Eastern Pondmussel
Sagittunio nasutus (formerly: Ligumia nasuta)
Species Description
A medium-sized freshwater mussel that reaches an average length of 7cm, the Eastern Pondmussel is defined by its long, slender shell that is bluntly pointed at the posterior end. The colour of their shells varies from yellowish to greenish black in younger individuals, often becoming darker with age. Narrow green rays that are concentrated at the posterior end are sometimes visible in light-coloured individuals.
Lifecycle
The truly fascinating life history of the Eastern Pondmussel is revealed when reproducing females use their lure to attract host fish. Females open their shell to display their mantle with small white papiliae that they ripple up and down to mimic a swimming amphipod, a shrimp-like crustacean that is a favoured prey item for many fish. When a fish strikes this lure, larvae known as glochidia are released and attach to the gills of the fish where they absorb nutrients and metamorphose over several weeks, then detach and float down to the substrate as a juvenile mussel.
Host fish species of the Eastern Pondmussel are believed to include Brook Stickleback, Largemouth Bass, Pumpkinseed and Yellow Perch.
Eastern Pondmussels play an integral role within an ecosystem. They filter water, removing algae, organic matter, and bacteria, which helps to clean and improve the clarity of water benefiting the health of the aquatic environment, people, and other aquatic organisms like plants, fishes, and invertebrates. Eastern Pondmussels are sensitive indicators for the overall health of a freshwater system including the fish community, which they depend on for successful reproduction.
Habitat
The slow-moving waters and soft sandy or muddy substrate of ponds, lakes, coastal wetlands, sheltered bays, and quiet waters of large rivers are the preferred habitats of the Eastern Pondmussel, however, these habitat types are some of the most imperiled in Ontario.
Distribution
The Eastern Pondmussel is native to eastern North America in freshwaters of the lower Great Lakes and coastal rivers along the Atlantic. Prior to 1990, the Eastern Pondmussel was the fourth most common mussel species in Ontario’s lower Great Lakes region.
As a result of the introduction and spread of Zebra and Quagga mussels in the late 1980s, the Eastern Pondmussel has been lost from offshore areas in Lake St. Clair and Lake Erie. Although the species has been lost from much of its historical range, a refuge for Eastern Pondmussel persists in nearshore areas of the St. Clair River Delta in Bkejwanong Territory, which is protected and managed by Walpole Island First Nation who are contributing to the recovery efforts for this species.
In Ontario, Eastern Pondmussels are still found in the St. Clair River Delta and coastal wetlands of Lake Erie and Lake Ontario. They are also found in some inland lakes in eastern Ontario and a tributary of the upper St. Lawrence River. There is only one record of an Eastern Pondmussel in the Sydenham River near Alvinston from 1992.
Threats to the Eastern Pondmussel
The largest threats to the Eastern Pondmussel are invasive species and poor water quality. Zebra and Quagga mussels have contributed significantly to declining numbers of the Eastern Pondmussel in the lower Great Lakes basin. Invasive Phragmites australis (European Common Reed) is another non-native species that has impacted Eastern Pondmussel populations as it outcompetes native vegetation and forms dense stands that reduce the quality and availability of habitat needed by these mussels such as coastal wetlands.
Eastern Pondmussels are also threatened by aquatic pollution from wastewater, agricultural, and industrial effluents as well as road salt. High levels of sediment-born contaminants and toxic substances absorbed during filter feeding can result in mortality. Juveniles are particularly sensitive to even low concentrations of heavy metals, ammonia, and changes to salinity and acidity. Increases in turbidity and sediment loading can also suffocate mussels and because many mussel species rely on visual displays to reproduce, any significant reduction in water clarity can disrupt their life cycle.