Energy flow on Georges Bank revisited: the energy modeling and analysis exercise (EMAX) in historical contexts

Abstract

We developed a mass balance ecosystem network model for Georges Bank, a highly productive and intensively studied marine system located off the New England coast. This effort is part of a broader initiative, the Energy Modeling and Analysis eXercise (EMAX), to describe ecosystem characteristics of major ecoregions of the Northeast Continental Shelf of the United States. Energy budgets for this system developed over the last six decades have progressively increased in complexity. Our analysis is based on a 33 compartment model, ranging from phytoplankton to marine mammals, seabirds, and humans for the period 1996–2000. Levels of primary production on the Bank are high relative to many other continental shelf ecosystems. Analysis of mixed trophic impacts indicates the pervasive influence of primary producers throughout the system, indicative of a system subject to important bottom-up forcing. We demonstrate the importance of the microbial food web in energy flow in the system, indicated by high levels of throughput for this component. Our analysis differs from previous energy budgets for Georges Bank in providing substantially higher estimates of zooplankton production, producing a different perspective on what had been perceived as a lower than expected ratio of secondary to primary production that was attributed to export processes. Relative species composition of the fish community differed markedly in our analysis relative to previous energy budgets for this system, with a dominance by small pelagic fishes. Despite these differences, the estimated biomass levels were roughly comparable to those from prior studies. Estimates of system developmental capacity and overhead suggest a highly resilient system.