Invasive species impacts on ecosystem structure and function

Exotic species invasion is a worldwide threat to the integrity of aquatic ecosystems. To understand ecosystem level response to the introduction of exotic species, I compared food web characteristics of two eutrophic Great Lakes ecosystems - the Bay of Quinte, Lake Ontario, Canada, and Oneida Lake, New York, USA - before and after zebra mussel (Dreissena polymorpha ) invasion using ecological network analysis (ENA) and a social network analysis method, cohesion analysis (CA). ENA quantifies ecosystem function through an analysis of food web transfers, while CA assesses ecosystem structure by organizing food web members into subgroups of strongly interacting predators and prey. In Oneida Lake and the Bay of Quinte, zebra mussel invasion increased food web organization and the potential for system development. Additionally, zebra mussel invasion stimulated benthic production in both systems. Effects on food web structure were strongest in the Bay of Quinte where zebra mussel invasion removed subgroup structure entirely. In Oneida Lake, over 33% of taxa changed subgroup association after invasion, with benthically associated subgroups gaining the most members. This analysis suggested that the effects of zebra mussel introduction are similar in ecosystems of comparable trophic status and that future invasions of eutrophic systems could have similar impacts on ecosystem structure and function.