USGS science for a changing world WHAT MAKES A HEALTHY ENVIRONMENT FOR NATIVE FRESHWATER MUSSELS? What are freshwater mussels, and what makes them special? Freshwater mussels are mollusks-close relatives of clams, oysters, and saltwater mussels. Many species of freshwater mussels can live for 20 to 30 years, and individuals of some species live for more than 100 years. Freshwater mussels have been valued by humans throughout history. They can produce pearls, and their shells can be used to make buttons for clothing or to serve as seedstock for Figure 1 . Life cycle of freshwater mussels. After fertilization of eggs (lower right corner), glochidia, or larvae, are released. Those glochidia that successfully attach to fish hosts transform into the cultured pearl industry. In past times, juvenile mussels, which detach and burrow into the streambed. (Diagram by G.T. Walters, Ohio freshwater mussels also were food for State University.) Native Americans. Attempts are being made to restore the stream bottom and along the edge of Freshwater mussels are sensitive to native-mussel populations in areas where water, especially if predators such as contamination of sediment that they reintroduction has a chance for success. muskrats, otters, and raccoons are feeding inhabit and to the water that they filter, The success of these attempts, however, in the area. making the presence of live, adult mus­ will depend on whether physical habitat sels an excellent indicator of ecosystem and other environmental factors are favor­ health and stability. Freshwater mussels able for the mussels to survive and repro­ What is the life cycle of are relatively immobile, imbedded in the duce. As yet, researchers and biological- freshwater mussels? streambed with part of their shell sticking resource managers know little about up into the water so that they can filter which environmental factors have the The life cycle of North American fresh­ water to obtain oxygen and food. This most significant effects on mussel com­ water mussels is unusual among aquatic lack of mobility makes them particularly munities or how various environmental animals because it usually requires fish as vulnerable to water and sediment contam­ factors interact to support or harm intermediate hosts for mussel larvae ination, changes in sedimentation, or pro­ mussels at various stages of life. (fig. 1). Freshwater mussels are conceived longed drought. Thus, ecosystem health when male mussels release sperm into the water and the eggs of nearby females are and stability are critical for their fertilized. The fertilized eggs of the reproduction and survival. Where are freshwater mussels found? female develop into larvae (glochidia), which are released into the water in ways Freshwater mussels are among the Although freshwater mussels are found that have evolved to attract host fish most endangered groups of animals in throughout much of the world, the highest (fig. 2). If a larva attaches to a fish, it will North America. Human influences such freshwater-mussel diversity on Earth is in ingest cell fluid of the fish for nutrition; as agricultural practices, construction of North America (Stansbery, 1970). For after a period of several hours to several dams, and urban sprawl have altered example, a single stream Big Darby weeks (depending on water temperature river flows, water quality, fish popula­ Creek, in central Ohio historically and species), the larva will transform to a tions, and other environmental factors contained 42 species of unionid mussels, juvenile, drop off the fish, and burrow that are essential for the survival of fresh­ more species than in all of Australia and into streambed sediment with its foot (fig. water mussels. These influences have Europe combined. Live freshwater mus­ 1). The proportion of released larvae that contributed to the continuing decline of sels are not often seen because they are actually attach to host fish and survive to freshwater mussels throughout the United partly buried in the sediments of creeks, inhabit the streambed is minute, estimated States (National Native Mussel rivers, and lakes. The empty shells of at anywhere from 1 in a million to 1 in Conservation Committee, 1998). dead mussels, however, can be found on 100 million (Waiters, 1995) U.S. Geological Survey USGS Fact Sheet 124-00 U.S. Department of the Interior October 2000 charge helps to moderate seasonal changes in streamflow and water temper­ ature, dilute contaminants in surface- water runoff, and help mussels survive drought. Base flow can be determined by analyzing long-term streamflow records, if available, and/or by making special streamflow measurements during a dry- weather period. Water and sediment quality. Because adult mussels are filter feeders, they