Effects of Nutrient Limitation on the Dynamics of an Estuarine Food Web

Estuaries are defined by their shifting salinity and nutrients, yet food web models rarely incorporate these impacts on producers. This study combined a box model of abiotic conditions with a food web model of trophic levels to study how nutrient limitation affects Chesapeake Bay biota. Using ac-tual data, the model tested the hypothesis that nutrient limitation affects lower trophic levels more than higher ones. Without nutrient limitation, the entire food web persisted with higher abundances of species directly feed-ing on trophic level one. Nutrient limitation reduced phytoplankton GPP, but those consumers not directly feeding on phytoplankton were hurt most by reduced GPP, counter to predictions. Additionally, the model predicts that reductions in silica suppress diatom populations, which again affects indirectly-linked species most strongly. The generally greater effects of nu-trient limitation, and corresponding GPP suppression, on species indirectly linked to phytoplankton may be due to a magnification of trophic transfer inefficiency along food chains. However, as the silica example shows, limita-tion of specific nutrients will have an asymmetric affect on the Chesapeake Bay food web because those species trophically linked to species dependent on the nutrient will be affected more than species not linked to affected pro-ducers. This model illustrates the utility of basing producer growth rates to actual nutrient fluctuations in given environments, a step toward realistic food-web modelling of Chesapeake Bay and other estuaries