Freshwater mussels belong to the Family Unionidae and sometimes are called unionids. A mussel consists of two hard, oblong shells, made of calcium carbonate (limestone), that are held together by a hinge or ligament. Inside is a soft body made up of gills, a digestive tract, and tissue that produces the shell layer from dissolved minerals in the water. They move very slowly by way of a muscular foot, if disturbed. The age of a mussel can be counted by the layers of annual growth rings, just like the process of aging trees. Mussels are the longest lived of any freshwater invertebrate reaching ages of up to 70+ years. Mussels like to live in shallow, swift-moving water. They attach themselves to a rock or hard surface and filter water for food completely underwater. Their ability to filter water makes them very important for the environment because they clear suspended particles and toxins from our streams. Mussels are a very important food source for critters such as raccoons, fish, muskrats, ducks, herons, otters, and minks.
It is illegal to collect and/or sell any mussel species from Manassas National Battlefield Park. The Battlefield's species list of mussels was taken from Bull Run along the eastern edge of the park, Young's Branch, which flows through the center of the park, and Holkum's Branch, which flows through the southeastern end of the park in 1997. The origin of Bull Run starts just north of Prince William County, continues to flow southeast connecting with Black Branch, Chestnut Lick, Catharpin Run, Young's Branch, Holkum's Branch, and Pope's Head Creek. Bull Run flows along the southwestern edge of Hemlock Overlook Regional Park and Bull Run Regional Park. Bull Run joins the Occoquan River at Fountainhead Regional Park and continues into the Occoquan Reservoir. From there, the water flows into the Occoquan Bay, then into the Potomac River, then into the Chesapeake Bay, and finally into the Atlantic Ocean.
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The United States has over 300 species of mussels, which is the most diverse anywhere in the world. The greatest diversity of species is east of the Mississippi River. Still, some species have been reduced from millions to a few isolated populations. About 30 species are presumed extinct, about 60 are federally endangered or threatened, and about 70 species are listed as a special concern.
Historically, there were millions of mussels that inhabited the Ohio River basin (which includes the Huntington District of Virginia). Native Americans ate, traded, and made jewelry out of mussels. During the late 1880's up until the early 1900's, "pearling" was a popular Sunday event by settlers. Industry harvested pearly mussels from the streams to make buttons until about 1940. After WWII, dam building, siltation, industrial and sewage pollution, run-off from construction, development, mining, agriculture, and logging all collectively led to a serious decline in the number of mussels. The water was no longer swiftly moving in the channels. Siltation covered the hard objects mussels attach to and the mussels themselves, suffocating them. The leeched metals from the water started to become built up in the mussel's tissues, making them unfit to eat. Since the first part of the mussel life cycle is as a parasite on fish gills, the health of the fish populations is directly linked to the health of the mussel population. If native fish are eradicated by exotic species, acid rain, or any other disturbance, mussels will not be far behind.
Biologists use the mussel as a bioindicator species. They measure the amount of pollutant build-up in the mussel's tissues then determine the extent of water pollution. Researchers also are investigating certain characteristics of the mussel that are immune to cancer.