A new invasive species study by the Smithsonian Environmental Research Center (SERC) discovered one of the main tactics ships use for stopping invasive species—ballast water exchange—isn’t working nearly as well as managers hoped.

Marine scientists looked at ballast water from ships entering Chesapeake Bay before and after ballast water exchange became mandatory in 2004 and found that, contrary to expectations, concentrations of potentially invasive species have gone up, not down.

One of the big reasons they suspect is shifts in global trade, including coal exports, which could be sabotaging the effectiveness of the strategy.

Caption: SERC marine biologist Jenny Carney descends the gangway of a giant bulker ship in Virginia. When ships export coal and other goods, they return loaded with ballast water from foreign ports—and often inadvertently bring invasive species with them. (Photo Credit: Kim Holzer/Smithsonian Environmental Research Center)