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42 OVERVIEW OF RIVER-FLOODPLAIN ECOLOGY IN THE UPPER MISSISSIPPI RIVER BASIN Van der Schalies' oversight of other late 1800's mussel investigations and more recent mussel studies. To evaluate temporal changes in the UMR mussel fauna, Fuller (1980) compared the abundance of mussel species in data collected by historical investigators with data he collected in a 1977 survey. According to Fuller (1980), four species have not been collected since about 1930 and a total of five since around 1900. Those five were Tritigonia verrucosa, Potami/us capax. Venustaconcha ellipsiformis, Alasmidonta marginata, and Simpsoniconcha amhigua. even though S. amhigua has been collected more recently at three UMR locations. Although the actual number of mussel species has not declined significantly since 1900, the abundance of certain mussel fauna has changed drastically. The most docu- mented case is that of the ebony shell (Fusconaia ehena), which was once so abundant that it made up 80 percent of the commercial shell industry (Coker, 1919). The ebony shell depends upon the skipjack hening as the host fish for part of its reproductive cycle. With the construction of the hydroelectric dam at Keokuk, Iowa, in 1913, the skipjack herring could no longer make spawning runs upriver and serve as the host fish for ebony shell glochidia. The ebony shell is still present but represented only by extremely old individuals and thus is likely to disappear from the UMR. The elephant ear (Elliptio crassidens) is in a similar situation. A cursory examination of the community composition reveals that, historically, many species probably made up only a small fraction of the original mussel assemblage. In his examination of Ellis' (1931) survey, Fuller (1980) noted that approximately two-fifths of the mussel species made up less than I percent of the mussel population. The decline in less common species was more evident in Fuller's 1977 sur- vey (Fuller, 1978), which found that approximately one-half of the species group mussel taxa made up less than I per- cent of the fauna. Two species (Amhlema plicata and Trun- cilia truncata) made up 48.88 percent of all the specimens collected. Only 16 species showed some degree of stability over the 50 years between Fuller's survey and that of Ellis (1931). Lampsilis teres made up 13.8 percent of the popula- tion in Ellis' survey but only 0.23 percent of Fuller's, and Leptodea tragi/is similarly declined from 10.1 to 1.27 percent. Proptera alatus declined from 3.75 to 1.38 percent. Fuller (1980) suggested that the decline of some species (such as P. alatus) could reduce substrates (relict shells) used by invertebrates (Le" aquatic insects) that serve as food for other organisms. Some species have increased in abundance but as a result of negative changes caused by navigation improve- ments. Truncilla donaciformis made up only 3.1 percent of Ellis' collection but was the second most abundant in Fuller's survey at 14.2 percent. Fuller theorized that T. donaciformis populations were relatively low in the 1930's because the preferred habitat was found on dynamic substrates that were eliminated as the riverbed meandered. When more stable (less dynamic) backwaters were created through navigation development, the species population increased. Comparison of the results of the Ellis survey with those of Fuller's survey perfonned for the U.S. Anny Corps of Engineers clearly shows that certain distinct alterations impacted the mussel fauna during the intervening period of about 50 years (Fuller, 1978). Although Potamilus capax and Lampsilis higginsi have been listed as federally endan- gered species. other species such as E/liptio crassidens are equally as rare. Fuller (1980) described 50 UMR species on the basis of their apparent health. Although admittedly sub- jective, Fuller categorized 2 taxa as endangered, 21 jeopar- dized, 12 troubled, and only 15 as healthy. Endangered species were defined as taxa of a nationally protected spe- cies group that are in danger of extinction throughout much or all of their natural range. Jeopardized mussels face extir- pation in the UMR for one or more reasons. including com- mercial harvest, declining water quality, impoundment (especially streambed change), and lack of suitable hosts. Troubled species are those whose historical quantity and (or) geographic range in the UMR have been reduced, but each exhibits some evidence of reproduction. Fuller (1980) attributed the decline of the mussel fauna to five factors: waterway modification, streambed change, commercial har- vest, declining water quality, and the Asiatic clam. Several species that were marginally suited to the UMR declined because they were unable to adapt to a mul- titude of changes. Other species grew in abundance and (or) dominance because of these changes. Overall, the number of mussel species in the UMR assemblage has declined in the last 50 years. About the same time that Fuller was doing work on UMR mussels, another survey of river union ids was being perfonned by Perry (1979) for the Upper Mississippi River Conservation Committee (UMRCC). Perry's survey was more qualitative than those surveys perfonned by Grier and Mueller (1922-1923), Van der Schalie and Van der Schalie (1950), and Fuller (1980). Although Perry collected no har- vest data, his findings of the species composition are similar to Fuller's. Perry described 13 of the species collected as common, compared with Fuller's description of only 15 species as "healthy." Perry's description of factors contrib- uting to the decline of mussel species agreed with that of Fuller. The previous discussion focused on changes to the spe- cies composition of UMR mussel fauna. Little discussion has been devoted to changes in the population related to commercial harvest. Beginning about 1889, mussels were harvested for their freshwater pearls and to make buttons for the gannent industry. Like the gold rush, a frenzied search began that resulted in an estimated $300,000 worth of pearls being found by 1891 (O'Hara, 1980). Since freshwater pearls are relatively rare, this search required the collection