The attacks happen every day all across the world. An ocean-going freighter takes on ballast water at Port A, then later discharges its tanks at Port B, injecting alien creatures from the A ecosystem into the B ecosystem. Anywhere from 7,000 to 10,000 different species may be floating in a ship’s ballast water, explains David Lodge, Notre Dame professor of biology. “
Although most of the tens of thousands of species that are transported don’t survive, the small fraction that do can be extremely troublesome,” he says. With no natural predators in the new environment, the alien creature may proliferate with devastating consequences for native species. Zebra mussels and alewives,a fish, for instance, have become nuisances in the Great Lakes.
The invasions can have serious health as well as economic consequences. “Some of these organisms are microscopic pathogens, such as cholera, and others cause red tides, threatening fisheries and human health,” John M. Drake, Lodge’s Ph.D student, notes. A 2001 cholera outbreak in Peru, which infected 530,000 people resulting in 4,700 deaths, for instance, is thought to have been caused by cholera in ballast water released in the Peruvian port.
Based on patterns of ship traffic, Lodge and Drake identified worldwide invasion hotspots and estimated rates of port-to-port invasion. Their top hotspots include Chiba, Japan; Durban, South Africa; Las Palmas de Gran Cana, Spain; Long Beach, California; Piraeus, Greece; Singapore; and Tubarao, Brazil. All are ports that have a high level of global commerce.
Shipboard treatment and filtration of ballast water before releasing it into the ocean remains the best strategy for stemming the invasion tide, the Notre Dame biologists conclude.