Ecology and Behavior of the Invasive Mysid Hemimysis Anomala in Milwaukee Harbor

Abstract

Aquatic invasive species, typically introduced in ballast water, are a concern in many ecosystems. In the Laurentian Great Lakes, the Ponto-Caspian mysid, Hemimysis anomala, has established and is especially abundant in harbor breakwall environments in Lake Michigan, forming large swarms. Predicting the effects of the invader depend on whether Hemimysis is competing for zooplanktonic prey or exploiting other benthic resources. To understand population dynamics (seasonality, size distribution, sex ratios, abundance, etc.) and food web position, weekly to monthly sampling of breakwall environments was conducted using lighted funnel traps in Milwaukee Harbor, WI. In addition to time series sampling, we also sampled from within a swarm to compare individuals in traps to individuals in the swarms. Preserved samples were quantified, body size measured, and sexes determined. In addition, subsamples of at least 6 females, males, and juveniles from each collection were stored at -70°C for gut content analysis using purified antibodies raised against potential prey species (Bosmina longirostris, Bythotrephes longimanus, Cercopagis pengoi, Daphnia mendotae, Daphnia pulex, Keratella cochlearis, Leptodiaptomus ashlandii, Limnocalanus macrurus, and veliger larvae of Dreissena mussels). Samples from mid to late summer indicate a population dominated by juveniles (