New treaty fights invasive marine species.

The UN's 50-year-old shipping agency, the International Maritime Organization (IMO), has adopted a treaty aimed at combating the spread of invasive species by shipping vessels. The International Convention for the Control and Management of Ships Ballast Water & Sediments, will guide efforts to prevent the spread of waterborne species through ships' ballast water.

When a ship unloads its cargo at a port, its hull must be filled with water to maintain the vessel's stability, both in port and at sea. On arrival at a destination port, the ship then discharges this "ballast water," often introducing thousands of foreign organisms into the port's waters. For example, the Chinese mitten crab (Eriocheir sinensis) evidently traveled this way from the Yellow Sea to northern Europe, England, and the U.S. West Coast, eroding levees, clotting power plant intakes, and causing heavy economic damage wherever it lodges.

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Recent increases in global trade, spurred in part by free trade agreements, have pushed the problems associated with waterborne invasive species to a devastating level. The World Trade Organization says the volume of goods traded globally has increased by an average of six percent each year over the past fifty years.

Once ratified by 30 of the 163 IMO member states, the Ballast Water Convention will ensure that all ships built after 2009 are fitted with equipment for treating ballast water.