The microbes carried in ballast water can infect plants, wildlife and even humans.
Ballast water stabilizes ships, and is discharged at ports of call and en route.
The United States receives more than 79 million metric tons of ballast water from overseas each year. It has long been known that such discharges have unintentionally spread plankton, shellfish and fish from one body of water to another, sometimes with major ecosystem impacts. But the global movement of microorganisms via ballast water discharges has been virtually ignored. Ruiz said that although there is no reported evidence of outbreaks of human diseases from non-native microbes in ballast water, the findings indicate the need for much greater concern than has been shown. Given the magnitude of ongoing transfer, and its potential consequences for ecological and disease processes, large scale movement of microorganisms by ships merits attention from both invasion biologists and epidemiologists.