10 most wanted
Beware of the invaders of the Chesapeake
By PAMELA WOOD, Staff Writer
NEWBURG -Jonathan McKnight bent over a series of holes dug into the shoreline here along the Wicomico River, looking for evidence of orange-toothed rodents called nutria.
The furry critters are native to South America, but they’ve devastated wetlands on Maryland’s Eastern Shore with their voracious appetite for marsh grasses.
The last thing Mr. McKnight wanted to see is signs that nutria have crossed the Chesapeake Bay.
There were no tracks, there was no scat and the holes weren’t quite the same as the ones nutria make.
His conclusion: probably muskrats — a native marsh rodent that doesn’t ruin the environment.
“I think you had muskrats in profusion, but they appear to have moved on,” Mr. McKnight told the relieved homeowners.
It’s a long trip from the Maryland Department of Natural Resources headquarters in Annapolis to this hamlet in southern Charles County, but for Mr. McKnight it was worth it to know that nutria aren’t here.
He gets scores of phone calls of nutria sightings each year, and visits about half a dozen of the most credible tips. Usually, it turns out not to be nutria at all. And that’s the way he wants things to stay.
“You go. You look. It’s muskrat,” he said. “But the price of not going is you miss them when they’re just getting established.”
For more than 50 years, wildlife officials have struggled to eradicate nutria from the Eastern Shore. They were brought here in hopes of helping the fur industry. Eventually the critters got out, and it’s been bad news for marsh grasses ever since.
Nutria are just one of scores of nonnative species that have invaded the Chesapeake Bay watershed.
Some are ugly, like the nutria and the furry mitten crabs.
Still others are beautiful, like the elegant mute swans or the graceful curves of the rapa whelk’s shell.
No matter what they look like, they aren’t from here and don’t belong here, according to wildlife officials. Some are doing a doozy on the bay’s natural ecology, and it’s darn difficult to get rid of them.
All told, there are about 160 nonnative plants and animals that have become established in the Chesapeake Bay region, according to Dr. Gregory M. Ruiz of the Smithsonian Environmental Research Center.
Some are known to cause major damage to the environment, such as the grass-gobbling nutria and the mute swans that obliterate underwater grass beds.
But most nonnative species have more question marks next to their names than answers, Dr. Ruiz said.
“We don’t know what most of them do ecologically,” he said.
Figuring out what nonnative species do, how they get here and how to prevent more from arriving is the focus of research by a growing number of scientists.
Tom Smith, director of natural heritage at Virginia’s Department of Conservation and Recreation, has seen increased attention to his field.
“People have been getting more aware of the economic impacts of these species, and not just the environmental impact,” he said. “There’s more species that are having a direct impact on landowners.”
Mr. Smith knew the concern was going mainstream when he saw invasive species on the cover of Parade magazine.
“When I saw that, I thought, ‘OK, it’s starting to hit mainstream America,’” Mr. Smith said.
Harmful nonnative species have been showing up in the news more frequently.
The infamous northern snakehead fish earned headlines from coast to coast when it was discovered in a Crofton pond in 2002.
The toothy invader was dumped in the pond by a man who had bought the fish for its supposed medicinal purposes.
Snakeheads are native to Asia. The toothy snakeheads have the uncanny ability to survive out of water for a short time if they burrow themselves into a muddy or damp area. They also can slither a short distance out of water.
Mute swans are another headline species, in part due to the controversy around how to get rid of them.
Maryland’s efforts to eradicate mute swans took a path through federal courts and even the U.S. Congress, which changed the law to allow wildlife managers to ruin eggs and shoot adult birds.
Some animal rights advocates protested the killing of mute swans, but wildlife officials argued the birds ruin underwater grass beds and crowd out birds that are supposed to be here.
A new addition to the list of nonnative stars is the emerald ash borer, a tiny green beetle that ruins trees.
It appeared in Prince George’s County a few years
ago, and wildlife and forestry officials are working feverishly to
keep the beetle from spreading.
When the trees die, there’s less filtering and slowing of water that rushes toward the streams.
There are plenty of lesser-known invaders, too.
Take the rapa whelk, a large predatory snail that has a conch-like shell.
Though they’re not in Maryland, rapa whelks are well-established in the waters in the Hampton Roads area of the southern bay, where they feast on clams and oysters.
The Virginia Institute of Marine Science even offers a bounty for watermen who turn in rapa whelks: $5 alive and $2 dead.
Since 1998, some 14,000 rapa whelks have been collected in that area, said Dr. Roger Mann of VIMS.
“When you’re catching those numbers, it’s only a matter of time before they expand out from Hampton Roads,” he said.
Rapa whelks likely came here in the ballast water of ships bringing coal into the bay, Dr. Mann said.
Points of arrival
Industrial shipping is a common route for many invaders.
It’s one of the theories behind the recent discovery of Chinese mitten crabs in the bay.
