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Invasion of the Aliens: Body Snatching Worms, Cold Winters May Rout Lakes’ Enemies

Body snatcher: The worm Chaetogaster limnaei, viewed through a microscope. The worm has just eaten a young Asian clam, an invasive species in Lake George, N.Y. (Photograph: Dave Winkler) Public enemy number one, it might be called: Eurasian watermilfoil. It’s not on the FBI’s Ten Most Wanted list, but maybe it should be, say scientists...

Body snatcher: The worm Chaetogaster limnaei, viewed through a microscope. The worm has just eaten a young Asian clam, an invasive species in Lake George, N.Y. (Photograph: Dave Winkler)

Public enemy number one, it might be called: Eurasian watermilfoil. It’s not on the FBI’s Ten Most Wanted list, but maybe it should be, say scientists who study lakes. The invasive weed’s crime? It crowds out native underwater plants, fouls boat propellers and smothers swimming areas in freshwater lakes across the northern U.S.

The invader’s name strikes fear in the hearts of boaters, marina owners, bathers and fishers in places like Lake George in New York’s Adirondack Mountains. The 32-mile-long, mountain-ringed lake is known across the country as the Queen of American Lakes for its clean, clear waters.

Eurasian watermilfoil floats on the surface of a freshwater lake in the northern U.S.
Eurasian watermilfoil is a submerged aquatic plant that can form thick mats in shallow areas of lakes and rivers. (Photograph: Michigan Sea Grant)

To date, Lake George’s waters have been classified by New York State as AA-Special: drinking water. As far back as the early 1920s when biologists first conducted research on the lake, “readings showed that the water was unusually transparent,” the scientists wrote in a 1922 report, Biological Survey of Lake George, N.Y.

How long will this deep lake, a gift of the glaciers that covered the Northeast 10,000 years ago, remain unspoiled?

“That may depend on whether we’re able to keep out invasive species like Eurasian watermilfoil and Asian clams,” says Walt Lender, director of the Lake George Association (LGA), a group that works to safeguard the lake. The Asian clam, native to the fresh waters of eastern and southern Asia, is Lake George’s public enemy number two. The clam threatens more than Lake George; like Eurasian watermilfoil, it has made its way into lakes far and wide.

Answers are on the horizon, researchers say. Some may be hidden in the depths of Lake George. Others require far-reaching changes: a return to the cold winters of the past.

Plant-with-a-spear: Eurasian watermilfoil

Image of diver harvesting Eurasian watermilfoil on Lake George.
Diver working for Aquatic Invasives Management, LLC, harvests Eurasian watermilfoil in Lake George. (Photograph: Aquatic Invasives Management, LLC)

Eurasian watermilfoil is native to freshwater ecosystems in Europe, Asia and North Africa. The plant, also called spiked watermilfoil for its “spear” that extends above the water’s surface, was discovered in Lake George in 1985.

This year, divers working for the Lake George Park Commission (LGPC) – a state agency that has joined forces with the LGA and The FUND for Lake George, an organization dedicated to protecting the lake – hand-harvested some 100,000 pounds of Eurasian watermilfoil. “That’s more than the weight of three school buses,” says Dave Wick, executive director of the LGPC. “So far, hand-harvesting has been the most successful way of keeping watermilfoil at bay.”

Marching in: Chinese mystery snails, spiny water fleas

Lake George location with high densities of Asian clams.
Lake invaders: Asian clams are retrieved from Lake George with a sieve. The clams may reach densities of 1,500 per square meter (1 meter = 3.3 feet) at some sites along the lake’s shore. (Photograph: Jeremy Farrell)

Eurasian watermilfoil and Asian clams haven’t invaded Lake George alone. Chinese mystery snails, spiny water fleas and curly-leaf pondweed have also arrived in force.

“As bad as that sounds,” says Eric Siy, executive director of The FUND for Lake George, “Lake George is surrounded by waterways with dozens of invasive species.” Lake Champlain has 50; the St. Lawrence River, 84; the Hudson River, 122; and the Great Lakes, 184, according to a report by The FUND.

“Take quagga mussels,” says Siy. “They’ve been called ‘zebra mussels on steroids.’ These mussels blanket the bottoms of the Great Lakes, and are largely untreatable. Now they’ve made their way into New York.”  But not Lake George – yet.

Last summer, according to Siy, Lake George had a quagga “near miss.” The mussels were discovered on a trailered boat coming into the Adirondacks from Lake Erie. The boat’s owners were about to launch at Lake Placid – less than 90 miles from Lake George – when the unwelcome stowaways were routed out.

Invaders on the shore

Invaders on the shore: Asian clams in Lake George.
Invasion of the Asian clams: Locations where the clams have taken up residence on Lake George, as of September 28, 2016. (Graphic: Courtesy, Lake George Association)

It’s the quagga’s mollusk relative, the Asian clam, that could become the bane of Lake George. One Asian clam can produce up to 70,000 eggs each year. Because the clams are such prolific breeders, they compete with native species for space on lake bottoms and for food in the form of plankton, ultimately affecting fish and other organisms higher up the food chain. If beds of Asian clams are large enough, the nutrients they recycle may fuel unwanted algae blooms.

