Commercial ships inadvertently transfer vast numbers of living organisms beyond their evolutionary ranges, sometimes resulting in invasions of distant marine habitats. Biofouling on ship hulls translocate organisms that cling to the undersides and interstices of ships that function as hard substrate habitat for biota. Because biofouling accumulates over space and time continually, it poses risk to all ports visited. To better understand the potential magnitude of the biofouling vector in the United States, we compiled information on ship-specific dimensions as well as actual arrival histories of the fleets of ships calling at U.S. ports (2011–2014) in an effort to calculate wetted surface area (WSA) flux to the U.S. The annual mean flux of WSA from overseas bioregions to the U.S. is 333 km2 year−1. An additional 177 km2 year−1 of WSA moves among the eight distinct biogeographic regions of the lower 48 United States. We confirm that over 90% of all global marine bioregions (120 of 132 identified by IUCN) are visited by commercial ships within five port calls of arriving to the U.S. Our analysis is the first ever to quantify the extent of WSA flux among global marine bioregions and underscores the urgent need for management approaches and technologies that will reduce associated invasion risks.
