Maryland's least wanted

A few voracious, invasive plant and animal species threaten to crowd out state's native life forms


Porcelain-white swans with gracefully sloping necks paddle among swaying reeds on Kent Island. But Jonathan McKnight doesn't see fairy-tale beauty; he sees an invasive species more menacing than snakeheads.

McKnight, Maryland's top expert on exotic species, said the threat posed by the Asian "frankenfish" has been exaggerated. The snakeheads don't walk (contrary to some reports), are not equipped to invade the salty Chesapeake Bay and are less toothy than the common bluefish.

But because the snakehead has an image problem, it is a useful illustration of a more subtle but very real threat to biological diversity posed by a growing number of non-native species, such as mute swans. These lesser-known invaders are quietly crowding out local life forms in Maryland, McKnight said.

"We have no actual evidence of any damage caused by the snakeheads, but we have 50 years of peer-reviewed science proving the extensive damage caused by mute swans," McKnight said. "Sooner or later, we'll end up with a planet with very few species, and these few species will be everywhere," he said.

McKnight, associate director for habitat conservation at the Maryland Department of Natural Resources, gave a tour of a "rogue's gallery" of Maryland's most aggressive exotic species, including Japanese knotweed and Iranian giant hogweed. As he drove around the state, he showed evidence of troubling trend.

Just as generic-looking chain stores are crowding out family-owned businesses, a small number of animal and plant species that can eat virtually anything and live almost anywhere are threatening to snuff out the Chesapeake region's most unusual life forms. Many of the local species are vulnerable because they have limited diets and can live only in a specific area.

Mute swans, imported from Europe four decades ago to decorate lawns, drove away Maryland's last colony of black skimmers, a threatened bird species.

Japanese knotweed is devouring hillsides and crowding out native indigo bush. Purple loosestrife from Asia is monopolizing wetlands around the bay, overwhelming three-square rushes, among other local plants. Ratlike nutria from South America devour wetlands, wrecking the breeding grounds of black ducks and fish.

"It's becoming the United States of Generica," said McKnight. "Mom-and-pop diners are disappearing and being replaced by McDonald's and other chain restaurants everywhere you look. In nature, we have the same thing going on. We are creating a new era of extinction by homogenization."

Plants and animals have always moved from place to place and competed with one another, McKnight said. But that natural Darwinian process has been thrown out of balance by ships and airplanes, which have helped a few successful species spread like viruses.

The first stop on McKnight's tour was near a marina on Kent Island. He hopped out of his state-issued sport utility vehicle and pointed to a fuzzy gray cygnet paddling behind five adult white swans.

McKnight explained that five mute swans were brought from Europe to Maryland in 1962 to serve as lawn ornaments for an estate in Talbot County. They escaped during a storm and over the next four decades reproduced so quickly that the state now has about 3,500.

"The swans are extremely aggressive. They'll go after other birds, and they feed entirely on submerged aquatic vegetation, which is an important but declining resource in the Chesapeake Bay," McKnight said.

Despite a lawsuit by animal-rights activists, state biologists have destroyed about 8,400 mute swan eggs over the past four years. The scientists have spotted about 1,400 nests from airplanes, then slogged in on foot to spray the eggs with vegetable oil, which suffocates the embryos.

McKnight drove over the Bay Bridge into Annapolis, stopping at his office at the Department of Natural Resources. There, in the lobby, a snakehead swam in a tank.

The slender fish, about a foot long with patterns of green diamonds along its side, is considered a delicacy in China. The fish caused alarm when several popped up in a Crofton pond in 2002 and the Potomac River this year, perhaps dumped there by people with aquariums, McKnight said.

Don Cosden, a state fisheries biologist, gazed into the tank and said the snakehead poses little threat to the Chesapeake Bay. "It's a freshwater fish and so it presumably can't tolerate the salinity at the mouth of the Potomac. So it couldn't travel into the Chesapeake Bay," he said.

One risk posed by snakeheads is that they will compete with largemouth bass, which is also an invasive species, introduced into the Potomac by sportsmen a century ago. Globally, the bass have a worse record for ecological destruction than the snakeheads, using their huge, cagelike mouths to snap up baby birds, McKnight said.

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