TOPICS > Science

U.S. Battles Invasive Species

July 1, 2004 at 12:00 AM EDT


JEFFREY KAYE: Hungry beetles from Asia that have destroyed trees from New York to Chicago, hyper-aggressive ants from South America that have spread across southern and western states, and a fast-growing weed from the Balkans that now infests millions of acres of California — these are some of the antagonists America faces in an ongoing struggle against invasive species. They’re the harmful plants and animals from other parts of the world that arrive and thrive in the United States, doing enormous damage in the process.

LORI WILLIAMS, National Invasive Species Council: There are invasive species all over the country of all different types. They have enormous impact. They’re considered harmful to either the economy, the environment, or in some places animal and human health.

JEFFREY KAYE: Lori Williams is executive director of the National Invasive Species Council. Composed of 23 federal agencies, the council develops policies and strategies to fight and monitor invasives. The tactics include inspecting plants at nurseries for foreign insects. Dangerous invasives, however, make up only a small fraction of all the plants and animals transplanted to the United States.

LORI WILLIAMS: There’s 50,000, an estimated 50,000 alien, or non-native, species in the country. Of those 50,000, a very small percentage, estimated very roughly around 1 percent, are considered invasive, but that’s about 500 species right there.

JEFFREY KAYE: Whether they swarm, slither, or take root, invasives are the second leading cause, after habitat loss, of native species being listed as endangered or threatened. Invasive species, such as the glassy winged sharp shooter, which spreads a disease that destroys grapevines, cost America over $138 billion a year in environmental and economic damage, according to a Cornell University study.

Take the harm done by just one species, the zebra mussel, which is native to Europe. Transplanted to the United States, it has bred and spread so rapidly that it’s crippled entire power plants in the Great Lakes and Northeast by blocking their water intake valves. How do invasive species get into the country? Often as stowaways in the cargo of arriving planes and trucks, or in the ballast water of freighter ships, which gets released when vessels come into port. Once they arrive, invasive species often face no natural predators, so they can multiply wildly. That’s what makes them so difficult to fight or control.

LORI WILLIAMS: The ecosystem has evolved without that species, so unless there happens to be a predator that takes to them right away, they have a natural advantage.

JEFFREY KAYE: One of the few places where people appear to be winning the struggle against a particularly fearsome invasive species is the Agua Hedionda Lagoon, north of San Diego. While diving here in the year 2000, marine biologist Rachel Woodfield and her colleagues discovered an intruder that was quickly turning the lagoon, home to five endangered species, into an ecological wasteland.

RACHEL WOODFIELD: You couldn’t imagine seeing something this bad. It was so obvious, the devastation that was taking place. Where we would normally expect to see this forest of sea grass filled with fish and other small animals moving about within the eel grass bed, we saw none of that. We saw this bright green plant that we’d never seen before that had spread over large areas of the lagoon.

JEFFREY KAYE: That plant was Caulerpa Taxafolia, a hearty, fast-growing seaweed native to the tropics. When introduced into predator-free waters, like this lagoon, Caulerpa runs amok.

RACHEL WOODFIELD: It just ploughs through everything in its path. It pulls down the other plants that are there. It smothers the bottom, and it forms this dense carpet on the bottom, so that when you’re down there swimming around, all you see is Caulerpa, as far as you look.

JEFFREY KAYE: Once the invader was identified as Caulerpa, local and state authorities knew that it had to be fought aggressively and quickly. They looked at what had happened in the Mediterranean, where the accidental release of a tiny amount of Caulerpa had quite literally grown into an environmental catastrophe. Thousands of acres of the Mediterranean sea floor are now carpeted in the super seaweed, and the battle against it seems lost.

In California, authorities feared Caulerpa would eventually escape from this lagoon and start destroying fisheries and underwater habitat up and down the California coast. To prevent that from happening, Woodfield and her colleagues, who work with a firm specializing in habitat restoration, were given a mission by local and state environmental officials: Destroy every bit of Caulerpa in this body of water without destroying the lagoon itself.

RACHEL WOODFIELD: Because it’s so easy to spread, we decided the best way to approach it would be to treat it right where it is.

JEFFREY KAYE: They first covered the Caulerpa fields in giant plastic tarps, sealing the seaweed off from surrounding areas. They then applied poison.

RACHEL WOODFIELD: We put liquid chlorine. We pumped it underneath the tarps, and that will immediately kills everything in the water, but the tarp is there to hold it on so it only kills what’s under the tarp, not the lagoon water at large.

JEFFREY KAYE: The scientists are now surveying every square inch of the lagoon floor to see whether their Caulerpa-killing strategy is working and whether native species are returning in healthy numbers. They’re also comparing places where they’ve eradicated Caulerpa to other selected areas of the lagoon.

ROBERT MOONEY: Essentially, what we’ll do is we’re doing control sites that we’ve monitored before and after eradication. And so once the community and area where we’ve removed the Caulerpa looks like the control sites, then we know that, you know, a normal native community has reestablished and we’ve been successful in both protecting the lagoon and of getting rid of Caulerpa.

JEFFREY KAYE: Although the eradication effort here is going well, Woodfield isn’t letting her guard down.

RACHEL WOODFIELD: We believe we need to find every single piece. If we leave a little piece behind by quitting early, we run the risk of throwing away all this time and money that we have spent so far.

JEFFREY KAYE: That’s why constant vigilance after eradication, like the kind occurring at this lagoon, is so necessary, if the fight against invasive species is to be successful, says Williams.

LORI WILLIAMS: You can eradicate, but you really have to have a long-term effort to do it, and you’ve got to have the follow-up or your eradication is not going to be successful and the species will reestablish.

JEFFREY KAYE: As invasive species arrive in the United States at an ever-faster rate, many scientists and environmentalists are urging the Bush administration to take more aggressive action. They want to see better screening of imported goods and more federal funds to detect and respond to the problem. They’re also seeking passage of the National Aquatic Invasive Species act, which would expand and tighten regulations controlling the discharge of ballast water from cargo ships in American ports. Williams acknowledges that tough economic choices have to be made if the fight against invasive species is to be effective.

LORI WILLIAMS: We can’t keep everything out and we’re not going to stop trade, but it’s worth considering the impacts of these species, taking the time to evaluate them and making sure that it’s worth the risk to bring in some of these products or just change the way we bring them in by addressing the pathway.

JEFFREY KAYE: But as the world continues to shrink, thanks to increased trade and travel, those involved in the struggle against invasive species are fatalistic, knowing the arrival of new adversaries is inevitable.