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Scaleshell Mussel (Leptodea leptodon)
Photo by Dr. M.C. Barnhart
The scaleshell is a freshwater mussel that was listed in 2001 as an endangered species by the U.S. Fish & Wildlife Service. Endangered species are animals and plants that are in danger of becoming extinct. Threatened species are animals and plants that are likely to become endangered in the foreseeable future. Identifying, protecting, and restoring endangered and threatened species is the primary objective of the US Fish and Wildlife Services endangered species program.
What is a Scaleshell Mussel?
Appearance - The scaleshell is a relatively small freshwater mussel with a thin, fragile shell and faint green rays. It grows to about one to four inches in length. The inside of the shell is pinkish white or light purple and highly iridescent. The scaleshell gets its name from the scaly appearance of the shell, which is only seen in females.
Range - Scaleshells historically occurred across most of the eastern United States. During the last 50 years this species became increasingly rare within a reduced range. Of the 55 historical populations, 14 remain scattered within the Mississippi River basin in Arkansas, Missouri, and Oklahoma.
Habitat - Scaleshell live in medium-sized and large rivers with stable channels and good water quality. They bury themselves in sand and gravel on the bottom with only the edge of their partially-opened shells exposed. As river currents flow over them, they siphon particles out of the water for food such as plant debris, plankton, and other microorganisms. The roles of scaleshell in river ecosystems are as food for wildlife like muskrats, otters, and raccoons and as filters which improve water quality.
Reproduction - The life cycle of the scaleshell, like most freshwater mussels, is unusual and complex. Their eggs develop into microscopic larvae (glochidia) within the gills of the female. The female discharges its glochidia into the river where they must attach to gills or fins of a fish to continue developing. Each mussel species has specific fish species (host fish) that are needed by the glochidia to develop. Freshwater drum have been identified as a host fish for the scaleshell but there may be other species. Glochidia continue growing on the fish and transform into juveniles. After a few weeks they drop off and land on the river bottom where they grow into adults.
What are the threats to the scaleshell mussel?
Pollution - Adult mussels are easily harmed by toxins and declines in water quality from pollution because they are sedentary (stay in one place). Pollution may come from specific, identifiable sources such as factories, sewage treatment plants and solid waste disposal sites or from diffuse sources like runoff from cultivated fields, pastures, cattle feedlots, poultry farms, mines, construction sites, private wastewater discharges, and road drainage. Contaminants reduce water quality and may directly kill mussels, reduce the ability of surviving mussels to have young, or result in poor health or disappearance of host fish.
Sedimentation - Sediment is material suspended in water that usually is moved as the result of erosion. Although sedimentation is a natural process, poor land use practices, dredging, impoundments, intensive timber harvesting, heavy recreational use, and other activities may accelerate erosion and increase sedimentation. A sudden or slow blanketing of the river bottom with sediment can suffocate freshwater mussels because it is difficult for them to move away from the threat. Increased sediment levels may also make it difficult for scaleshells to feed, which can lead to decreased growth, reproduction, and survival.
Dams - Dams affect both upstream and downstream mussel populations by disrupting natural flow patterns, scouring river bottoms, changing water temperatures, and eliminating habitat. The scaleshell, a mussel adapted to living in river currents, cannot survive in the still water impounded behind dams.
Scaleshells depend on their host fish as a means of moving upstream. Because dams are barriers that prevent fish from moving upstream they also prevent mussels from moving upstream. Upstream mussel populations then become isolated from downstream populations. This isolation leads to small unstable populations which are more likely to die out.
Exotic Species - The invasion of the exotic zebra mussel into the US poses a substantial threat, because it starves and suffocates native mussels by attaching to their shells in large numbers.
What Is Being Done to Prevent the Extinction of the Scaleshell?
Listing - The scaleshell was added to the U.S. List of Endangered and Threatened Wildlife and Plants on October 9, 2001, providing Endangered Species Act (ESA) protection. The ESA also requires that a Recovery Plan be prepared for listed species.
Watershed Protection Through Partnerships - The scaleshell cannot survive without soliciting outside help to restore habitat and improve surface lands. Causes of habitat degradation are numerous in streams throughout its range. In many cases, the threats are not from actions in or adjacent to the rivers where the species is found. Instead, threats are due to widespread problems originating on uplands at the highest elevations of watersheds. Habitat restoration will require improvements across the entire watershed. The voluntary assistance of Federal and State agencies, conservation groups, local governments, private landowners, industries, businesses, and farming communities will be necessary to meet recovery goals. The role of private landowners and businesses is important as land in watersheds occupied by scaleshell are primarily privately owned.
Recovery Plan - The US Fish and Wildlife Service prepared a recovery plan that describes actions needed to help the scaleshell survive. Some of these include: 1) stabilizing existing populations through artificial propagation; 2) utilizing existing legislation, regulations, and programs to protect remaining populations and habitat; 3) conduct research on critical aspects of its biology needed to manage the species and to identify harmful pollutants; 4) establish a recovery implementation team to apply sound science to recovery and foster partnerships; 5) work with willing partners to protect existing populations and habitat, eliminate threats, restore habitat, and improve surface land in watersheds, and 6) carry out an outreach and education to heighten awareness of scaleshell and to solicit outside help with recovery actions.
What Can I Do to Help Prevent the Extinction of Species?
Learn more about how the destruction of habitat leads to loss of endangered and threatened species and our nations plant and animal diversity. Discuss with others what you have learned.
Support local and State initiatives for watershed and water quality protection and improvement.
Help improve water quality locally in streams by minimizing use of lawn-care chemicals and properly disposing of or recycling hazardous materials found in your home, like batteries, paint, car oil, and pesticides.
Join a conservation group or volunteer at a local nature center, zoo, or wildlife refuge.
Last updated: April 14, 2015