By Robert Layman
Tucked away behind the Book Brothers Farm’s corn fields near the Cogman Bridge in West Haven, the Poultney River meanders west before turning south into Lake Champlain. And nestled in the muck in certain areas throughout the river are mollusk populations that can educate biologists about the quality of area’s water and the health of its fish populations.
Paul Marangelo, senior ecologist for the Nature Conservancy’s Vermont chapter, says this landscape is important to study freshwater mussels because it contains the most biologically diverse area in Vermont for the mollusks. However, that diversity has declined.
At one sampling in 1998, Marangelo found eight of Vermont’s 18 species at the site. Sampling typically happens in the river between where it enters the lake and the first waterfall upstream.
Since 1998, he’s sampled four times — in 2007, 2008, 2011 — and was at it again last week to continue his research on a 150-by-22-meter plot that was divvied up into square-meter quadrats.
In 2007, he saw a decrease in live findings to six species, then five in 2008, and four in 2011. However, this year saw that decline stop with a finding of four species, with the evidence that two others have been in the area.
“It’s a pleasant surprise,” he said. “Since 1998, every time we’ve gone back, the numbers have been declining. It’s nice to see that the numbers haven’t changed since 2011.”
Overall, the mussel search yielded 63 individual animals, which is representative of about 2 percent of the total plot surveyed.
Marangelo said the small percentage is due to the methodology, which is designed to maximize precision and minimize effort, which helps protect the species during sampling.
One of the four species was the Lampsilis ovata, or pocketbook, which is listed as endangered in Vermont.
According to the U.S. Fish & Wildlife Service, over 70 percent of mussel species are extinct or imperiled, while 16.7 percent of mammalian species and 14.6 percent of bird species claim that status.
Though not as visible, mussels play an important role as water-quality indicators.
According to the Environmental Protection Agency, one adult mussel can filter up to 15 gallons of water a day, eating algae, plankton and silt.
“River health has to do with a complex set of factors,” Marangelo said.
A lab test of water provides limited information about the ecosystem as a whole, whereas mussel data provides a broader outlook due to their specific habitat and breeding requirements. Mussels are affected by a large array of variables.
They’re prey for various mammalian species like muskrats, and can be susceptible to water pollutants.
Female mussels are picky about what fish they send their larvae to. The larvae become parasites on their hosts’ gills before dropping off.
Biologist Michael Lew-Smith, who volunteered during this year’s study, said the Lampsilis species will mimic a fish lure to entice it, before spraying it with a parasitic larvae cloud known as glochidia.
If a mussel species population is down, that could mean a fish species is down too.
Murray McHugh, critical lands manager for the Nature Conservancy’s Southern Vermont office, who helped document this year’s survey, said most of the riverside from Carvers Falls into Fair Haven is conserved to maintain habitat stability.
More information can be found at the state’s mussel atlas: bit.ly/0817Mussels