First records and distribution of the invasive amphipod Echinogammarus ischnus (Stebbing, 1899) in the Illinois Waterway, USA

The spread of non-native and potentially invasive species is a global issue that is widely regarded as one of the major threats to native biodiversity. Non-native, aquatic macroinvertebrates can be particularly challenging to study because they can spread undetected across large geographical barriers, and species identification of small, cryptic macroinvertebrates is labor intensive and can require considerable taxonomic expertise. The Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing, 1899) has expanded its non-native range in North America, now including the Great Lakes and several large interior rivers within the United States. Here we report the first comprehensive assessment of the amphipod E. ischnus in the Illinois Waterway, which connects Lake Michigan and the Great Lakes Basin to the Mississippi River Basin. Based on colonization samplers (i.e., rock bags) deployed at 370 sites along the Illinois Waterway, E. ischnus currently exists in low abundance and has a disjunct distribution across the Illinois Waterway. Sites where E. ischnus was captured were strongly associated with high-activity commercial shipping areas. This observed association with commercial shipping areas should guide early detection efforts for E. ischnus in other industrialized waterways.