The Potential for Intracoastal Transfer of Non-indigenous Species in the Ballast Water of Ships

A principal mechanism for the transfer of non-indigenous species among aquatic ecosystems has been through the movement of ships’ ballast water. To date, most ballast water studies have focused on the transoceanic movement of organisms while ignoring the potential for spread by intracoastal traffic. This study measured the transfer of estuarine and coastal species by domestic ship traffic between Somerset, Massachusetts and Norfolk, Virginia, U.S.A. Plankton diversity and abundance in the ballast water of a coal carrier at the beginning and end of seven replicate voyages were estimated. These data, collected over a 1-year period, were used to (1) characterize plankton assemblages in the ballast water, (2) assess survivorship of ballasted organisms for the voyages by comparing initial and final abundances, and (3) test for differences in survival as a function of voyage or taxonomic group. A diverse assemblage of organisms was transported intracoastally that was dominated by dinoflagellates, diatoms and copepods. In four of seven voyages, total abundance declined significantly over the 36-h journey; however, considerable within- and among-voyage variation in numerical response among major taxonomic groups was observed. Despite a general decline in abundance, millions of organisms nevertheless survived each voyage and were released into the receiving harbor. These data indicate that ballast water carried by domestic ships is potentially an important vector for transferring aquatic non-indigenous and native nuisance species. Thus, future management decisions concerning ballast water transport should consider the role of domestic traffic in promoting invasions.