New York Natural Heritage Program
Eastern Pondmussel
Ligumia nasuta (Say, 1817)
Bivalves

Threats [-]
The single most important cause of the decline of freshwater mussels during the last century is the destruction of their habitat by siltation, dredging, channelization, impoundments, and pollution. A healthy fish assemblage is critical to viable mussel populations and dams have resulted in heavy losses of mussels, mainly due to elimination of host fish species. Erosion due to deforestation, poor agricultural practices and the destruction of riparian zones, causes an increase in siltation and shifting substrates that can smother mussels. Domestic sewage, effluents from paper mills, tanneries, chemical industries and steel mills, acid mine runoff, heavy metals, and pesticides have all been implicated in the destruction of native mussel fauna. The zebra mussel invasion has dramatically lowered population numbers of this species, particularly in the lower Great Lakes basin (Metcalfe-Smith 1997). Owing to its thin shell, this species appears to be one of those most heavily affected by shell fouling by invasive zebra mussels. Unionids undergo tissue degrowth as a result of starvation, they become top-heavy, tip over and are unable to right themselves. Death is from starvation and complications arising from inproper orientation.

Conservation Strategies and Management Practices [-]
It may be difficult to control the impacts of established zebra mussel populations, but managers can work to prevent the spread of this invasive species to river systems and smaller lakes not yet invaded. The effects of PCB's and other toxic chemicals, and general water pollution, should be investigated for their potential role in the decline of this species. Ligumia nasuta had the highest body burden of PCB's among 6 different mussel species studied by Muncaster et al. (1990), possibly due to its small size. When feasible, the removal of impoundments in order to restore rivers to their natural flow would be beneficial since these structures negatively effect required fish host species as well as the mussels themselves.

Research Needs [-]
There is still much to learn about this species, especially determination of the host fish species. Details about habitat requirements (current speed, water depth, substrate grain size, substrate stability, water temperature, and water quality factors) also need work. However, Strayer et al. (1994) found that the distribution of Unionids was not related to these typical physical habitat qualities, but instead was related to long term stability of the substrate (i.e., flow refuges) and other large-scale habitat variables such as riparian zone vegetation (i.e., grassy vs. forested). Both large and smaller scale forces promoting the patchy occurrence of Unionid mussel beds is an active area of research (Strayer et al. 2004).