Role of the Invasive Bloody Red Shrimp Hemimysis anomala in the Nearshore Foodweb of Lake Ontario

Hemimysis anomala, a Ponto-Caspian mysid, is an emerging Great Lakes invader that was discovered in both Lakes Michigan and Ontario in 2006, and has since spread to Lakes Erie and Huron, and inland NY waters.  Similar to the native mysid, Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern, but generally inhabits shallower and warmer waters than M. diluviana.  During 2009-2010 we sampled an in-lake population of Hemimysis in southeastern Lake Ontario monthly from May-November at depths 4m – 20m, and conducted laboratory experiments on light, substrate, temperature, and prey selection.  We observed seasonal and annual variation in abundance, and recorded the species at <20 m water depth.  Hemimysis produce multiple cohorts per year, and have a wide temperature tolerance; both characteristics could facilitate population expansion in invaded ecosystems.  However, use of substrate and vertical migration patterns of Hemimysis are likely influenced by predation pressure, which may limit dispersal.  Laboratory results indicated that size and mobility of prey items influenced Hemimysis prey selection, but analysis of field collected Hemimysis diets showed the species to be omnivorous, with an ontogenetic shift from more plant material to more animal material.  Stable isotope analyses indicate that Hemimysis use both pelagic and littoral plant sources for energy, and also likely consume small zooplankton.  Hemimysis were found in diets of alewife, yellow perch, rock bass, cisco, and white perch.  Consumption of Hemimysis by fish varied seasonally and annually and was related to abundance patterns of the species in the environment.  Results of this project indicate that Hemimysis has the potential to play an important role in energy transfer in nearshore foodwebs where they are abundant.