| Mandatory ballast water exchange (BWE) was implemented for vessels carrying ballast water into the Great Lakes in 1993; however, few data are available on its effectiveness. I conducted BWE experiments aboard six transoceanic vessels traveling from the Great Lakes to European ports. BWE was highly effective (>99% loss) for reducing concentrations of zooplankton, and for causing mortality of sentinel amphipods and oligochaetes (96-100%). BWE also dramatically reduced recruitment of zooplankton from diapausing eggs present in ballast sediment; however it did not affect egg viability when eggs were subsequently returned to freshwater. Laboratory experiments with sodium hypochlorite suggest that ships could employ this treatment to reduce the risk of invasions from diapausing eggs. Estimates of the probability of a cladoceran invasion using data from this study suggest that BWE probably provides sufficient protection for the Great Lakes as an interim measure to prevent future invasions. |
