January 30, 2002
Nutria. The word is so close to "nutritious" that you might think it refers to one of those meal-in-a-can products like Sustacal. But if you've spent time in southern Louisiana, you probably know that nutria are large semi-aquatic rodents that have overrun the state's wetlands. They look like giant guinea pigs sporting long rat tails, with the added delight of oversized orange teeth. You might have seen them in the zoo, in a bayou or a drainage canal, on a restaurant menu or, most likely, as roadkill. Maybe you even ordered the nutria gumbo, though efforts to win the public over to the idea of nutria as a tasty treat have not been overly successful.
The impetus for marketing nutria as food is not to bolster Louisiana's reputation for eccentricity, but to encourage the hunting and trapping of the animals. They might look harmless--some people even think they're cute--but they are a textbook example of an invasive species. Nutria have made a home for themselves in 22 states--even as they're disappearing from some of their original habitats in South America.
The Maryland tidewater has the nation's second-worst nutria problem, but in Louisiana they've taken over the landscape to an unprecedented degree. They greatly exacerbate the plight of Louisiana's disappearing coastline by eating the roots of the marsh grasses that hold the wetlands together. When the roots are gone, the soil washes away.
Lauren Nolfo, a doctoral student of ecology and evolutionary biology, has the nutria itch--figuratively speaking. She's passionate about her work with the animals despite a literal bout of nutria itch, a rash caused by a parasite transmitted by nutria excrement in the water. "They're fascinating animals," she says. "I love talking about them."
She revels in the grotesque details--their nipples are on their backs, their yellow-orange teeth are razor sharp, they seem to be immune to strychnine poisoning, and like all rodents they continue to grow over the course of their lifetime. Nolfo is working with a U.S. Geological Survey project in Jean Lafitte National Park to document nutria impacts at different densities. Researchers will catch and enclose nutria in a fixed area in order to see how quickly a given number of animals can decimate the environment. This will allow them to develop a computer model that will help the park do a better job of keeping populations under control.
Nolfo is also beginning her own study of nutria and their parasites. "I'm curious to see if the parasites they harbor are from here or whether they brought them from South America," she said. "If they did bring foreign parasites, I want to know if they're affecting muskrats. Muskrat populations have plummeted even though they're not directly competing with the nutria for food." Nutria were brought to the United States around the turn of the century for use in fur farming.
The McIlhenny family of Tabasco sauce fame brought some of the animals to Avery Island. Legend has it that Louisiana's horde of nutria are the descendants of some McIlhenny nutria that escaped during a hurricane. That's an oversimplification--nutria were probably released in Louisiana before that incident and were definitely released afterward, either by accident, by frustrated fur farmers who weren't making a profit, or deliberately in an attempt to control water hyacinth. But nutria are such tireless and prolific breeders, with alligators as their only local predator, that just a few escaped animals would have been enough to give us the problem we have today.
"They can reproduce year-round, they have five or six offspring per litter, and the babies are really precocious," explained Nolfo. "They're born covered with fur, with their eyes open, and within 24 hours they can eat solid food and survive." And yet, as destructive as nutria are, they are only the most photogenic of a slew of invasive species that threaten the fragile state of Louisiana.
Louisiana is at first glance almost unrecognizable in a map designed by Rich Campanella. It doesn't have the familiar "L" shape. Instead, the state is viewed from an oblique angle so that the fraying, delicate wetlands and maze of navigable waterways of south Louisiana fill up the foreground. Campanella chose this perspective because it emphasizes what makes Louisiana particularly vulnerable to introduced species.
Campanella is assistant director for environmental analysis at the Tulane-Xavier Center for Bioenvironmental Research, which has been working to develop a comprehensive approach to dealing with introduced species in Louisiana. Their work has recently received a boost with a grant from the Coypu Foundation, which administers funds set aside for conservation and environmental concerns by an heir to the McIlhenny estate. Coypu is the French word for nutria. Campanella's map is part of that project.
