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Public Radio's Environmental News Magazine (follow us on Google News)

Combating Bio-Invaders

Air Date: Week of

Many American harbors are polluted with invasive organisms, often transported in the ballast water of ships. The problem is particularly bad in California. But, scientists there are developing aggressive ways to combat invasive species. Nathan Johnson reports.


CURWOOD: This is Living on Earth. I'm Steve Curwood. The world is full of plants and animals that evolved in one place, but that people have transferred somewhere else. We take many of these non-native species for granted. The horse, for instance, or wheat, even honey bees. But for every transplanted species we find useful, there are thousands we consider pests. They crowd out native species and threaten crops and fisheries. The problem is especially acute along the coast of California. Now, scientists there are launching some unique counter-measures against marine bio-invaders. Nathan Johnson reports.

(Splashing water)

JOHNSON: San Francisco has long been one of the busiest harbors on the West Coast. Scores of ships arrive every month from exotic places, many of them carrying exotic species in the ballast water that ships take on for stability. Because this is such a busy crossroads, San Francisco Bay has become the most heavily-invaded aquatic ecosystem in North America. A new exotic species shows up every three months.

COHEN: It's completely altered, the Bay Area ecosystem. Across most of the habitats the impact is so large, it's almost hard to see it's so big. And so, as we spend time out in the bay, we find that virtually everywhere we look are exotic species, and they dominate the ecosystem.


JOHNSON: Scientist Andy Cohen of the San Francisco Estuary Institute has been tracking the impact of bio-invaders on inter-tidal mud flats.


JOHNSON: Wearing rugged wading boots, he's crouching over a sieve like an old prospector panning for gold, trying to get a look at what's living in the mud.

(Sound of panning, shuffling of shells)

COHEN: We've scooped up some mud into this sieve and we're shaking it down. (Shakes) Here's our clam life. One very colorful Japanese little-neck clam. A lot of them are the Atlantic gem clam; these are eastern soft-shell clams. These are longer and narrower ones.

JOHNSON: Nothing really native in that.

COHEN: Nothing native in that batch at all.

JOHNSON: Exotic species like these have robbed the bay of its unique biological identity. Foreign clams, for instance, have flourished so dramatically they're stripping the ecosystem of nutrients. Dr. Cohen says this is rippling up the food chain.

COHEN: Because of the filtering of water that this clam is doing, the entire food web relations, what we refer to as the trophic structure of the ecosystem, had been changed virtually overnight. It's just remarkable. And yet, that happens with invasions. Not all invasions, but it is not a rare phenomenon.

JOHNSON: Besides disturbing millions of years of evolution, exotic invasions are inflicting costly damage. Commercial shell fisheries along the entire Pacific coast are currently under assault by European green crabs, which love to eat clams and oysters. Invasive species are such a problem that some California scientists have begun to launch an aggressive counter-attack.

(Echoes, running water, door opening)

KURIS: So this is the quarantine area where we keep the non-native crabs. They have to remain in this room at all times.

JOHNSON: Armand Kuris is a professor of marine science. From his lab at the University of California in Santa Barbara, he is leading an effort to fight back.

KURIS: My view is we, in fact, can't learn to live with some of these things. They are serious pests. I am seeking to control or eradicate them.

JOHNSON: People have tried all sorts of ways to stop the spread of non-native plants and animals, from poisoning lakes to get rid of unwanted fish, to using insects to control weeds. The ocean, though, is a more complicated ecosystem, and many scientists feel that marine invaders are nearly impossible to effectively control. But not Professor Kuris.

KURIS: Our lab, and a few other labs, an important lab in France, an important lab in Australia, have started ending the fatalism, ending the defeatism, and saying can we take a proactive stance? Can we actually go after these things and reduce or completely alleviate the impact, the negative impact of them?

JOHNSON: Dr. Kuris is the first to actually eradicate an exotic marine pest: a tiny South African sea worm called the sabellid , which was infecting a California abalone farm. To do this in 1997, he sent a small army of volunteers to the shallow waters surrounding the farm, to remove all the snails and clams that the worms were using as hosts. It was a scorched-earth tactic that worked.

