of zooplankton physiology and behaviour into mathematical models. The increased complexity, however, has been a major impediment in integrating these advances into management-oriented models and thus bridging the gap between theoretical and applied ecology. In this study, we enhance an existing eutrophication model with a zooplankton somatic growth submodel that simulates the interplay among nitrogen, phosphorus, and highly unsaturated fatty acids (HUFAs) through the grazers’ digestive tracks. We calibrate the newly incorporated parameters (and associated processes) against observed data from the mesotrophic Lake Washington. We extrapolate the model to different trophic environments and tease out the underlying drivers of zooplankton growth. Our analysis suggests that both stoichiometric and HUFA based somatic growth limitations can modulate the zooplankton biomass in mesotrophic environments. Food abundance and mineral P limitation are critical factors of zooplankton growth under oligotrophic conditions, while HUFA availability is the main driving force of plankton dynamics in eutrophic states. Our zooplankton submodel downplays pre-gut regulation in favour of post-gut metabolic processing, which appears to shift the bulk of the non-limiting nutrient recycling from particulate to dissolved form. The homeostatic maintenance of somatic quotas and the dynamic nutrient recycling could also be an important mechanism for shedding light on the controversial hypothesis that the enrichment of natural ecosystems is a destabilizing factor of food web dynamics.