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We investigated how establishment of invasive dreissenid mussels impacted the structure and energy sources of the littoral benthic food web of a large temperate lake. We combined information about pre- and postdreissenid abundance, biomass, and secondary production of the littoral benthos with results of carbon and nitrogen stable isotope analysis of archival (predreissenid) and recent (postdreissenid) samples of all common benthic taxa. This approach enabled us to determine the importance of benthic and sestonic carbon to the littoral food web before, and more than a decade after dreissenid establishment. Long term dreissenid presence was associated with a 32-fold increase in abundance, 6-fold increase in biomass, and 14-fold increase in secondary production of the littoral benthos. Dreissenids comprised a large portion of the post-invasion benthos, making up 13, 38, and 56% of total abundance, biomass, and secondary production, respectively. The predreissenid food web was supported primarily by benthic primary production, while sestonic material was relatively more important to the postdreissenid food web. The absolute importance of both sestonic material and benthic primary production to the littoral benthos increased considerably following dreissenid establishment. Our results show drastic alterations to food web structure and suggest that dreissenid mussels redirect energy and material from the water column to the littoral benthos both through biodeposition of sestonic material as well as stimulation of benthic primary production.

From 2001 through 2004, the densities of Dreissena bugensis and Amphipoda (Gammarus fasciatus and Echinogammarus ischnus) decreased by 94% and 85%, respectively, in the rocky northern nearshore (2–10 m depth) zone of eastern Lake Erie. Densities of Chironomidae and Oligochaeta did not change. The decline in D. bugensis was most evident for individuals with shell lengths in the 3 to 14 mm range. The mean (±SD, n) abundance of round gobies (Neogobius melanostomus) at 10-m depth increased from 6.5 (± 1.9, 12)/m² in 2001 to 14(±1.0, 15/m² in 2002. Analyses of stomach contents in 2001 and 2003, and stable isotopes of carbon in prey and muscle tissue in 2002, indicated that the diet of round gobies in 2001 was predominately dreissenids, but that chironomids and amphipods became more important as the abundance of appropriately sized mussels declined. Round gobies collected in 2003 contained more individual prey, but less total mass of prey than did gobies collected in 2001. Our observations suggest that round gobies probably became food-limited in eastern Lake Erie by 2002. [ABSTRACT FROM AUTHOR]