Are invasives worse in freshwater than terrestrial ecosystems?

Several lines of evidence suggest that the effects of invasive species may be greater in aquatic freshwaters than in terrestrial ecosystems. We argue that freshwaters are significantly more invasible-from a number of poorly regulated sources-and also more susceptible to negative biodiversity, physical ecosystem, and socioeconomic impacts when invaded, than their terrestrial counterparts. Moreover, the nature of freshwaters appears to result in impacts that are wide ranging and severe while being indirect, diffuse, and difficult to both detect and predict. For these reasons, we conclude that freshwater invasive species represent a special case, when compared with terrestrial invasives, in which the likelihood of negative impacts, and their effects, is disproportionately severe. We suggest that future approaches to research in this area should aim to audit the full array of impacts of a number of representative invasive species, with a view to building an evidence base to support the global implementation of a precautionary approach to the release of aquatic freshwater non-native species. (C) 2014 Wiley Periodicals, Inc.