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Kingdom: Animalia
Division: Mollusca
Class: Bivalvia
Species Spotlight
[Photo: Noel Burkhead, U.S. Geological Survey]
Asiatic clam Corbicula fluminea
Description:A small light-colored mollusk with a hinged shell notable for distinct, concentric grooves and a rim with many fine notches. The shell is usually less than 38 mm wide.
Life History:Sexes are normally distinct; however, self-fertilizing hermaphrodites do exist. Spawning season commences in early summer, lasting for 6 months. Fertilization occurs in inner gills; larvae are released when they grow to a size of 1 mm.
Habitat:Found in most major waterways in the U.S., Asiatic clams are filter feeders that remove particles from the water column. They can be found at the sediment surface or slightly buried.
What is a Bivalve?
Bivalves are members of the taxonomic class Bivalvia, including freshwater clams and mussels. Bivavles' soft bodies are protected by two hard shells (valves) joined by a flexible hinge. Opening the hinged valves permits the animal to filter water and capture microscopic food items like bacteria, debris, and plankton (Pennak 1989).
Bivalve Habitat
Most common in larger rivers, freshwater bivalves are found in virtually all North American freshwater ecosystems. Their life history includes a parasitic larval stage infesting the gills of a host fish. As adults, freshwater bivalves use a muscular "foot" to secure themselves in mud or gravel river bottoms where they filter water for food.
Ecological Importance of Bivalves
A single bivalve filters many gallons of water per day, purifying water of harmful microorganisms like E. coli and blue-green algae. High numbers of bivalves improve water quality by filtering these contaminants (USGS 2000). As prey items, bivalves are eaten by predatory fish, mammals, waterfowl, crayfish, turtles, frogs, and aquatic salamanders (McMahon 1991). Freshwater bivalves are hosts for parasites like flukes, worms, and water mites of the family Unionicolidae.
Bivalve Sensitivity to Water Quality Degradation
Bivalves are at risk from water quality degradation due to a combination of factors. First, their inability to move away from pollution and the volume of water they filter daily increases their exposure to chemical wastes, heavy metals, urban wastewater and sediment pollution, and industrial effluents (Last & Whitman, 1999). Second, Bivalves are unable to move when their habitat is disturbed by dredging or construction of dams. Finally, loss of host freshwater fishes can reduce bivalves' reproductive success. Non-native bivalves are often more tolerant of pollution (Fuller 1974).
For more about bivalves, see the Web resources for freshwater bivalves on this page.
