Asian Clams Are Here to Stay: Living with Lake George's Latest Invasive

The Lake George Park Commission’s annual lake-wide invasive species survey, conducted with volunteers over a course of four days in August, found a colony of Asian clams entrenched across a 20-acre site at the mouth of Hague Brook. It is now one of 24 known sites in Lake George infested with Asian clams. 

The discovery was not entirely unexpected, said Walt Lender, the Lake George Association’s executive director.

According to Lender and other members of the Lake George Asian Clam Task Force, which was created in 2010, when the aquatic invasive species was first discovered here, Asian clams reproduce frequently and profusely.

If there was an established colony nearby, and there was, some could be expected to migrate to other sites and reproduce there, especially if the habitat is suitable,” said Lender.

Currents, winds and waves can transport Asian clams suspended in the water column to new locations some distances away, said Dr. Sandra Nierzwicki-Bauer, the associate director of RPI’s Darrin Fresh Water Institute and now one of Lake George’s foremost authorities on Asian clams.

Nierzwicki-Bauer also said the species prefers a sandy, gravelly lake bed, such as the one at the mouth of Hague Brook, where a delta has formed.

Based on its characteristics –a sandy rather than a rocky bed - the site would also appear to be one where benthic mats might be deployed, successfully, to kill the population.

Dave Wick, the Lake George Park Commission’s executive director, however, said the task force has no plans to attempt to eradicate the newly-discovered colonies with treatments.

Benthic Mats: Ultimately, Ineffective

Nierzwicki-Bauer recalls that in 2010, the best information available at the time indicated that the most effective way of eradicating Asian clams was to smother them under benthic mats.

It was understood that the treatment would be most likely to be effective if sites were, like deltas and beaches, relatively free of rocks and, if possible, other obstructions, such as docks.

Under the benthic mats, we had incredibly high kill rates,” said Nierzwicki-Bauer. “But if even a few individuals survived, they would reproduce and repopulate the site.”

Lake George Waterkeeper Chris Navitsky added, “you can kill 99% of the clams, but the one percent that survives will spew forth 5,000 veligers.”

Benthic mats were installed at several sites from Lake George Village to Rogers Rock, at a cost of hundreds of thousand of dollars.

Suction harvesting and even an instrument that exposed clams to boiling water were also tried, with even less success.

At one point, the weather intervened, allowing some observers to believe that Lake George might lie outside the natural range of the Asian clam. Researchers at McGill University in Montreal had found that Asian clams could not survive for more than 60 days in extremely cold water, and after one severe winter, it was thought Lake George might be a body of water that produced those conditions. A summer of temperatures within historic norms, however, reversed those gains. Populations rebounded.

No Good Strategies

Wick, the Lake George Park Commission’s executive director, said the size of the area in Hague where the clams have settled is among the reasons why no treatments are planned.

But given the costs of installing benthic barriers, no site, even relatively confined sites with concentrated populations, are regarded as suitable for treatments.

Given that Asian clam control and eradication efforts cost between $60 to 80,000 an acre, the cost of treating Asian clam-affected areas lake-wide is cost-prohibitive and logistically beyond our current management abilities,” he said.

According to Wick, it has been decided to refrain from any largescale treatments until more has been learned about the Asian Clams’ reproductive cycles and the means by which it spreads from one section of the lake to another.

Asked if she agreed with other members of the task force that treating Asian clams with benthic mats was no longer feasible, Nierzwicki-Bauer said, “I do. It costs too much, especially without some guarantees of success.”

Asked for alternatives, Nierzwicki-Bauer said, “I don’t know that, at this point, we have any good concrete strategies to put out there.”

What the Science Does, and Does Not, Tell Us

Seven years after Asian clams were discovered near a beach in Lake George Village, it appears they’re here to stay.

Nierzwicki-Bauer said the Darrin Fresh Water Institute “has shifted its attention to learning more about the basic biology of Asian clams in Lake George. You can read about the species in the scientific literature, but there will be variations among different water bodies.”

Scientists are working on identifying differences in the relative health or robustness of separate colonies, making it possible, perhaps, to determine which populations might be most susceptible to eradication treatments of some sort should they become available.

Nierzwicki-Bauer and her colleagues have also completed a scientific paper on Chaetogaster limnaei, a two-millimeter-long parasite that feeds on the gills of juvenile Asian clams.

By conducting laboratory experiments, the team knows that the worm can reach the clams through the water column and can be transmitted from one clam to another.

Whether the worm can be used as a natural or biological agent against the Asian clam, is however, another question.

I don’t know that we have enough information to really know its impacts,” said NierzwickiBauer. “We do know the worm eats juveniles, but whether it can eat enough juveniles to have a big impact on the population, we can’t say at this point,”

Also unknown: the impact upon native mussels if the lake were to be stocked with worms.

Managing a Chronic Condition

Although the Asian clam has established itself in Lake George, the population has not grown to the levels seen in other lakes, such as Tahoe.

The Lake George Park Commission’s Dave Wick, for example, noted in his report that other than the colony found at the mouth of Hague Brook, the survey could find no other new Asian clam sites.

The population isn’t exploding,” said Walt Lender of the Lake George Association. “The winter freeze knocks the population back somewhat, even though we know we can’t rely upon that to eradicate the clams altogether.”

We have to live with the Asian clam, manage it as best we can and limit its spread,” said Waterkeeper Chris Navitsky. “We know that anchors are possible vectors. If sediment is attached to boat anchors, and the sediment contains veligers, then they can move from one site to another when the boat anchors at a different location. We have to remind boaters that they have a role to play in curbing the growth of the Asian clam population.”

Walt Lender said his organization is monitoring any detrimental effects the Asian clam might have on Lake George’s water quality.

In other lakes, the Asian clam appears to intensify the decline in water quality by releasing nutrients and fostering the growth of algae, said Nierzwicki-Bauer.

The shells of dead clams can also become a source of calcium for Zebra mussels and other invasive mollusks, creating micro-climates where the non-natives can mature and reproduce, she said.

Among the things limiting the spread of Asian clams is the lake’s natural characteristics, said Nierzwicki-Bauer.

Since the species’ preferred habit is sandy, gravelly bottoms, it will find those conditions only in portions of the lake, primarily in developed areas where deltas have formed or artificial beaches have been constructed.

Asian clams now occupy approximately 120 acres of lake bed, the “2018 Asian Clam LakeWide Survey: Final Report,” states.

Prevention: Less Expensive Than Treatment

According to Walt Lender, the expense of attempting to eradicate Asian clams, and the failure to do so, is proof, if proof were needed, of the value of programs such as the Lake George Park Commission’s boat inspection and decontamination stations.

One dollar spent on prevention is equal to ten times that amount spent on management, said Lender.

If new invasive are not prevented from establishing themselves in Lake George, the costs of managing the various species will only escalate, said Lender.

Of course, some might argue, the costs of failing to manage invasive species – to the ecosystem, to water quality, to the resort economy – may be even greater.