On a warm summer afternoon, Dave Wick zoomed in on a park commission boat to pick me up at a dock near Lake George Village. We were off on a day of eradicating Asian clams and other invasive species. Wick and I headed for Warner Bay on the lake’s east side, where divers pulled up Eurasian watermilfoil and piled it into mesh bags.

Wick pointed to waters with little to no milfoil – clear with fish darting in and out of healthy native aquatic plants. Where milfoil choked the bay, the waters had turned dark. “Warner Bay is in better shape than it was, though,” offered Wick on a hopeful note. “We’ve found large patches of milfoil and removed them, returning the bay to more of a natural state.”

From Warner Bay, we crossed to the lake’s west side, stopping just north of Boon Bay at Cotton Point. There we lowered the boat’s ladder, climbed down a rung or two, then jumped into the water with sieves to sift sand for Asian clams. The clams, first found in the lake six years ago, thrive in shallow waters with sandy bottoms like those in Boon Bay.

Wick brought up a sieve filled with the invasive clams. The LGPC and other organizations tried to eradicate the clams by covering them with plastic mats weighed down with sandbags and steel rebar. “That worked, but only so well,” Wick admitted.

Naturally vanquished

Researcher collects Asian clams on a sandy beach on Lake George.
Darrin Fresh Water Institute researchers collect Asian clams weekly from May through December to monitor the clams’ growth and survival rates. (Photograph: Jeremy Farrell)

Could an aquatic worm with a taste for Asian clams do the trick? Researchers at the Rensselaer Polytechnic Institute’s Darrin Fresh Water Institute (DFWI) in Bolton Landing, N.Y., are studying the worm, named Chaetogaster limnaei. It’s the first species in Lake George known to prey on Asian clams. The work is funded by the LGA and the LGPC.

Chaetogaster slithers its way into the mantle cavity of an adult clam, explains biologist Sandra Nierzwicki-Bauer, associate director of the DFWI. There it eats developing young clams before they can be released into the water.

“The worms have been found in Asian clams in some places in the lake, but not in others,” she says. She compared Asian clams with and without worms at three Lake George locations to find out whether Chaetogaster could be used as a biological control.

The worms are a step ahead. They’re already doing the job.

In two of three study sites, adult clams weren’t infected by Chaetogaster. “We found abundant small, young clams at these two sites, so adults there were successfully reproducing,” says Nierzwicki-Bauer.

At the third site, Chaetogaster had settled into the adults’ gills. “This spot had very few juvenile clams,” Nierzwicki-Bauer says. Chaetogaster had presumably devoured the young while they were still inside the adults.

Bad news for the clams, Nierzwicki-Bauer says, is good news for the lake.

Chaetogaster eating juvenile Asian clam.
Chaetogaster to the rescue? Scientists may have discovered a way to halt the spread of Asian clams in Lake George. (Photograph: Dave Winkler)

“Now we need to figure out whether Chaetogaster was already here when Asian clams arrived, or whether it came in with the clams,” says Nierzwicki-Bauer.

The answer, she believes, will determine whether scientists and lake managers should consider moving Asian clams infiltrated by Chaetogaster to areas with clams that aren’t yet carrying the worms. “It may not be the be-all and end-all,” she says, “but it might do a lot to reduce the clams’ numbers.”

The ultimate fix, says Nierzwicki-Bauer, is addressing climate change. “Lake George is at the northern edge of Asian clams’ current range in New York,” she says. “Warmer winters – and warming lake waters – may be increasing the clams’ numbers by allowing more of them to survive into spring.”

A model for the country

Eurasian watermilfoil on a boat propeller; the weed could invade a new lake.
Boats being moved from one waterbody to another are among the ways invasive species take over new lakes. (Photograph: Michigan Sea Grant)

For now, the best hope for Lake George, or for any waterbody, says Wick, is to catch invaders before they sneak in. Toward that end, the LGPC, with the help of the LGA and The FUND for Lake George, is spearheading a mandatory Lake George invasive species boat inspection program.

Boat owners trailering their vessels to the lake must stop at one of several inspection points. The boats are carefully checked from stem to stern for evidence of invaders. “We’ve saved the lake from countless new invasive species,” says Wick, “and cut down on levels of current ones.” The program has become a model for others around the country.

Will boat inspections, along with Chaetogaster and other hoped-for new discoveries, be enough to keep the Queen of American Lakes’ waters clear for the next 100…1,000…10,000 years?

Late autumn view of the Queen of American Lakes, Lake George, N.Y.
Late autumn on Lake George. How long will the Queen of American Lakes’ waters be classified “AA-Special”? (Photograph: Jeremy Farrell)

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Meet the Author

Author Photo Cheryl Lyn Dybas
Award-winning science journalist and ecologist Cheryl Lyn Dybas, a Fellow of the International League of Conservation Writers, brings a passion for wildlife and conservation to National Geographic, Natural History, National Wildlife, BioScience, Yankee and many other publications, and is a Field Editor at Ocean Geographic. Eye-to-eye with the wild is her favorite place to be.