Freshwater hotspots of biological invasion are a function of species–pathway interactions
The introduction and spread of aquatic invasive species constitutes a global epidemic that continues to homogenize the world’s aquatic flora and fauna. Species invasions are occurring at an unprecedented scale, yet few centrally organized distributional databases can accurately display location information used to prioritize management efforts within a watershed, region, or political boundary. For particularly harmful groups of invaders such as some freshwater invertebrates, one consequence is that predictive power is limited because current invasion patterns are unknown. We used the Nonindigenous Aquatic Species database of the US Geological Survey to determine current hotspots of invertebrate invasion in the US and compared those patterns with better-documented fish invasions. Invasive freshwater invertebrates were densely clustered in the Laurentian Great Lakes region compared to invasive fish that were concentrated in Florida and the Southwest. However, temporal patterns of fish and invertebrate invasions did not significantly differ. Ballast water was the most important source of invertebrate introductions, whereas fish were more often introduced by stocking, aquaculture, and aquarium release. A centralized database of current species distributions, ideally at the global scale, would greatly inform prevention and mitigation efforts for harmful species invasions.