Human-mediated transfer and invasions of organisms have permanently altered distribution patterns on a global scale. In response to growing numbers and impacts of invasions, global-scale vector management is advancing to curtail unintentional and unwanted species re-distributions. In marine systems, ocean-going ships have been the major dispersal mechanism across biogeographic barriers, and maritime vector management has become a priority global initiative, including national regulations and recent ratification of an international convention to manage ballast water. This paper provides the first analysis of the pioneering patterns of ballast water treatment systems (BWTS) on board commercial ships, using vessel arrivals to the United States as a model system. Over an opening 28-month period, >200 unique vessels arriving to the U.S. reported BWTS operations, using 58 different systems to treat 4.42 million m3 of discharged ballast water. Although this volume represents <2% of all ballast water discharged in the U.S. per month during this period, there was substantial growth in treated ballast discharge throughout this time. Through 2015, ‘Filtration UV’ systems were the most common BWTS type installed across all ship types. Currently, BWTSs occur on higher numbers of tankers and bulkers, but a higher proportion of passenger vessels, than other ship types. If BWTSs meet the required discharge standards as intended, this will cause a steep reduction in total discharge of organisms ≥50 µm compared to current practices. While several hurdles in fleet-wide BWTS adoption remain, including the timeline for BWTS installation across the global fleet, we are at a significant milestone in the history and evolution of global shipping, which is undergoing wholesale transition to a new and more effective global-scale ballast vector management strategy.
