A ranking scheme for high-impact non-native aquatic invaders

The current lack of tools for assessing the impacts of nonnative aquatic invaders is a serious technological gap that strongly affects the screening capability of federal and state agencies for potential invasive nonnative invaders. Impact assessments have been made for nonnative, invasive plants by various NGOs and agencies.  However, no comprehensive impact assessment system exists for nonnative aquatic invaders in the US, despite the massive economic and ecological harm caused by these species.  We quantify impacts of nonindigenous aquatic invaders, using a series of point-based questions designed to elucidate ecological as well as socioecomic and human health impacts.  Additionally, we quantify the likelihood of spread, given the current and potential distribution as well as the dispersal and colonization potential.  We suggest a modified version of NatureServe’s methods for nonnative plant impact ranking.  Environmental managers can use these questions and the resulting impact scores to assess which aquatic species are causing or likely to cause the high impacts, providing an approach to direct management efforts towards high-impact species.  Available evidence indicates that those species that cause harm in one region often have high impacts in other regions.  Enhancing availability of regional lists of both high-impact and low-impact nonnative aquatic species will aid those who screen incoming cargo so that they can focus on nonnative species that have caused high impacts in other parts of the world.  Thus, the implementation of this system will aid the worldwide effort against the introduction of nonnative aquatic species.