Hemimysis anomala in Lake Ontario food webs: Stable isotope analysis of nearshore communities

Abstract

Hemimysis anomala, a littoral freshwater mysid native to the Ponto-Caspian region, is the newest invader to the Laurentian Great Lakes basin. Discovered in 2006, they have since been found in all of the Great Lakes (except Lake Superior) and have the potential to offset the dietary energy sink caused by invasive dreissenid mussels (Dreissena bugensis and D. polymorpha) in the littoral zone. We evaluated nearshore food web structure at four sites along Lake Ontario's north shore spanning a gradient of Hemimysis density to determine: 1) if dominant nearshore food web pathways change seasonally, and 2) whether fish are exhibiting a dietary shift towards consumption of Hemimysis. No Hemimysis were found in any of the 431 fish (alewife Alosa pseudoharengus, round goby Neogobius melanostomus, and yellow perch Perca flavescens) stomachs analysed. We used stable isotopes of carbon (13C) and nitrogen (15N) collected from invertebrates and fish to characterise trophic linkages and fish dietary preference. Yellow perch and round goby exhibited significantly higher Δδ15N at Bronte (high Hemimysis density) compared to Cobourg, Waupoos and the Bay of Quinte. Δδ13C of alewife is more enriched at Bronte and is comparable to the Δδ13C of Hemimysis. Our results suggest that Hemimysis are being incorporated into diets of round gobies, alewife and small yellow perch and their reliance on Hemimysis as a dietary component increases with Hemimysis density. As Hemimysis populations continue to establish and stabilize, fish may incorporate this species into their diets at a higher rate.