Vermont's Freshwater Mussels

Uniqueness and Diversity, Now Under Siege
Heelsplitter, squawfoot, pocketbook, giant floater -- what do these colorful terms have in common? They are names for some of Vermont's 17 native species of freshwater mussels.

Like clams, oysters, snails and octopuses, mussels are in a group of invertebrate animals called mollusks. With body parts enclosed within two hard shells, an adult mussel spends its life anchored in river or lake bottom sediments, moving only with the aid of a muscular foot or by powerful flood currents that can dislodge and propel it downstream. While settled quietly in the stream bottom, a mussel captures oxygen and microscopic food particles in flowing waters, by filtering water through an opening (inhalent aperture) between the shells, then through internal gills and the digestive tract.

Reproduction in mussels is unique. Females release immature mussels (called glochidia) into the water, where these tiny creatures must attach themselves to fins or gills of particular fish species. Following a few weeks of attachment, the young mussels drop to the stream bottom and begin life as typical mussels. The eastern pearlshell can live 100 years or more, but most species live far shorter lives.

Freshwater mussels had, and still have, economic value as food, in the production of buttons and in the cultured pearl industry. While no Vermont mussel is directly used by humans today (except occasionally as fishing bait), their ecological value is great. Mussels serve as biological indicators of the health of our waters. Pesticides, heavy metals, agricultural nutrients, heavy loads of fine silts, and other pollutants will kill mussels or accumulate in their tissues, providing a warning to us of an unhealthy aquatic system.

A Plague on the Natives
As if chemical and organic pollution, dams, and collapsing stream banks were not enough, native mussels now have to contend with something akin to the bubonic plague -- zebra mussels. In just two years, zebra mussels spread throughout Lake Champlain, where they now attach themselves in great numbers to native mussels. This can result in death for the natives. In some parts of Lake Erie, zebra mussels have eliminated 90 percent of the native mussels.

Mussels have been evolving for millions of years. North America hosts nearly one-third (300 species) of all mussel species known. But there's trouble in our waters. Seventy percent of North American mussels are either extinct, endangered, or declining.

Vermont's mussels are a diverse lot. The dwarf wedge mussel is generally less than an inch and a half long, compared to the pink heelsplitter, which can grow to six inches. Some, like the heelsplitter, sport a long "wing" on the shell. The heelsplitter is also nearly flat, and rounded like a dinner plate. Some of our mussels are brightly colored. The black sandshell is long and narrow like a spear point. The pocketbook is heavy and almost round like a cobblestone. The fluted-shell has wavy ripples on its shell. When the eastern pearlshell is old, it is shaped like a human foot.

Ways to Discover More
Ways to explore for mussels include searching middens (dinner scrap piles) left by muskrats, peering through glass-bottomed buckets while wading in a stream, and floating along with mask and snorkel, or with scuba gear. Any means can be a pleasurable experience, especially on a hot summer day.

Vermont owes its relatively high diversity of mussels, unusual for New England, to the Lake Champlain Basin. Following the retreat of the last glacier, avenues of dispersal from the Great Lakes Basin allowed for the gradual spread of some Mississippi-Great Lakes mussel species into eastern waters. Today in Vermont, seven mussel species are found only in the Lake Champlain Basin.

For more information on freshwater mussels in Vermont check out a new guide by Ethan Nedeau.