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.
(October 2004)