are Figure 2. Female mussel displaying mantle to attract a fish host. Predator fish lured by the sensitive to waterborne contaminants prey-like appearance of the mantle come close to where glochidia are released, and some such as those carried in agricultural runoff glochidia may successfully attach. (Photo by G.T. Walters, Ohio State University.) and in municipal and industrial wastewa- ter. Juvenile mussels, on the other hand, What factors influence For example, the U.S. Geological may be particularly sensitive to the chem­ success during life stages Survey (USGS)-in cooperation with the istry of the sediments in which they live of freshwater mussels? U.S. Environmental Protection Agency, and feed. Thus, possible influences on Ohio Environmental Protection Agency mussel communities include not only the Each life stage for freshwater mussels has (Ohio EPA), Indiana Department of chemical quality of streamwater but also specific environmental requirements: Natural Resources (IDNR), Alien County the chemical quality of streambed sedi­ (Indiana) Soil and Water Conservation ments, which are particularly prone to Adults Adequate water quantity and District (SWCD), The Nature Conser­ storing trace metals and organic chemical quality, a stable stream channel, ade­ vancy, Ohio Department of Natural compounds. Water and sediment quality quate sediment quality, food, protec­ Resources (ODNR), and The Ohio State can be evaluated from a combination of tion from predators, and sufficient University did a study of this kind in the onsite measurements of water quality and population densities for fertilization. St. Joseph River Watershed in Indiana, collection of water and sediment samples Michigan, and Ohio. (See inset box for laboratory analyses. Larvae (Glochidia) Availability offish describing this study.) The purpose of this host upon which to attach, for study was to gather information on mus­ Stream-channel stability. A stable nourishment and dispersal. sel-population viability and suitability of stream channel is favorable for freshwater Juveniles Same as adults; however, stream sites for mussels, information that mussels because it provides a secure dwelling area and promotes water clarity. because a juvenile gathers food par­ could potentially help in efforts to restore In unstable channels, movement of stre­ ticles by extending its foot into the native-mussel populations in this water­ ambed sediment due to high flows often streambed, it is more sensitive to shed and perhaps elsewhere in the United leaves mussels either buried too deeply in sediment contamination than the States. Thirty-six species of freshwater adults that feed by filtering the mussels had previously been found in the sediment or stranded on sand or gravel bars, exposing the mussels to air and surrounding water. St. Joseph River Watershed, 30 of them occurring in Fish Creek, including the predators when streamflows are low. One approach toward clarifying the Federally endangered white catspaw Moreover, unstable channels are prone to relations between environmental factors (fig. 3), clubshell, and northern riffleshell producing excessive suspended sediment and healthy native-mussel communities is (Walters, 1988, 1995, 1998). A composite that can clog the mussels' gills (Strayer, to locate a particular stream where native- view of a site on Fish Creek is shown in mussel populations are known to exist, figure 4. then The following paragraphs list some compile an inventory of native fresh­ of the environmental factors that can be water-mussel species that have been studied; results from work in the St. found previously, Joseph Watershed are given in the inset section. follow with an evaluation of current populations, and Water quantity. For a particular stream collect data on possible positive and site or reach to be suitable habitat for negative factors contributing to the mussels, the stream bottom must not go Figure 3. Specimens of white catspaw mussel, Epio- survival of native freshwater dry. Thus, an adequate amount of base flow-that part of streamflow that is sus­ blasma obliquata perobliqua (Conrad, 1836). This mussels, using conventional water- very rare mussel species is on the Federal endan­ and sediment-quality analyses and tained by ground-water discharge to the gered species list. (Photo by G. T. Walters, Ohio ecological-assessment tools. stream-is crucial. Ground-water dis­ State University.) Figure 4. Composite view of surface and subsurface characteristics, Fish Creek near Alvarado, Ind. (site 8 on fig. 5). Environmental factors favorable for native freshwater mussels include a forested buffer along the streambanks and a gravel streambed with a moderate cover of silt. 1999a). Stream channels can be example, is native to Europe and Asia.