Synonyms

Elliptio dilatatus

  Basis for Listing

Historically widespread and locally abundant in Minnesota (Dawley 1947), the spike, also known as the lady finger, is now common only in the St. Croix River and its tributaries (Doolittle 1988; Havlik 1993), Rose Creek, and at the outlet of Lake Pepin on the Mississippi River (Hart 1999). Occasional specimens are collected from tributaries to the Mississippi River (Davis 1987), but it is apparently extirpated in the mainstem of the Minnesota River and its tributaries, despite ample habitat (Bright et al. 1990; Minnesota DNR, unpublished data). It has recently been found alive in only a small number of drainages, and degradation of its stream habitat is a continuing threat. For these reasons, the spike was listed as a special concern species in Minnesota in 1996.

  Description

The shell of the spike is elongate, moderately thick to heavy, compressed or slightly inflated, and up to 15 cm (6 in.) long. The outside of the shell is brown to black, occasionally with green rays. The beak sculpture consists of coarse loops raised slightly in the center. The pseudocardinal and lateral teeth are well-developed, and the inner shell is usually purple, sometimes white or orange, or a combination. The black sandshell (Ligumia recta) is similar, but is often heavily rayed and lacks beak sculpture.

  Habitat

Spike mussels are usually found in small to large rivers, but they are also known to inhabit reservoirs and lakes. Whether in rivers or lakes, they are most often found in sand and gravel substrates in depths ranging from 0.6-7.3 m (2-24 ft.) (Parmalee and Bogan 1998). When spike mussels do inhabit lakes or reservoirs, they are usually associated with outlet habitats dominated by swift currents.

  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. Survival rates for populations of spike mussels, much like other long-lived organisms, are high. Hart et al. (2001) reported that spike mussels have mean annual survival rates greater than 90%. These survival rates were measured in habitats colonized by zebra mussels (Dreissena polymorpha), and the survival rates in habitats without zebra mussels would most likely be even higher.

Mussels spend most of their lives buried in the bottom sediments of permanent water bodies, and often live in multi-species communities called mussel beds. They are primarily sedentary, but they can move around with the use of their foot, which is a hatchet shaped muscle that can be extended out between the valves (shells). A mussel will burrow its foot into the sediment and then contract it to pull itself slowly along the bottom of its aquatic habitat (Sietman 2003).

Mussels eat by filtering bacteria, protozoans, algae, and other organic matter out of the water. They draw water into their body through their incurrent siphon, remove food and oxygen with their gills, and then expel the filtered water through their excurrent siphon. Food particles are carried to the mussel's mouth by tiny hairlike cilia located on the gills. Waste is expelled through the excurrent siphon (Sietman 2003).

Mussels have a complex and distinctive reproductive cycle. Males release sperm into the water, which are drawn in by females through their incurrent siphon. Fertilized eggs are brooded in the female's gills, where they develop into tiny larvae called glochidia. The spike is a tachytictic breeder, with females brooding their young short-term, from May through August, before they are released as glochidia (Baker 1928). Once the glochidia are expelled from the female's gills, they attach to fish gills or fins by clamping onto them with their valves. The glochidia live as parasites on the host fish until they develop into juvenile mussels, at which point they detach from the fish and fall to the streambed as free-living mussels. Fish hosts for the glochidia of the spike mussel include the gizzard shad (Dorosoma cepedianum), flathead catfish (Pylodictis olivaris), white crappie (Pomoxis annularis), black crappie (P. nigromaculatus), and yellow perch (Perca flavescens) (Fuller 1974).

  Conservation / Management

Degradation of mussel habitat in streams throughout the spike's known range is a continuing threat. Spike populations in Minnesota are vulnerable to further decline because of hydrologic alteration of streams and their watersheds; the continuing decline in habitat conditions on the Mississippi River associated with its management as a navigation canal; and non-point and point source water pollution and sedimentation. Dams, channelization, and dredging increase siltation, physically alter habitat conditions, and block the movement of fish hosts. The spike mussel is also being impacted by the infestation of non-native zebra mussels 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. If current trends cannot be reversed, the spike may become threatened in the future. Further survey work in rivers where the spike mussel was formerly documented is needed to verify its status in that former range.

  Conservation Efforts in Minnesota

A 10-year statewide mussel survey initiated by the Minnesota DNR in 1999 resulted in a better understanding of the spike mussel's ecology and current status in Minnesota. A research project designed to measure the survival rate of a population of spike mussels is also ongoing in the Mississippi River (Hart 1999; Hart et al. 2001). Additionally, a small number of spikes were collected from zebra mussel infested habitats in the Mississippi River in 2000 and translocated into areas of the Mississippi River south of the Twin Cities, where habitats were devoid of zebra mussels.

  References and Additional Information

Baker, F. C. 1928. The fresh water mollusca of Wisconsin: part II: Pelecypoda. Wisconsin Geological and Natural History Survey Bulletin No. 70, Part II. University of Wisconsin, Madison. 495 pp.

Bright, R. C., C. Gatenby, D. Olson, and E. Plummer. 1990. A survey of the mussels of the Minnesota River, 1989. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 106 pp.

Davis, M. 1987. Freshwater mussels (Mollusca: Bivalvia: Unionidae) of the Cannon River drainage in southeastern Minnesota. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 21 pp. + figures and original data sheets.

Dawley, C. 1947. Distribution of aquatic mollusks in Minnesota. American Midland Naturalist 38:671-697.

Doolittle, T. C. J. 1988. Distribution and relative abundance of freshwater mussels in the Saint Croix National Scenic Riverway. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resouces. Unpaged.

Fuller, S. L. H. 1974. Clams and mussels (Mollusca: Bivalvia). Pages 215-273 in C. W. Hart, Jr., and S. L. H. Fuller, editors. Pollution Ecology of Freshwater Invertebrates. Academic Press, New York.

Hart, R. A. 1999. Population dynamics of unionid mussels in Lake Pepin, Upper Mississippi River, Minnesota and Wisconsin. Dissertation, North Dakota State University, Fargo, North Dakota. 162 pp.

Hart, R. A., M. Davis, J. W. Grier, and A. C. Miller. 2001. Survival of unionids following removal of attached zebra mussels. Journal of Freshwater Ecology 16(1):29-33.

Havlik, M. E. 1993. Unionids and margaritiferids (Mollusca: Bivalvia) in the Saint Croix River bordering Minnesota at Afton and Wild River State Parks, 8-17 June 1992. Final report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 41 pp.

Parmalee, P. W., and A. E. Bogan. 1998. The freshwater mussels of Tennessee. The University of Tennessee Press, Knoxville, Tennessee. 328 pp.

Sietman, B. E. 2003. Field guide to the freshwater mussels of Minnesota. Minnesota Department of Natural Resources, St. Paul, Minnesota. 144 pp.