Freshwater Mussels: World's Most Endangered


70% of No. America's Mussels Extinct or Endangered

The freshwater mussel Epioblasma triquetra, commonly known as the “Snuffbox”, is a member of the most endangered animal group in the world. Seventy-percent of North America’s freshwater mussels (referred to as “Unionids”) are already extinct or endangered. The genus Epioblasma used to consist of 25 distinct species, but 14 of those are now extinct. The remaining 11 species are either threatened with extinction or so poorly studied that their status is unknown.

Background
What is happening to our freshwater mussels, which were once so common they were able to support a thriving button industry, and served as an important food source for people? Unfortunately for this group, the majority need clean water with little silt load. Logging, river impoundments, agricultural run-off, shoreline development and other disturbances have largely eliminated the clean, swift-flowing currents that the Snuffbox and other freshwater mussels rely on.

The Snuffbox has a large range, from the Ohio River Valley west to the Mississippi and north to Wisconsin, Michigan and Ontario. But it is endangered throughout its range, occupying a spot on the endangered species lists not only federally but in Michigan, Wisconsin, Illinois, Indiana and Canada.

This small (2.5 inches), colorful (yellowish with dark rays and blotches) mussel has a fascinating lifestyle. Like all members of its genus, it uses a host fish to “grow” the larval glochidia. The glochidia reside in the gills of the fish, not feeding on the host but simply using it as relatively safe transport until the larva reaches maturity, when it drops to the river bottom and begins its life as an adult. In the case of the Snuffbox, the host fish is the Common Logperch, a small fish that is well known for using its snout to flip rocks and mussels in search of invertebrate food. But that rock flipping behavior makes them a perfect target for the female Snuffbox. She pokes a colorful, enlarged mantle out of her slightly opened shell, luring the Logperch in for a closer inspection. A mere 1/15 of a second elapses from the moment the fish touches the mantle until the mussel is clasped firmly over the fish’s mouth, pumping the glochidia into the mouth and gills of the host. Not exactly a mutually-agreed upon “host” situation!

The Snuffbox is currently the focus of several surveys and genetic studies designed to discover and enhance existing populations through conservation and reintroductions into appropriate rivers.

Prepared by Dr. David Zanatta, Central Michigan University. For more information on this research, please visit the homepage of Dr. David Zanatta at: http://www.cst.cmich.edu/users/zanat1d/dave_research.html.

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