The horror stories are becoming all too common: kudzu covering every tree, power line, and telephone pole from roadside to mountaintop, throngs of Chinese mitten crabs clogging California aqueducts, nutria (large rodents native to South America) devouring marshland vegetation across the Chesapeake Bay, leaving little habitat for native oysters. Invasive species are on the march.
When plants, animals, and other organisms are moved from one area to another—deliberately or accidentally—the result is often bad news. A 1999 report by Cornell University researchers estimates the economic cost of invasive species at $138 billion annually. In addition, they estimate that introduced species pose potential trouble to nearly half of all federally listed threatened and endangered species.
“Populations of newly introduced species can expand so rapidly that they knock natural systems out of equilibrium. That can be costly to people. Invasive species are equivalent to an ecological tax that we all have to pay,” says Michael Blum, a molecular biologist with the U.S. Environmental Protection Agency (EPA).
Blum is searching for high-tech ways to stem the tide of invasive species. He and his colleagues at EPA’s Molecular Ecology Research Branch in Cincinnati are developing ways to use DNA-based techniques to screen for potentially troublesome exotics in ballast water, the water that large, ocean-going ships regularly pump in and out of storage tanks to maintain stable buoyancy.
A single liter of ballast water might contain dozens of different species and thousands of organisms. Since the great majority of those can be larvae, a ship releasing ballast into U.S. waters is like blowing 10,000 ripe dandelion (another introduced species) seeds across your newly-seeded lawn.
Blum wants to know what organisms might be lurking in that liter of water. To do so, he begins by separating the living organisms from the water, then concentrating the tissue to extract the DNA and get a representative sample of the genetic material in the ballast water. Sequencing from the DNA then yields genetic “bar codes” Blum examines to learn what species were in the ballast water, perhaps transported from far-off ports of call by the traveling ship.
Because this is the first use of DNA bar-coding in response to the threat of aquatic invasive species, Blum is also carefully documenting and cataloging what he finds, creating a reference library of DNA barcodes for both native and exotic species in the Great Lakes. This will help the Coast Guard and other resource managers track—and hopefully stop—invasive species introductions in the future.