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Lake Host program aims to stop spread of invasive Asian clams in N.H.

Asian clams.
(Courtesy of Amy Smagula, New Hampshire Department of Environmental Services)

Asian clams. (Courtesy of Amy Smagula, New Hampshire Department of Environmental Services)

The invader may be small – merely the size of a quarter – but the Asian clam can have a devastating impact on New Hampshire’s bodies of water, officials say.

The invasive species has been colonizing lakes, ponds and rivers across the state for the past several years. And this summer, three paid or volunteer specialists known as Lake Hosts in Loudon – who stand guard at the Clough Pond state boat ramp – are paying special attention to the species, educating boaters on ways to prevent the clam from taking up residence in town.

“When you come to the pond this summer, be safe, vigilant, and thankful that we have a clean pond,” says an article in the Loudon Ledger that introduces the Lake Hosts and warns of the clams.

The Asian clam first popped up in New Hampshire about five years ago at Cobbett’s Pond in Windham, and the invasive species soon spread to bodies of water across the state, including Long Pond in Pelham. In 2011, they showed up in the Merrimack River along a stretch through Bow and Hooksett, and now have about 99 percent cover along that part of the riverbed, said Amy Smagula with the state’s Department of Environmental Services. “They are starting to crop up in more locations,” she said.

Once the clams get into a body of water, they rapidly reproduce and colonize along the bottom, which can damage the health of aquatic ecosystems, pose public safety problems and lead to potential economic impacts.

The clams “tend to become dominant and compete with other native species for resources,” Smagula said. Each individual clam – yellowish in color – can filter feed a quart of water each day, stripping out all of the microscopic organisms and plankton that make up the base food supply of the aquatic ecosystem. “It impacts fisheries, insects, it changes the entire water column,” she said.

The clams prefer to colonize in sandy sediment close to the shoreline, which is typically along beaches where swimmers run the risk of cutting themselves on the clams’ sharp shells, Smagula said. Another worrisome health effect is the clams’ potential to cause algae blooms, full of harmful bacteria.

“The impacts are varied: aesthetic, recreational, human health, and the economics of it could be far reaching,” Smagula said. “People may not want to go to a lake that has invasive animals.”

Since the clams first appeared in Cobbett’s Pond several years ago, residents have noticed a multiplying population. Between last year and this year, the number of locations where people have seen the clams doubled, from five to more than 10 in the 46-acre pond, said Mike Brown, who is on the pond improvement association’s water quality committee. But the town has yet to see any major impacts.

“We haven’t yet seen the full effect. . . . It’s more of a concern of what could happen,” Brown said.

But residents have noticed fewer of the big, black mussels that are native to the pond, he said. Kids who swim in the water usually wear shoes to protect their feet from cuts from the open, sharp shells.

“Right now it’s a nuisance,” Brown said.

The clams rank among the top five invasive aquatic animal species that the DES is trying to manage by stopping their spread and preventing further growth of the existing colonies, Smagula said. Others include the Chinese mystery snail – already present in several lakes and ponds in the southeastern part of the state – and the spiny water flea, zebra mussels and rusty crayfish, which haven’t yet crossed the border into New Hampshire.

But, as in many cases, preventing their spread is easier said than done. The round, ridged Asian clams may grow to be quarter-sized, but they have a microscopic life phase. That means during reproduction, the clam larvae are tiny, not visible to the naked eye, and can be easily transported in something as small as a drop of water.

“Anyone that has gear – anchors, bait buckets with any lake water in it – could be picking up larvae and transporting them from an infested water body to a clean one,” Smagula said.

DES along with the New Hampshire Lakes Association have launched various education efforts, like the Lake Host program Loudon employs, to inform boaters about the precautions they can take to stop the spread.

For the invasive animals in particular, officials recommend that boaters wash and then dry their boats, leaving them out of water for up to five days to make sure the invasive hitchhikers perish before making it to a new water body.

“Science has shown that drying at least five days kills most of the stuff we’re concerned about,” said Andrea LaMoreaux, vice president of the New Hampshire Lakes Association in charge of the Lake Host program. That effort has long focused on stopping the spread of invasive plants, such as milfoil, but really began educating boaters about invasive animals and Asian clams last year. “We really kicked it up a notch,” LaMoreaux said.

The Asian clams were first discovered in New Hampshire several years ago, but they have been making their way through the country for the past 60 to 70 years. Officials suspect the species was brought to the U.S. through the Asian food market, Smagula said. “For a long time we thought that we in New Hampshire were at the northern part of their range, but they have been found farther north,” she said. “It’s not unexpected they will get a good foothold here.”

This year, DES hasn’t found any new Asian clam colonies in the state, but they aren’t letting up on prevention measures. “It could be the next boat ride away,” Smagula said.

(Allie Morris can be reached at 369-3307 or at amorris@cmonitor.com.)

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