KURIS: Against this sabellid worm that infested abalone and other snail shells, we were able to eradicate a population that was two-and-a-half million worms out, established in California. That means that you can manage a pest. We have the ability.

JOHNSON: Now Dr. Kuris is looking to combat the European green crab in San Francisco Bay and the west coast, with an equally aggressive approach. He wants to introduce a European parasite that will prevent the crabs from reproducing. The technique is known as biological control.

KURIS: The kinds of parasites that have biological control potential are firstly a very strange group of organisms called parasitic castrators. Strange creatures, parasitic barnacles that invade the tissues of the crab, come to weigh 20 to 30 percent of the weight of the crab, and completely block reproduction.

(Glass aquarium lids sliding open)

JOHNSON: Dr. Kuris and his research assistant are currently testing the parasitic larvae, called cyprid, in their special quarantine lab. The biggest question is whether the cyprid parasite will target only the European green crabs, or will it infect other, native crab species in California?

KURIS: So in this container, we have the native test crab. What we're doing is exposing these to the cyprid larvae, the infective stage, and we'll dissect them to determine if these crabs are infected.

JOHNSON: So far there is no proof the parasite will attack only the exotic crabs that Dr. Kuris wants to kill, which leaves some researchers extremely wary of his project.

(Sounds of San Francisco Bay)

JOHNSON: Back in San Francisco Bay, scientist Andy Cohen fears a disaster could result if European parasites are brought in to combat European crabs.

COHEN: Fundamentally, what we're talking about is introducing yet another exotic species into the ecosystem. It is difficult, if not impossible, to predict exactly how an organism will behave, how it will respond in a novel environment, and so with every introduction into an ecosystem we are taking a certain risk.

JOHNSON: In fact, early attempts at biological control were catastrophes. The mongoose was released in Hawaii to control rats in the late 1800s. And in the 1930s, the cane toad was introduced in Australia to control beetles. Both species began to devour native animals instead. Dr. Kuris says scientists have learned from these mistakes. However, he'll likely face stiff opposition to introducing exotic parasites in San Francisco to control invasive crabs. Meantime, as his research continues, other people are taking steps to ensure the invasive species problem won't get any worse.

(Ship horn, bell, radio and loud noise from Port of Oakland)

JOHNSON: At the Port of Oakland, crews are busy using cranes to load container ships with cargo.

(Voice of radio communication among crane operator and crew)

JOHNSON: As they're loaded, these ships dump tens of thousands of gallons of ballast water into the port. In the past this water was brimming with exotic marine organisms from Europe or Asia or wherever the ship came from. But now, Oakland requires ships to clean up their ballast before entering the harbor.


ZAITLIN: The port has instituted its own ballast water regulation, which requires ships that call here from foreign ports to exchange their ballast water at sea.

JOHNSON: Jody Zaitlin is the port's environmental planner. She says when a ship exchanges its ballast water on the high seas, the most dangerous biological stowaways are flushed away.

ZAITLIN: What they're picking up and using as ballast is open ocean water, which has a much lower density of organisms, and the organisms that are in the open ocean are much less likely to survive once they're discharged in near-shore environments like the bay.

(Bells ring)

JOHNSON: Next year, ships entering all California ports will be required to exchange their ballast at sea. And the Coast Guard has asked ships nationwide to voluntarily follow California's example. Still, environmentalists say ballast exchange is not 100 percent effective. They say the best solution is to treat ballast water on shore, at a processing plant, the same way sewage is treated. The shipping industry is resisting that step, saying it's too costly. Instead, Ms. Zaitlin says technicians are investigating ways of disinfecting ballast water inside the ship itself.

ZAITLIN: There are a couple methods under investigation for on-board treatment, such as chlorination, UV light, UV light plus filtration, heat treatment, ozonation, a number of other water quality techniques.

JOHNSON: So far, though, none of these technologies are currently available. Maritime commerce is expected to double in the U.S. in the next 20 years, and this explosive growth in global trade has many environmentalists worried the invasive species problem will grow as well. They say the ballast exchange program is a good first step, but they vow to continue their fight for more effective ballast treatment.


JOHNSON: For Living on Earth, I'm Nathan Johnson in Oakland.



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