Simpsonaias ambigua (Say, 1825)
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Basis for Listing
The salamander mussel is a widespread species in the Mississippi and Ohio river drainages, but one that is uncommon and rarely collected (Mathiak 1979; Oesch 1984; Clark 1985; Parmalee and Bogan 1998). In Minnesota, the salamander mussel historically occurred in the Mississippi River (based on the presence of a single relic shell at Hastings) but it is currently restricted to the lower St. Croix River, where it is rare. Given its limited distribution and narrow habitat requirements, the salamander mussel was listed as a threatened species in Minnesota in 1996.
The shell of the salamander mussel is elongate or oblong, with thin valves, and it reaches up to 5 cm (2 in.) long. The beak is raised slightly above the hinge line, and the beak sculpture consists of several thin ridges raised in the middle, forming an upside down V. The outside of the shell is yellowish-tan to dark brown, and rayless. The teeth are rudimentary, almost unnoticeable, with 1 small, thin pseudocardinal tooth present in each valve. The lateral teeth are absent, and the inner shell is whitish. The salamander mussel can be distinguished from the cylindrical papershell (Anodontoides ferussacianus) and the spectaclecase (Cumberlandia monodonta) by its teeth characteristics and beak sculpture.
The salamander mussel is very habitat specific, living only under flat rocks (Clark 1985) or under ledges of rock walls (D. Heath, Wisconsin DNR, pers. comm.), habitats also occupied by its glochidial host, the mudpuppy salamander (Necturus masculosus) (Howard 1915).
Biology / Life History
Mussels are long-lived animals. Members of many species may live for several decades and in some instances, a century or more. They spend most of their lives buried in the bottom sediments of permanent water bodies, and often live in multi-species communities called mussel beds (Sietman 2003).
Conservation / Management
Factors that potentially threaten the continued existence of the salamander mussel include high stream-flow variations on the St. Croix River caused by a hydroelectric dam operating on a seasonal peaking regime, and the threat of non-point and point source water and sediment pollution (U.S. Fish and Wildlife Service 1997). Dams, channelization, and dredging increase siltation and physically alter habitat conditions. The salamander mussel is also being impacted by the infestation of non-native zebra mussels (Dreissena polymorpha) in the Mississippi River and its tributaries. Zebra mussels can attach themselves in large numbers to the shells of native mussels, eventually causing death by suffocation.
Conservation Efforts in Minnesota
A 10-year statewide mussel survey initiated by the Minnesota DNR in 1999 resulted in a better understanding of the salamander mussel's ecology and current status in Minnesota.