Overview of biological invasions in the Chesapeake Bay Region: Summary of impacts on native biota

Human activities have resulted in the transfer and establishment of thousands of species of organisms outside their natural range. Although the rate of these biological invasions appears to be increasing in estuaries worldwide, the ecological impact of invasions on biodiversity in the Chesapeake Bay is poorly known. Using an intensive analysis of literature, we evaluated the impacts reported for 202 species of known, probable, or possible introductions (cryptogenic) to the Chesapeake Bay, including members of 17 phyla. Thirty-eight nonindigenous or cryptogenic species were considered to have probable impacts on native biota, but only 12 (34%) of these species have quantitative data available on their impacts. Furthermore, of the 38 species, 21 appear to have potentially threatening or serious impacts. Seven species appear to pose widespread threats to native species; and at least 14 more are believed to have serious local effects on native species or ecosystems. However, even among the 21 species with potentially serious or threatening impacts, quantitative data were available for only 8 of those species. The poor quality of existing information poses a significant problem for management of introduced species, since efficient management must evaluate trade-offs between impacts of exotic species and the cost and environmental disturbance associated with control methods.