Quantifying Mechanisms for Zebra Mussel Effects on Benthic Macroinvertebrates: Organic Matter Production and Shell-Generated Habitat

Abstract

Quantitative descriptions of interactions between zebra mussels (Dreissena polymorpha) and other organisms are needed for an understanding of zebra mussel effects on energy flow and community dynamics in North American freshwater ecosystems. We used a field experiment to quantify effects of 2 potential mechanisms for increasing benthic macroinvertebrate biomass and densities in the Great Lakes following the zebra mussel invasion: 1) habitat created by zebra mussel shells, and 2) habitat and food provided by increases in benthic organic matter. Macroinvertebrate biomass, macroinvertebrate densities, and organic matter mass (hereafter termed organic matter) were measured on substrates (tiles without zebra mussels, with zebra mussel shells, and with live zebra mussels) that were held in western Lake Erie for 37 d. Organic matter was 3×-5× greater on tiles with live mussels than on plain tiles or tiles with shells, demonstrating that filter-feeding zebra mussels increased organic matter on benthic substrates. Organic matter did not differ on tiles with shells and tiles without mussels. Similarly, total macroinvertebrate biomass was 2×-5× greater on tiles with live zebra mussels than on tiles with shells and tiles without mussels; however, macroinvertebrate biomass also was 3X greater on tiles with shells than on tiles without mussels. Habitat created by shells was the most important cause for zebra mussel-generated increases in total macroinvertebrate biomass and densities of Hydridae, Dugesia tigrina (Turbellaria), Physella sp. (Gastropoda), Gammarus fasciatus (Amphipoda), and Microtendipes pedellus (Chironomidae). However, organic matter produced by zebra mussels also caused increases in total macroinvertebrate biomass and densities of Physella and Microtendipes. Zebra mussels did not reduce densities of any macroinvertebrate taxon. Because benthic macroinvertebrates are important prey for crayfish and benthivorous fishes, increases in macroinvertebrate abundance may be important in channeling energy from zebra mussels to higher trophic levels in the Great Lakes.