EXOTIC SPECIES IN THE HUDSON RIVER BASIN - A HISTORY OF INVASIONS ANDINTRODUCTIONS

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 speci es in the Hudson River basin originated from Eurasia or the Mississipp i-Great Lakes basins, and were associated with vectors such as uninten tional releases (especially escapes from cultivation), shipping activi ties (especially solid ballast or ballast water), canals, or intention al releases. Rates of species invasions of fresh and oligohaline water s in the basin have been high (ca. one new species per year) since abo ut 1840. For many well-studied groups, introduced species constitute 4 % to nearly 60% of the species now in the basin. Although the ecologic al impacts of the invaders in the Hudson River basin have not been wel l studied, we believe that about 10% of the exotic species have had ma jor ecological impacts in the basin. Since the rates of entry and comp osition of exotic species in the Hudson basin are similar to those obs erved previously for the Laurentian Great Lakes, invasions tended to o ccur earlier in the Hudson basin, probably reflecting the earlier hist ory 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.