The greatest enemy to Eastern Shore wetlands today may not be a bulldozer blade, but the sharp teeth of a small rodent.

The muskratlike nutria was brought to the region in the 1930s in a failed attempt to prop up the fur industry. Today, it is on the loose, chewing up marsh grasses, allowing hundreds of acres of wetlands to erode away a year.

The nutria’s voracious appetite — along with its ability to rapidly reproduce — has earned it a place on a new Bay Program list of “least wanted” plants and animals.

Its Invasive Species Workgroup recently identified nutria and the five other problem species that constitute the greatest ecological and environmental threats to the Bay and its watershed.

By the end of this year, the workgroup will develop management plans to control the spread of those species. The list, and the management plans, were called for under a Chesapeake 2000 agreement commitment to control species “deemed problematic to the restoration and integrity of the Bay’s ecosystem.”

Besides the nutria, the list includes two wetland-damaging plants, phragmites and purple loosestrife, two species that threaten underwater grass beds, the mute swan and the water chestnut, and the ecosystem-altering zebra mussel.

Like the nutria, each species has the potential to rapidly multiply and dominate areas where they are found, threatening native species and resources, such as wetlands.

Beyond the six least wanted species, the workgroup identified another 29 species that constitute a “watch list” and could get more coordinated attention in the future.

Concerns about so-called “biological pollution” have been growing for years as alien species have crowded their way across the nation’s landscape and through its waterways, often with more devastating impacts than chemical pollution.

Nonetheless, responsibility for trying to deal with invaders is scattered among more than a score of state and federal agencies, and control efforts have historically been poorly funded — at least in part because the issue of dealing with entrenched invaders seems intractable.

“One of the stumbling blocks to making exotic species a greater priority in agencies is the overwhelming task and the expense,” said Edith Thompson, a biologist with the Maryland Department of Natural Resources who chaired the workgroup. “We wanted to identify some chunks of the problem that are already on the radar screens of surrounding jurisdictions to help ensure that coordinated control of the top six species could occur, because no one agency or jurisdiction can manage this issue alone.”

The Bay Program effort represents the first time that jurisdictions in the region have agreed to work together to control specific nuisance species.

If the region can successfully coordinate monitoring, control, and mitigation of damage with a few of the most problematic species, Thompson said, it will bolster confidence that the problem can be dealt with.

Exactly how those species will be controlled remains to be seen. The Bay Program is planning a workshop in late spring to start the job of drafting specific management strategies.

After that happens, the test will be whether state and federal agencies can turn paper plans into action, said Mike Fritz, living resources coordinator with the EPA’s Bay Program Office. “The challenge in the management plans is whether there will be a commitment to implement them by the partners.”

Concern about exotic pests isn’t new. More than 250 years ago, leading Colonial botanist John Bartram established the first botanical garden in the New World just outside Philadelphia, planting it with species gathered from his own journeys throughout the colonies, and with plants send by friends in England.

But the botanist noticed a side effect of his garden. The foreign plants, he noted in a letter to a friend, “have escaped out of our gardens and taken possession of our fields and meadows, very much to our detriment.”

Bartram was a visionary. Today, exotic species have flooded the Bay and its watershed. In Pennsylvania, more than a third of the more than 3,000 plant species originated from somewhere else. About 150 species in the Chesapeake Bay are nonnative.

Nationwide, an estimated exotic 4,500 species of plants and animals have established free-living populations. Not all those species are harmful. Some seem fairly innocuous, such as Queen Anne’s Lace, which has quietly become a part of the natural landscape, fitting in without squeezing anything out. Others serve human interests: In the water, imported species such as channel catfish and brown trout are prized recreational species. On land, species such as wheat and cattle are the foundation of the nation’s agricultural economy.

The problems stem from a smaller number, less than 15 percent by some estimates, that become “invasive” — rapidly infesting, and altering, ecosystems. For the most part, invasive species are nonnatives which either come from another continent, or another region, where their populations were kept in check by parasites, predation or environmental conditions.

When they are moved, and freed from those natural controls, they can run wild. Like the wetland-chewing nutria or the underwater grass-chomping mute swan, they can so overwhelm an area that they actually destroy the habitats they depend upon.

Others, like phragmites and purple loosestrife, can form thick monocultures, crowding out native plants and the wildlife that depend on them, thereby reducing the area’s biodiversity.

Aggressive plant invaders can reduce the amount of light, water, nutrients and space available to native species. They can also alter soil chemistry, increase erosion, change hydrology and — in parts of the country — change the natural fire regimes which some native species depend upon.

Globally, scientists say the greatest threat to native biodiversity is habitat destruction. The second greatest threat is the introduction of exotic species: The U.S. Fish and Wildlife Service has estimated that 42 percent of the nation’s endangered and threatened species have declined because of competition from exotic plants or animals.

Some plant and animal invaders harbor pathogens which affect native and nonnative plants alike. The colorful flowers of some invasive flowers can lure pollinating insects away from natives. And in some cases, the exotics contain toxins that may be lethal to certain animals. For example, the leaves of the invasive garlic mustard are lethal to the eggs of the West Virginia white butterfly, a rare species native to the watershed.

