**ABSTRACT NOT FOR CITATION WITHOUT AUTHOR PERMISSION. The title, authors, and abstract for this completion report are provided below. For a copy of the full completion report, please contact the corresponding author via e-mail at jerome.marty@genivar.com or via telephone at 613-363-0689. Questions? Contact the GLFC via email at frp@glfc.org or via telephone at 734-662-3209.**

Assessing the impacts of the invader Hemimysis anomala in multiple food webs of the Great Lakes basin using

stable isotopes and fatty acids

Jérôme Marty^{1, 2}, Yves de Lafontaine³, Marten A. Koops⁴, Michael Arts³ and Michael Power¹

¹Department of Biology, University of Waterloo, 200 University Ave. W., Waterloo, ON, Canada, N2L

3G1

²St. Lawrence River Institute, 2 St. Lawrence Dr., Cornwall, ON, Canada, K6H 4Z1

³Environment Canada – Centre Saint-Laurent, 105 McGill St.; Montréal, QC, Canada, H2Y 2E7

⁴Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, 867

Lakeshore Rd., Burlington, ON, Canada, L7R 4A6

ABSTRACT:

Invasive species are a known stressor on aquatic ecosystems, particularly in the waters of the Great Lakes basin. The most recent invader, Hemimysis anomala, has had significant impacts on the food webs of Europe, where it invaded previous to its spread to North America. This study used carbon and nitrogen stable isotopes to characterize and compare the diet of Hemimysis from 15 sites in the Great Lakes basin. Results indicated that: 1) Hemimysis relied predominantly on pelagic carbon sources at the majority of sites, and isotopic differences between life-stages existed at two of the 15 sites examined,2) the trophic position and reliance on pelagic food sources did not differ significantly between lotic and lentic sites, and 3) the isotopic niche width of Hemimysis was spatially heterogeneous, varying by an order of magnitude among sites, but was unrelated to the degree of isotopic variation in the basal food web at each site. Observed ranges in trophic offset and the pelagic fraction of dietary carbon indicate that Hemimysis derives carbon from both benthic and water column sources, as well as at multiple trophic levels. Our results support the notion that Hemimysis is a generalist consumer with pronounced dietary flexibility.