Report Shows Candlewood Lake is Free of Zebra Mussel Veligers

Candlewood Lake enthusiasts received some good news last week: the Lake is “substantially” free of zebra mussel veligers, the microscopic offspring of adult zebra mussels, according to a report compiled by scientists who collected and analyzed samples of the Lake’s water during the summer.

Zebra mussels are a hugely prolific aquatic invasive species that have infected the Great Lakes and many other fresh water bodies in North America. They were also discovered in the nearby Housatonic River impoundments of Lake Lillinonah and Lake Zoar in the fall of 2010.

Absence of the veligers is believed to indicate an absence of colonies of adult, reproducing zebra mussels, as well as the absence of imported water and equipment from other locations that might be contaminated and harbor the veligers.

“We found no substantial evidence that zebra mussel veligers are in Candlewood Lake,” explained Mitch Wagener, Ph.D., professor and Chairman of the Biology and Environmental Sciences Department at Western Connecticut State University (WCSU).

Dr. Wagener, along with Edwin Wong, Ph.D., of WCSU, and Larry Marsicano, Executive Director of the Candlewood Lake Authority (CLA), led the team searching for the veligers. WCSU students Melissa Garafolo, Catrina Morgan, Ana Bortoletto and Maria Bortoletto aided the project.

A single ‘suspect’

However, the team’s 30-page report also pointed out that the scientists identified what they initially believed to be a single veliger in a few of the early samples taken from Candlewood Lake. No veligers were found in the samples taken later in the summer. The researchers believe the ‘objects’ initially identified as veligers may have been ‘false positives’ since they were not found in the subsequent examinations of the same samples.

Zebra mussel veligers can be difficult to identify accurately, according to Dr. Wagener, due to: their extremely small size; their surface appearance, which is similar to other organisms and matter in the water column; the huge amount of background planktonic biomass in the water column; and the nuances of the methods that are available to identify the microscopic organisms.

The WCSU team utilized two identification techniques: cross polarization microscopy and polymerase chain reaction assay, better known as PCR, which utilizes pieces of the organism’s genetic material, or genes, as a means of determining if they were in a sample. The team also employed multiple viewing angles, multiple observations, and more than one observer. The result was the provisional identification of a single zebra mussel veliger in each of five of 18 samples taken from Candlewood Lake.

The team also tested water from Lake Zoar and found numerous veligers in some samples. Water samples taken from Lake Lillinonah revealed no suspected zebra mussel veligers.

Each water sample collected by the researchers contained plankton from roughly 1,100 liters of water. A single adult zebra mussel is believed capable of producing thousands of veligers a day –— so the discovery of a just a single veliger is considered unlikely.

Future testing

Marsicano said he was “extremely pleased” with the positive outcome of the pilot project, adding that “Dr. Wagener and Dr. Wong have now developed a very important expertise that will most likely be a regional asset for years to come.” Marsicano added that the lake water-monitoring project was a recommendation of the regional Zebra Mussel Task Force.

“Hopefully, this is just the beginning on a long-time and comprehensive monitoring program for zebra mussel veligers, both in Candlewood Lake and in other nearby waters.” added Dr. Wagener.

“We hope to continue this study in the year to come and collect samples earlier in the season, so that we might better understand the timing of the zebra mussel reproduction cycle, and in more locations, so that we can better pinpoint the possible spread of the veligers as well as the possible locations, if any, of colonies of adult reproducing zebra mussels.” 

He said the additional high priority collection sites are near boat ramps and docks, where boats that may be infected enter the Lake, as well as elsewhere in the Housatonic River.

“Additionally, now that the best primer sets have been identified for PCR, we expect that DNA analysis will be increasingly fruitful in the next year in our identification efforts,” he continued. “As resources allow we will sequence the genomic DNA from the Candlewood Lake plankton community to add to the precision of the analysis."

The WCSU research team collected 18 samples of Candlewood Lake water on six separate occasions during the summer near the boat barrier separating the aquaduct where the intake structure is located and near Lynn Demming Park in New Milford. Zebra mussels are thought to reproduce only when water temperatures are above approximately 50 degrees fahrenheit.

Funding for this monitoring project was provided by the U.S Fish and Wildlife Service Aquatic Nuisance Species Task Force and administered by the CT Department of Energy and Environmental Protection Inland Fisheries Division Aquatic Nuisance Species Program. The CLA and the WCSU Biology and Environmental Sciences Department provided additional support.