Ecological and Economic Impacts of Aliens in the Hudson

We cannot make a rigorous accounting of the effects of alien species in the Hudson because (1) we don't have a full list of aliens in the river; (2) fewer than 10 percent of known aliens in the Hudson have received serious study; and (3) there has been no attempt to investigate the interactions among alien species, or between species introductions and other human impacts on the ecosystem. Nevertheless, the effects of alien species in the Hudson ecosystem surely are large and pervasive. Alien species have altered water chemistry, flow, and clarity, and biogeochemical cycling. They have become important predators, prey, and competitors of the native biota, thereby changing the complexion of biological communities throughout the estuary. Alien species have become valuable parts of the fishery, but interfered with boating and swimming and intake of drinking and cooling water. They have affected the ecology of the main channel, the shallows, rocky shorelines, and wetlands, and have presumably affected the brackish and marine sections of the estuary as well as the freshwater estuary. There probably is no habitat, general ecological process, or important human use of the river that has not been significantly changed by alien species. Introduction of alien species is one of the most important ways that humans have affected the Hudson River ecosystem.

The impacts of alien species on the Hudson seem certain to increase in the future as new invaders establish themselves in the river. Mills et al. (1996) estimated that about 15 percent of the aliens in the freshwater part of the Hudson basin have strong ecological effects, and current invasion rate is about seven species per decade. This suggests that we might see a new, ecologically important alien about once a decade in the freshwater part of the basin, in addition to new arrivals in the lower estuary. Alien species with strong ecological effects that probably will appear in the Hudson in the next five to fifty years include Corophium curvispinum,a filter-feeding am-phipod that is spreading through Europe fouling pipes and crowding out other benthic animals, including the zebra mussel (!) (van den Brink, van der Velde, and bij de Vaate, 1993; Paffen et al., 1994); Echinogammarus ischnus, another Caspian amphipod that already is widespread in the Great Lakes, where it is displacing native amphipods (Dermott et al., 1998); the New Zealand mud-snail Potamopyrgus antipodarum, established in the Great Lakes and elsewhere in North America, Australia, and Europe, where it has strong ecological effects (Hall, Tank, and Dybdahl, 2003); the Chinese mitten crab Eriocheir sinensis, now established on the West Coast (Cohen and Carlton, 1997) as well as in Europe, a species that migrates hundreds of kilometer into fresh waters and destroys dikes and river banks with its extensive burrows; and the round goby Neogobius melanostomus, a benthic fish that is now extremely abundant along Great Lakes shorelines (Charlebois et al., 1997). As these and other species appear in the Hudson, the cumulative impacts of alien species will increase.

As is apparent from the case studies, eradication or comprehensive control of alien species is rarely attempted and usually unsuccessful. Aside from local control programs (for example, cutting water chestnut near marinas, poisoning zebra mussels in water intakes), only the water chestnut and purple loosestrife (Malecki et al., 1993) have been the objects of serious eradication programs in the Hudson. Whether the impacts of aliens are desirable or undesirable, they usually are irreversible.

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