Efforts to keep ships from importing foreign species into the Chesapeake and other East Coast ports are falling short, according to a new study by the Smithsonian Environmental Research Center.

Scientists at the center, located near Edgewater, MD, found that nearly a quarter of the ballast water discharged in East Coast ports was never exchanged at sea.

Ships often take in water, along with any organisms in the water, to help stabilize their vessels before leaving port. When that water is released at its destination, it can cause the introduction of unwanted species, such as zebra mussels, which were introduced to the Great Lakes via ballast water in the 1980s.

Replacing this initial ballast water with high-salinity water in mid ocean can reduce the risk of invasions, as any species picked up there are less likely to survive when released in coastal ports, where water salinities are lower.

Since 2004, cargo vessels have been required to exchange their ballast water in the open ocean at least 200 nautical miles from land. But a team of SERC scientists analyzed 105,000 vessel reports from January 2005 through December 2007 and found that often does not happen.

While reports showed that most vessels opted not to discharge ballast water at all, many continued to release water in East Coast ports that was either never exchanged at sea, or improperly exchanged.

The study, published in the journal BioScience, found that 23 percent of the water discharged on the East and Gulf coasts was not exchanged, while that was true for only 5 percent of the ballast water released at West Coast ports.

Much of the difference stems from geography. Many of the ships arriving in East Coast ports are traveling through coastal waters and do not travel through open ocean waters where they have more of an opportunity to make the exchange.

Ecologists say the vast discrepancies point to the need for technologies that would allow ballast water treatment on board without having to journey to the open ocean. That would make every coast safer.

"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," said Whitman Miller, a SERC scientist who led the research team.

The federal government is moving toward establishing a new treatment standard for ballast water dischargers, although legislation is advancing in Congress to weaken those requirements.