Much of the problem comes down to simple geography. Depending on a ship's transit route, it may not have the time or space to conduct open-ocean exchange.
A mere 24 percent of the ballast water discharged by ships journeying to U.S. ports along coastal routes, from Central or South America, for example, underwent open-ocean exchange. In contrast 91 percent of ballast water discharge by transoceanic shipping was exchanged in the open ocean, where ships have more opportunities to manage their water properly.
Because so many of their incoming ships do not pass through the open ocean, ports in the Gulf and East Coast receive more potentially harmful water.
The vast discrepancies point to the need for another solution, ecologists say. If ships could treat their ballast water on board without having to journey to the open ocean, every coast would be safer.
"The Gulf of Mexico coast receives more overseas ballast water discharge than the East or West coasts, and most of this water is either unexchanged or exchanged inside coastal waters," Miller said. "Given the geographic constraints of shipping, and the complexity of the invasion process, it is clear that we need to move to onboard ballast water treatment technologies that will allow ships to operate anywhere in the world without fear of releasing harmful invasive species."
|Contact: Kristen Minogue|