Some are economic threats. The European green crab, a predator of clams and other bivalves, has been associated with the demise of the soft-shell clam industry in New England. Industries and power plants spend tens of millions of dollars annually trying to keep clusters of zebra mussels from clogging their pipes.

David Pimentel, a scientist at Cornell University, has estimated that invasive species cost the economy about $122 billion a year through economic losses and associated control costs.

But then, no one needs to tell the Bay region about the potential impacts from exotics: Its most ecologically and economically important native species, both on the land, and in the water, met their demise largely because of foreign invaders.

The American chestnut, once the most common and most valuable species in the region’s forests, was wiped out by the chestnut blight fungus which was imported on shrubs from Asia in the early 1900s. Lost with it was half the timber value of Eastern U.S. forests. It was also the most important nut-producing tree for wildlife.

In the Bay, the native oyster was devastated in large part by the parasite MSX, which was inadvertently brought to the region in the 1950s, probably on foreign oysters. The Bay once produced more oysters than the rest of the world combined, and the bivalves were able to filter all of its water in a few days.

Today, the oyster fishery — once the Bay’s most valuable — is largely gone, and the Chesapeake suffers degraded water quality and the loss of important habitats.

Despite the problems, experts believe the invasive species situation could get worse.

“Increased travel and global trade have resulted in growing numbers of invasive species gaining entry into the United States,” said a recent report by the Congressional General Accounting Office. “Expanded trade within North America has also increased the risk of spreading established invaders from one country to another.”

The issue reached the presidential level in February 1999, when President Clinton issued an executive order establishing a National Invasive Species Council to coordinate federal actions.

Among its goals: Increase inspections of incoming goods and take other actions to prevent new invasions.
In 2000, the federal government spent about $149 million on rapid response efforts. But the potential costs of doing nothing are even higher, the GAO report noted. If the tree-destroying Asian long-horned beetle, which has turned up in packing crates from China, were to become firmly established, it alone could cause annual damages of $138 billion in the United States.

On the water, the federal government is considering the tightening of the rules for managing the release of ship ballast water, which is a prime method for moving aquatic species — and pathogens — around the globe. The Bay Program last year issued a report urging Congress to pass a law regulating the discharge of ballast water in the nation’s water.

While the federal government steps up efforts to hold the line on new invasions, the Bay Program strategy is to begin coordinated efforts focused on the biggest pests already here.

Historically, there has been little cross-border cooperation on issues of exotic species: While the sale of purple loosestrife is banned in Pennsylvania, it is legal in Maryland.

õith state budgets limited, and a potentially lengthy list of problem species to look at, the Invasive Species Workgroup picked its targets through a survey of all the Bay Agreement signatory jurisdictions (Pennsylvania, Virginia, Maryland and the District of Columbia), as well as New York, New Jersey, West Virginia and Delaware, and federal agencies.

It asked each to list the five invasive species present in their state causing the greatest ecological or economic impact, as well as five problematic species they considered likely to enter their state.

The final target list included most species that were listed as a top priority by two or more jurisdictions. Also, the selected species threaten “trust” resources which are the government’s responsibility to protect, such as wetlands and underwater grasses — dandelions may be invasive, but they don’t threaten much besides yards.

That doesn’t mean other species are not problems, workgroup members said. “We can’t address everything that we might like to address,” said Leo Dunn, a workgroup member from the Pennsylvania Department of Agriculture. “We had to prioritize it in order to have some hope of getting enough money and cooperation to actually have an impact.”

Dunn, who also serves on the federal Aquatic Nuisance Species Task Force, which is aimed at dealing with the spread of marine and freshwater pests, said places that have had success with exotics are those which had an agreement on specific species.

Last year, for instance, state and local communities in California banded together to eradicate a highly invasive foreign seaweed that turned up in coastal waters.

For most of the problematic species on the Bay list, though, eradication is not an option. Plants such as phragmites and purple loosestrife are too widespread. And in some cases, such as attractive mute swans, eradication may be too politically unpopular to be pursued.

The bad news, Dunn acknowledged, is that management will mean an ongoing expense for agencies already facing budget cuts. But by working to keep problem species in check, he said, managers leave open the possibility that research may find new, more effective means to control, or eliminate, the species.

“Part of any control plan is more research,” he said. “There is always a long-term hope that information will change enough that you can do more. But if you just forget about it, then you basically have said that at no point will we be able to eradicate it.”

Leaving problem species unchecked also creates problems, Dunn said. For example, if phragmites invaded the Maryland and Pennsylvania wetlands that hold most of the remaining populations of the threatened bog turtle, the sites would probably be so altered that the turtles would be eliminated — or require major intervention to protect.

Dunn said that for now, the region needs to show that it can actually do something about nutria, phragmites, purple loosestrife and the other “least wanted” species the workgroup has targeted.

“This is the starting point for cooperation on the species level,” he said. “Getting these six species and their management plans is like a demonstration project. We need to make this work before we got off and look at anything else.”

But if the states can demonstrate success, Thompson said they may be able to eventually create a formal standing panel to work regionally with the federal government to control invasive species — something that has happened in other parts of the country — and could lure increased federal support. “We are trying to generate momentum to get all the jurisdictions that need to be involved in some kind of forum talking about it,” she said.