"One of the things we wanted to do was to produce a tangible, lasting product that people could refer to as a synopsis of the issue of invasive species in Louisiana--the concern, the species, the pathways, the impacts and the solutions," he said. The state is the crossroads where middle America meets the Gulf, the Caribbean, and all that lies beyond. New Orleans is the third-largest port in the nation in terms of tonnage. But if all the mini-ports throughout south Louisiana are taken together, they constitute the country's largest port, even without adding New Orleans to the picture. The ports draw species in; the wetlands, mild climate and rich soil provide a setting where many can thrive.
"Louisiana is a hot spot for species introduction," Campanella said. "It's the perfect environment for species from other places to arrive, thrive and spread." There are more than 900 species in Louisiana that are not native to the state. That includes plants, animals, insects, even viruses. The majority of them are harmless or even beneficial. Sugarcane and cotton, our most important crops, are introduced species. So are azaleas and crepe myrtles. But other species wreak havoc on the landscape. Of course, most people who live in the United States could be considered a self-introduced species and some might say an invasive one. It is human industry that allows species to spread.
Non-native pests arrived in Louisiana almost as soon as non-native humans did. The mosquito species Aedes aegypti came to New Orleans from Africa, probably via water stored on slave ships. The insects carried the virus that causes yellow fever, which devastated the region in the 19th century. Although yellow fever has been eradicated in New Orleans, Aedes aegypti are still with us. Scores of new invasive species arrived in the 20th century.
Formosan termites don't spread disease, but they are terribly destructive to New Orleans in their own way. These "super termites" entered the United States on shipping pallets from East Asia during World War II. They are voracious eaters that can spread by serially infesting one railroad tie after another, and do millions of dollars' worth of damage to New Orleans' historic architecture and live oak trees every year. Out in the Gulf of Mexico, the giant Australian Spotted Jellyfish are appearing in large masses that may upset the shrimp industry.
Hydrilla, water hyacinth and salvinia are clogging the state's bayous. The CBR's map depicts Louisiana's major invasive species, how they got in, and how they spread via a variety of pathways. Shipping, trucking and railroads between ports, for example, mean that whatever shows up in Houston or Mobile will likely make its way to New Orleans. Formosan termites and Asian Tiger mosquitoes probably arrived in Houston first. Fire ants and cogan grass first showed up in Mobile. Species can spread through waterways without the help of a ship.
The zebra mussel, which is choking the Great Lakes, has made its way down the Mississippi River to Louisiana. When oil rigs are moved from one location to another, they may bring species with them. Giant Salvinia, a Brazilian aquatic fern, has been spread throughout southwest Louisiana by boating and fishing equipment moved from one lake or bayou to another. Water picked up in one location and dumped in another can also spread non-native species. This happens on a large scale with the ballast water carried by oceangoing vessels, which brought the zebra mussel to America, and on a small scale with bait buckets.
Native animals can help disperse a new species. Birds, for example, have spread the invasive West Nile virus throughout the United States. On a smaller scale, they may have played a role in the spread of salvinia. When large expanses of land are planted with a single crop, foreign parasites can spread. That's how the boll weevil traveled from Mexico into the American South. Pathways for new species can open up when native species disappear and when local ecosystems are disturbed. As wolves have disappeared, coyotes have spread to take their place.
Even when we try to repair environmental damage, we can inadvertently help invasive species spread. Researchers at the CBR are concerned that freshwater diversion projects designed to help preserve wetlands could also carry zebra mussels and rainbow smelt into new areas. And increased globalization will likely mean increased introduction of non-native species and the possibility of a "global McEcosystem." Newly arrived in America is the West Nile virus. It might seem odd to think of viruses as introduced species, but they are often illustrative examples of how organisms spread in an increasingly interconnected world.
West Nile virus arrived in New York in 1999 and made its first appearance in Louisiana in 2001. "There are different possibilities as far as how it got to New York," explained Dawn Wesson, associate professor of tropical medicine and Tulane's resident mosquito expert. "It could have come in an infected vertebrate host that wasn't showing symptoms. A lot of frogs and other animals are imported for use in medical schools or laboratories that don't go through the same quarantine procedures a dog or horse might go through. It's possible that an illegally imported animal, a parrot for example, could have become infected.
