**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

 

 

Quantifying the impact of exotic invertebrate invaders on food web structure and function in the Great Lakes: A network analysis approach

Doran M. Mason ¹

¹GLERL-NOAA

2205 Commonwealth Blvd.

Ann Arbor, MI 48105

 

Ann E. Krause ²

² Dept. of Fisheries and Wildlife

Michigan State University

East Lansing, MI 48824-1222

Current Address: Department of Environmental Sciences, University of Toledo, Toledo, OH 43606

 

A. Jaeger³

³ Dept. of Fisheries and Wildlife

Michigan State University

East Lansing, MI 48824-1222

R. Ulanowicz⁴

⁴ Chesapeake Biological Laboratory

Solomons, MD 20688

Abstract

We examined the food-web structure and function of southeast Lake Michigan, Oneida Lake New York, and the Bay of Quinte Ontario to determine the ecosystem level impacts of species invasion. For Lake Michigan, we tested for changes in food web compartmentalization and measured food web structure using four indices: weighted connectance, quantitative connectance, diversity of interactions, and diversity of taxa. We found that the structure
of the food web was significantly compartmentalized, where the compartments represented a range of biotic habitats. Connectivity and diversity of interactions were greater within compartments than between compartments. The overall food web structure demonstrated resistance to the invaders in compartment membership and three of its indices. The fourth index, quantitative connectivity, demonstrated a detectable decline from its pre-invasion status.
This decline indicated that those taxa with large biomass in the post-invasion structure had fewer effective interactions than those in the pre-invasion structure, providing fewer effective interactions as alternative pathways to absorb disturbance affects. These fewer effective interactions could act as buffers for unaffected compartments from the disturbance with fewer pathways to transfer the effects. For Oneida Lake and the Bay of Quinte we also
tested for changes in compartmentalization in the food web following invasions, but also integrated ecological network analysis (ENA) indices to determine the affects of invasions on ecosystem function. The combined methods detected direct and indirect impacts, changes in trophic flow efficiency, and alterations of food web organization and ecosystem activity resulting from zebra mussel invasion. ENA indicated that zebra mussels
altered food web function by shunting energy from pelagic to benthic pathways (e.g., macrophyte and detrital production increased), increasing dissipative flow loss, and decreasing ecosystem growth. Changes in the compartmentalization of the food webs suggested that zebra mussels altered food web structure by reorganizing carbon flow within and between discrete subgroups of predators and prey and also increasing the importance of
benthically associated subgroups. These analyses demonstrate that zebra mussels exert a strong influence on food webs and promote the benthification of aquatic ecosystems. Moreover, the current configuration of a food web (i.e., number and arrangement of compartments within a food web) may help to buffer the overall effects of species invasions on the entire ecosystem.