Historical trends of aquatic invasive species introduction and establishment in Illinois, USA

Tracking the introduction and establishment of aquatic invasive species (AIS) is important for monitoring the biological and economic health of freshwater environments. The state of Illinois (USA) is a critical region for understanding the threats of AIS because it possesses the only continuous aquatic habitat connecting the Laurentian Great Lakes and Mississippi River Basins. In this study, we update a previous effort to catalogue and evaluate historical AIS records from Illinois. Our updated database shows that there are now at least 92 nonindigenous aquatic species established in Illinois and a further 51 have been recorded as introduced but not established. This is more species than reported in the earlier database, most likely due to improved access to data and a longer timeframe of analysis. Rates of introduction and establishment have continued to increase in Illinois over the past century, and we identify new groups of organisms that were not in the previous database. Current sampling efforts are not sufficient to detect the number of invaders present and additional non-native species may be present but not yet recorded. Illinois is likely to remain an important hub for the introduction and spread of invasive aquatic species with implications for freshwater ecosystems across the continent.