Evaluation of carbon pathways supporting the diet of invasive Hemimysis anomala in a large river

This study is providing the first insight on the food sources supporting Hemimysis anomala in a lotic ecosystem where food webs differ from those of lentic ecosystems. Using carbon and nitrogen stable isotopes, the diet of Hemimysis was evaluated in multiple sites of the St Lawrence River where higher density swarms have been recently reported. We found that Hemimysis may feed on multiple food sources, including benthic and pelagic production, and from multiple trophic levels. Results from a mixing model applied to evaluate the importance of benthic versus pelagic food sources revealed site specific variations in diet. At the low flow sites located in the Montréal Harbour, Hemimysis fed primarily on pelagic production compared to the more open sites exposed to higher flow located outside of the harbor. This study indicates that Hemimysis may adapt its feeding behavior to environmental conditions and/or food source availability, potentially increasing its impacts on food web structure.

► Hemimysis is able to use both benthic and pelagic carbon sources as a food resource.
► Under reduced flow condition, pelagic carbon was Hemimysis preferred food source.
► In more exposed sites of the harbor, benthic food source was preferred.
► Food preference was poorly related to body size and population composition.
► This feeding behaviour may increase Hemimysis impacts on food web structure.