An infected mosquito might somehow have survived a plane ride. Some people have mentioned bioterrorism, but it's not a very good weapon because it moves pretty slowly and depends on local conditions." West Nile is usually spread from mosquitoes to birds and back again. Birds carry it into new territory. Humans can become infected when bitten by an infected mosquito. Fear of contracting West Nile is probably overblown--only a small minority of those who are exposed to the virus develop symptoms, and only a small number of Americans have died from the disease. But that doesn't mean we shouldn't be concerned.
"West Nile, like most emerging disease problems, is of our own making," Wesson said. "They're not occurring as part of the natural process. This is about our modern way of life." And despite quarantine laws and other safeguards, it's probably impossible to keep such things from spreading. If a virus is identified early enough, it may be possible to eradicate it. "Some people say that if the mosquito-control response had been very rigorous when they first discovered West Nile in New York, it could have been eradicated. I'm not sure if that's true. But at this point this virus is here to stay," Wesson said.
So the issue becomes one of controlling the virus and preventing it from spreading to humans. Wesson's lab is working on identifying which species of mosquitoes are most likely to spread the disease so that control efforts can be focused most effectively. No matter what you do, different species are going to be coming in," said John McLachlan, director of the CBR. "You can't stop it. So we have to come up with a long-term strategy where we can monitor what's coming in, predict where it's going to go, and intervene ahead of time."
The upside to living and working in a hot spot for invasive species is that there's a natural laboratory right outside the door. McLachlan mentioned a recent incident when an oil rig was brought into the Gulf of Mexico from somewhere off the coast of Africa, bringing an entire coral reef ecosystem with it. "The most effective way to deal with something like that is to see what's there, then get in contact with naturalists and biologists in the country of origin to find out about these different species," McLachlan said. "We can find out what salinity they need, what current, what kind of food. Then we can figure out whether it's going to survive and where it might start to colonize. If it's going to be a threat, we can get ahead of it and keep it from habitating where it seems to be habitating."
Building on Campanella's map, they want to create a mapping system that will model how species may spread. They also have been working with members of Tulane's Department of Tropical Medicine to use some of the methods used to track the spread of AIDS to follow how species enter the United States. "We want to use the thinking and technology that are only available at big universities where you can tap into the expertise of people in economics, biology, information systems, public health and engineering to start to make sense of a very complex situation," McLachlan said.
"I like to do big science that requires people of different expertise to work together collaboratively and do something in a way that's never been done before. We want to bring a new approach to what is a growing problem in the United States and in New Orleans in particular."
They want to bring that new thinking not only to the species that are on their way, but also to dealing with what's already here. For example, the CBR has an ongoing collaboration with the U.S. Department of Agriculture laboratory in New Orleans to use the CBR's research on hormones to block or accelerate the metamorphosis of the insects in order to inhibit their ability to reproduce. "Eventually, this should lead to a method to treat wood with natural compounds that would interfere with the insects' hormones," McLachlan said.
CBR researchers have also been talking to their colleagues at the Audubon Institute's Species Survival Center about ways to cut down the reproductive ability of nutria. "They're experts in assisted reproduction for wildlife, in how to fertilize wildlife eggs and carry them to term. We want to see if we can turn that technology around and use it to prevent nutria from reproducing," McLachlan said. A big part of the CBR's efforts is raising public awareness of the issue of invasive species.
"We want to use the map as a starting point for a larger discussion about invasive species in Louisiana," said Liz Davey, Tulane's environmental coordinator. She's working with professors on campus to get the topic into the classroom, and is also coordinating the CBR's efforts to educate Louisiana politicians and the general public about invasive species. The hope is that when people are more aware, there will be more checks on the spread of invasive species.
On a small scale this could mean that gardeners will use native rather than exotic species and recreational boaters will empty bait buckets and clean plants off their boats and motors before moving to a new location. On a larger scale, importers and exporters could inspect and, if necessary, destroy containers and packing materials that could harbor invasive species, and ships and ports could initiate ballast water management procedures. And perhaps Louisiana diners will develop a taste for nutria.
Heather Heilman is an editor in university publications and a regular contributor to Tulanian.
Tulane University, New Orleans, LA 70118 504-865-5000 firstname.lastname@example.org