Exotic species in the Hudson River Basin: A history of invasions and introductions

We compiled information about the distribution of exotic organisms in the fresh waters of the Hudson River basin. At least 113 nonindigenous species of vertebrates, vascular plants, and large invertebrates have established populations in the basin. Too little was known about the past or present distributions of algae and most small invertebrates to identify exotic species in these group. Most established exotic species in the Hudson River basin originated from Eurasia or the Mississippi-Great Lakes basins, and were associated with vectors such as unintentional releases (especially escapes from cultivation), shipping activities (especially solid ballast or ballast water), canals, or intentional releases. Rates of species invasions of fresh and oligohaline waters in the basin have been high (ca. one new species per year) since about 1840. For many well-studied groups, introduced species constitute 4% to nearly 60% of the species now in the basin. Although the ecological impacts of the invaders in the Hudson River basin have not been well studied, we believe that about 10% of the exotic species have had major ecological impacts in the basin. Since the rates of entry and composition of exotic species in the Hudson basin are similar to those observed previously for the Laurentian Great Lakes, invasions tended to occur earlier in the Hudson basin, probably reflecting the earlier history of human commerce. While most exotics have had negative impacts on local flora and fauna, some fish species have provided unique angling opportunities and important economic benifits.