An overview of the impact of non-indigenous species on the food web integrity of North American Great Lakes: Lake Erie example

Abstract

For the past several decades, the North American Great Lakes have suffered from eutrophication. The deteriorating state of the Great Lakes alarmed both the governments of Canada and the United States resulting in the Great Lakes Water Quality Agreement, which has brought about substantial improvements in water quality. While phosphorus abatement resulted in a significant decrease in nutrients, the sudden invasions of exotic species posed a serious threat to Great Lakes food webs. The zebra mussel (Dreissena polymorpha) and the quagga mussel (D. bugensis), followed by other exotic species, infested Lakes Erie and Ontario causing a drastic reduction in phytoplankton biomass and increasing water clarity. In Lake Erie, post-Dreissena declines in phytoplankton size structure and changes in community composition were observed in this study, along with significant declines in primary productivity in the west basin. At the other end of the food web, exotic species such as alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax) and white perch (Morone americana) have become important to the Lake Erie commercial fishery, while other native fish species have declined. This paper presents an historical perspective and a general overview of the impact of nonindigenous species in the North American Great Lakes from the base of the food web to the fisheries. Lake Erie has been chosen as a case study to provide a detailed treatment. The expansion and growth of nonindigenous species has been responsible for significant modifications to the structural and functional characteristics of the food webs and fisheries of the Great Lakes. Our experience demonstrates the significance of the impact of exotics and the need to manage this serious problem on a global basis so that the integrity of food webs and fisheries throughout the world can be protected.This paper is dedicated to Dr. Jack Vallentyne for his contributions to Great Lakes research, especially for the implementation of the ‘ecosystem approach’. These contributions were in evidence in revisions to the Great Lakes Water Quality Agreement and more currently in the management of exotic species.