Description: The Tar spinymussel, one of only three freshwater mussels in the world with spines, is a medium-sized mussel reaching about 2.5 inches in length. In young specimens, the shell’s outer surface (periostracum) is an orange-brown color with greenish rays; adults are darker with inconspicuous rays. The inside of the shell (nacre) is yellow or pinkish at one end and bluish-white at the other. Juveniles may have as many as 12 spines, however adult specimens tend to lose their spines as they mature. It’s found in association with other mussels, but it’s never very numerous. It feeds by siphoning and filtering small food particles suspended in the water.
The reproductive cycle of the species is similar to other native mussels. Males release sperm into the water, and the eggs are fertilized when the sperm are taken in by the females through their siphons during feeding and respiration. Females retain the fertilized eggs in their gills until the larvae (glochidia) fully develop. The glochidia are released into the water and must attach to the gills or fins of the appropriate fish species. They remain attached to their “fish host” for several weeks, drawing nourishment from the fish while they develop into juvenile mussels. They do not hurt their “fish host.” The juvenile mussels then detach from the fish host and drop to the bottom of the stream where they continue to develop, provided they land in a suitable place with good water conditions. This dependence on a certain species of fish increases the mussels’ vulnerability to habitat disturbances. If the fish host is driven off or eliminated because of habitat or water quality problems, the mussels can’t reproduce and will eventually die out.
Range: The Tar spinymussel likely once existed throughout much of the Tar River system. In the early 1980s, this spinymussel could be found relatively easily in the main stem of the Tar River in Edgecombe County, North Carolina. Presently, only two good populations are known to exist in two Tar River tributaries, while the species can only be found with great difficulty in one other tributary and in the main stem of the Tar River.
Critical habitat: None designated
Threats: The Tar River, like many other rivers, has been seriously degraded. Some of the Tar River has been dammed. Much of the river basin has been cleared for agriculture and other purposes, and poor erosion control on these lands allows large amounts of silt and sand to enter the river. This material smothers mussels and affects the stability of the river bottom. Discharges from agricultural, industrial, and domestic sources have also polluted much of the river system.
Why should we be concerned about the loss of species? Extinction is a natural process that has been occurring since long before the appearance of humans. Normally, new species develop, through a process know as speciation, at about the same rate than other species become extinct. However, because of air and water pollutions, forest clearing, loss of wetlands, and other man-induced environmental changes, extinctions are now occurring at a rate that far exceeds the speciation rate.
All living things are part of a complex and interconnected network. The removal of a single species cans set off a chain reaction that could affect many other species. For example, the loss of a single plant species can result in the disappearance of up to 30 other species of animals and plants. Each extinction diminishes the diversity and complexity of life on earth.
Species Contact:John Fridell
office - 828/258-3939, ext. 22
fax - 828/258-5330
160 Zillicoa St.
Asheville, NC 28801