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Status: Endangered

Habitat: This mussel prefers clean, loose sand and gravel in medium to small rivers and streams. This mussel will bury itself in the bottom substrate to depths of up to four inches.

Behavior: Reproduction requires a stable, undisturbed habitat and a sufficient population of fish hosts to complete the mussel's larval development. When the male discharges sperm into the current, females downstream siphon in the sperm in to fertilize their eggs, which they store in their gill pouches until the larvae hatch. The females then expel the larvae. Those larvae which manage to attach themselves by means of tiny clasping valves to the gills of a host fish, grow into juveniles with shells of their own. At that point they detach from the host fish and settle into the streambed, ready for a long (possibly up to 50 years) life as an adult mussel.

Why It's Endangered: The clubshell was once found from Michigan to Alabama, and from Illinois to West Virginia. Extirpated from Alabama, Illinois and Tennessee, it occurs today in portions of only 12 streams. Reasons for its decline in the upper Ohio and Wabasha watersheds have been principally due to pollution from agricultural run-off and industrial wastes, and extensive impoundments for navigation. These are thought to be also responsible for its decline elsewhere as well.

An added threat now is the zebra mussel, a fast spreading exotic species accidentally introduced in ballast water from the Caspian Sea area. These tiny mussels reproduce in enormous numbers which tend to cover and suffocate native mussels.

November 1997

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