While walking along one of the park's many waterside trails, you may notice large quantities of broken, discarded shells strewn about the shoreline and accumulating along the water bottom. This attests to the large populations of freshwater bivalves that inhabit the waterways of the George Washington Memorial parkway. These mussels are most frequently found partially buried in sandy gravel in slow moving sections of the river.
The wide distribution of our bivalves is due to their unique juvenile dispersal strategies and the relationships they maintain with native fishes. After fertilization, the mussel larvae develop within the gills of the parent mussel. This causes the mussel's gills to distend. (These elongated gills are termed "gill marsupia.") After a brief period of development. the larvae (called "glochidia") are released into the water column through the mussel's exhalent siphon. Then, the glochidia attempt to attach themselves to the gills of passing fish. Once attached, they derive sustenance from the blood plasma of their host until they complete their development. Then they drop off of the fish's gills and settle on the bottom. This relationship with native fishes allows mussels to distribute both upstream and downstream.
Bivalves feed by drawing water into their gills through their inhalant siphon. This is accomplished by rhythmically beating tiny hairs, or cilia, that line the labial palps near the mussel's internal mouth. The incoming water passes over the gills where tiny organic particles become trapped in a net of mucus strung between the gills. Beating cilia gradually draw the mucus-entangled food towards the mouth. By doing this shoals of mussels are capable of filtering large amounts of water, removing suspended particles, and improving water clarity.