Predicting the impacts of an invasive species on native food webs requires the integration of effective early detection methods, population analyses and controlled observations of predator-prey and competitive interactions in invaded ecosystems. In this study, we investigate the potential for key native and naturalized fish species of the Great Lakes and Hudson-Mohawk River watersheds (New York, USA) to capture a recent aquatic invertebrate invader, the bloody red shrimp (BRS), through controlled feeding experiments. After its first detection in North America in 2006, BRS has quickly spread and become established in the Great Lakes, St. Lawrence River and inland lakes of New York State, including Oneida and Seneca Lakes and has most recently become established in the Hudson River. In this study, we hypothesize that naturalized fish species, with important economic and ecological roles, utilize BRS as a food source and that fish species differ in their ability to both access and capture BRS. We perform a series of controlled experiments in natural twilight conditions (when fish predators and BRS are most likely to interact) to tease apart the different variables impacting feeding rates of potential fish predators of BRS, including interactions between prey density and substrate type.
Fish feeding experiments performed at various shrimp densities under natural twilight conditions revealed that all predators were capable of feeding on BRS without any prior exposure to the prey, but that feeding rates varied considerably from one fish predator to another (feeding rates of alewife > lake trout > goby > pumpkinseed > yellow perch). We report that young of year alewife (a planktivorous fish that utilizes Hudson River embankments as nursery habitat), and young of year lake trout (a valued, cold water predator of the Finger Lakes and Great Lakes region) are capable of feeding on BRS at extremely high rates and could act as natural biological control mechanisms to prevent further establishment of the species, regardless of substrate type. That said, feeding rate was significantly impacted by substrate type across all fish predators. In open aquaria, fish consistently ate at higher rates than if a preferred rocky substrate refuge was provided to the prey. Because BRS are also competitors for zooplankton with the same fish species that prey upon them, further research will have to tease these variables apart before any definitive conclusions can be made about the impact of BRS on fish survival and growth.