Large ships have tanks of water that are used to balance the ship’s weight. Ballast water is collected and released at various points in a ship’s journey — opening the door for tiny critters to move around the world with the water.
Other shipping-related means of arrival include critters
getting stuck on a ship’s hull or coming in with dry ballast
such as rocks and sand.
The Maryland Association of Pet Industries encourages pet stores and dealers to take back unwanted pets to prevent dumpings in the wild.
Another problem is aquaculture experiments gone awry. For example, the oyster-killing pathogen MSX might have arrived in the Chesapeake decades ago with Pacific oysters that were introduced.
And finally there are the animals that escaped from captivity — such as the five Eastern Shore mute swans that fled during a storm in 1962.
While there are scores of nonnative species making their homes here and causing trouble, the Chesapeake isn’t the worst off in the country for invaders.
San Francisco Bay is something of a hotspot, Dr. Ruiz said, because of extensive experiments with different oyster species.
Dr. Ruiz’s team at the Smithsonian’s Edgewater campus is constantly updating an online database of nonnative species.
It started with the Chesapeake Bay and has grown to include invaders in 26 other American bays.
“The number of species continues to grow,” Dr. Ruiz said. “From a basic science point of view, they’re a player and they’re becoming a bigger player.”
Called the National Exotic Marine and Estuarine Species Information System, the database has a fitting nickname: NEMESIS.
Mitten crab (Eriocheir sinensis)
Where it belongs: China.How it got here: Three have been found in the Chesapeake Bay in recent years, possibly landing there through ballast discharge or human discards.Offense: Burrows into riverbanks, causing erosion. Steals bait, messes with watermen’s nets and traps for other species. Unclear how it would affect native blue crabs.
Nutria (Myocastor coypus)
Where it belongs: South America.How it got here: Brought to Maryland’s Eastern Shore for experiments on farming them for their fur. Some of the orange-toothed rodents were released or escaped.Offense: Obliterates marsh plants, ruing vital wetlands. Blackwater National Wildlife Refuge near Cambridge has lost 7,000 acres of salt marsh since 1940.
Asian clam (Corbicula fluminea)
Where it belongs: Indonesia, Philippines, probably also Africa and Australia.How it got here: Released in ballast water from ships or brought here for food.Offense: Clogs pipes at power plants and water treatment plants in freshwater areas.
MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus)
Where it belongs: Still being studied.How it got here: Unclear, but possibly through transport of oysters, shell or seed.Offense: These two parasites attack oysters and are among the culprits of the precipitous decline of the native oyster population in the Chesapeake.
Northern snakehead (Channa argus)
Where it belongs: East Asia.How it got here: Discovered in a Crofton pond in 2002, dumped by a man who bought it from a fishmarket for medicinal properties. Since found in other waterways, including the Potomac River.Offense: Toothy predator has the ability to live in mud and wriggle short distances.
Mute swan (Cygnus olar)
Where it belongs: Europe, Asia.How it got here: Five pet birds escaped from a Talbot County farm during a storm in 1962 and have reproduced like mad ever since.Offense: Gobbles underwater grasses, crowds out native birds. Known to attack humans who come near.
Emerald ash borer (Agrilus planipennis)
Where it belongs: Eastern Russia, northern China, Japan, Korea.How it got here: Probably came to America through shipping — either in ash wood used to stabilize ships or in packing material. Arrived in Prince George’s County in 2003 after infested trees were illegally shipped here from Michigan.Offense: This beetle is responsible for the loss of 25 million trees in the Midwest and 25,000 ash trees have been removed in Prince George’s County. Ash trees make up 20 percent of streamside trees in Maryland, which are vital to the health of the Chesapeake Bay.
Zebra mussel (Dreissena polymorpha)
Where it belongs: Russia, Ukraine.How it got here: Released from ballast water from ships, first in the Great Lakes. Not widespread in the Chesapeake, but officials are concerned the population may grow in freshwater and low-salinity areas.Offense: Colonizes in intake pipes at power plants and water treatment plants; attaches to boats, docks and buoys, eats microscopic zooplankton that forage fish depend on.
Asian oyster (Crassostrea ariakensis)
Where it belongs: Japan, China, India, Pakistan.How it got here: Scientists are studying whether to introduce the ariakensis oyster to boost the flagging population of the native oyster. The bay’s test oysters came from the West Coast, where they’ve also been studied.Offense: Questions remain regarding how this oyster would interact with existing species and whether it would have negative effects on the ecosystem.
Rapa whelk (Rapana venosa)
Where it belongs: Northeast Pacific Ocean.How it got here: Released in ballast water from ships or hitchhiked with an imported oyster. Well-established population in the southern bay in Virginia’s Hampton Roads area.Offense: Eats hard clams and, to a lesser extent, Eastern oysters.
(Revised May 2007)