Background/Question/Methods As the largest embayment of Lake Michigan, Green Bay is a historically important ecosystem and plays a large role in the overall ecological and economic productivity of this Laurentian Great Lake. Dreissenid mussels successfully colonized Green Bay in 1993 and have flourished in the system ever since. Our recent studies have documented increased Chlorophyll a, phytoplankton abundance and dominance by cyanobacteria in the system following the invasion, but the question of whether there have been corresponding changes in net primary production of this system have remained untested. In addition, the ecological consequences of these changes for trophic interactions and transfer efficiencies in the ecosystem have yet to be determined. To address these questions we determined net primary production (using the carbon-14 uptake method) and zooplankton community grazing rates (using carbon-14 labeled algae uptake studies) during two post-invasion years along the strong trophic gradient in the bay. Results/Conclusions Net primary production was higher in the two post-invasion years compared to published results from the pre-invasion period using the same methods. Community grazing rates were higher overall as well, but there was a shift in the seasonal timing of peak grazing, with lower late summer grazing compared to the pre-invasion period. These changes correspond to shifts in the species composition and abundance of the zooplankton community. The data indicate that both alterations in phytoplankton community composition as well as changes in fish predation on plankton following the invasion have led to modifications of zooplankton grazing rates and lower food web trophic interactions in this highly productive ecosystem.