The Eastern Pondmussel… a Species at Risk

This species has been identified as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and is listed under the federal Species at Risk Act (SARA). Under the SARA, a recovery strategy must be developed for this species.

General Description

Ligumia nasuta

Photo by National Water Research Institute 

The Eastern Pondmussel (Ligumia nasuta) was once among the most common species of freshwater mussels in the lower Great Lakes. It is a member of the family Unionidae and has the following characteristics:

• Medium to large in size (average 70 mm) with a long, elliptical, compressed shell;
• Shell is thin but strong;
• Posterior ridge is well-developed, distinct and angled near the beak; posterior end is bluntly pointed;
• Anterior end is rounded; ventral margin broadly curved;
• Females have a swelling along the posterior ventral margin; lacking in males;
• Beaks are located in the anterior quarter of the shell and are low and slightly raised above the hinge line;
• Shell surface is rough with concentric wrinkles and visible lines of growth;
• Shell colour of juveniles is yellowish or greenish black with narrow green rays at posterior end;
• Shell of adults is dark brown or black; and
• Nacre is often silvery white or bluish white.

Distribution

The range of the Eastern Pondmussel is limited to eastern North America from the lower Great Lakes to New York, New Hampshire and in coastal rivers to South Carolina. In Canada, only two populations are believed to exist; in the delta area of Lake St. Clair (in the transition zone between wetlands and open water) and in a small tributary of the upper St. Lawrence River, Lyn Creek, near the outlet of Lake Ontario. It is believed that the Eastern Pondmussel has been lost from over 90% of its historical range in Canada.

Eastern Pondmussel Distribution

Habitat and Life History

The preferred habitat of the Eastern Pondmussel is sheltered areas of lakes or slow streams in substrates of fine sand and mud at depths up to 4.5 m. During spawning, males release sperm into the water and females siphon it out of the water and filter it with their gills. In the late summer, the female eggs are fertilized in a special area of the gill (marsupium) where they develop into larvae (glochidia). Once released the following spring, glochidia require a suitable host (most often a fish) on which they become encysted and feed. They remain on the host until they develop into juveniles, at which time they drop off and bury in the sediment. They remain buried until sexual maturity, estimated to be between 6 and 12 years.

Hosts

Glochidial hosts for this mussel are not specifically known. Its presence in Atlantic coastal rivers suggests that at least one host is tolerant of brackish water.

Diet

The Eastern Pondmussel is a filter-feeder. Adults consume bacteria, algae and particulate matter from the water. Juveniles feed on similar food; however, because they live entirely buried in the sediment, their food is obtained directly from the sediment and pore water.

Threats

The most important threat to the Eastern Pondmussel is the Zebra Mussel (Dreissena polymorpha). Since the mid-1980s, over 90% of the area once occupied by the Eastern Pondmussel has become infested with Zebra Mussels. In addition, lowered water levels resulting from climate change are expected to decrease available habitat.

Similar Species

Similar species include Elliptio complanata, E. dilatata and Ligumia recta.

Text Sources: COSEWIC Status Report 2007.

For more information, visit the SARA Registry Website at www.SARAregistry.gc.ca.