Predicting bioaccumulation in dynamic food webs: Ontogeny, seasonality and invasional successions

The structure of aquatic food webs has changed dramatically at the global scale. Overfishing, persistent chemical contamination, and the rapid spread of non-indigenous species have caused the loss of the "big fish"-traditional predator species that once formed the basis of the fishing industry. This decline in pelagic diversity, coupled with the effect of invasive species like the zebra mussel, has led to the benthification of many aquatic systems, particularly in the Great Lakes. Often, the interactions between chemical contaminants and invasive species in these dynamically altered, benthified food webs have unexpected consequences. Yet, management and restoration strategies for such systems are based on the contaminant transfer patterns observed in pelagic food webs. In pelagic systems, contaminant levels increase with increasing trophic level, such that the largest predator fish are the most contaminated - a trend that often conforms to the persistent, yet overly simplified, notion of a "food chain." We have developed a modeling strategy that combines a seasonal, stage-structure food web model with a fugacity-based Mackay type bioaccumulation model to predict contaminant fate in food webs under "trophic flux" via seasonal diet changes, ontogeny, or invasional succession. We show how changes in species' diets lead to complex trophic dynamics, even in seemingly simple food webs, often creating contaminant feedback loops that change bioaccumulation patterns in unexpected ways, with profound implications for ecosystem management strategies and for the minimization of human health risks from fish consumption.