The Freshwater Mussels (Mollusca: Bivalvia: Unionoida) of Nebraska
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Transactions of the Nebraska Academy of Sciences and Affiliated Societies Nebraska Academy of Sciences 11-2011 The Freshwater Mussels (Mollusca: Bivalvia: Unionoida) of Nebraska Ellet Hoke Midwest Malacology, Inc., ellethoke@charter.net Follow this and additional works at: https://digitalcommons.unl.edu/tnas Part of the Life Sciences Commons Hoke, Ellet, "The Freshwater Mussels (Mollusca: Bivalvia: Unionoida) of Nebraska" (2011). Transactions of the Nebraska Academy of Sciences and Affiliated Societies. 2. https://digitalcommons.unl.edu/tnas/2 This Article is brought to you for free and open access by the Nebraska Academy of Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Transactions of the Nebraska Academy of Sciences and Affiliated Societiesy b an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. The Freshwater Mussels (Mollusca: Bivalvia: Unionoida) Of Nebraska Ellet Hoke Midwest Malacology, Inc. Correspondence: Ellet Hoke, 1878 Ridgeview Circle Drive, Manchester, MO 63021 ellethoke@charter.net 636-391-9459 This paper reports the results of the first statewide survey of the freshwater mussels of Nebraska. Survey goals were: (1) to document current distributions through collection of recent shells; (2) to document former distributions through collection of relict shells and examination of museum collections; (3) to identify changes in distribution; (4) to identify the primary natural and anthropomorphic factors impacting unionids; and (5) to develop a model to explain the documented distributions. The survey confirmed 30 unionid species and the exotic Corbicula fluminea for the state, and museum vouchers documented one additional unionid species. Analysis of museum records and an extensive literature search coupled with research in adjacent states identified 13 additional unionid species with known distributions near the Nebraska border. Some of these unionids may have formerly inhabited the state. Seven documented species have probably been extirpated, and the ranges of 15 others have contracted significantly. Only nine species are relatively stable at present, and one of these is extremely rare and feder- ally endangered. Diversity is concentrated in the formerly glaciated portion of eastern Nebraska, and drops abruptly along the Missouri River to the east and in the Great Plains westward. The primary natural factors influencing unionid distributions in Nebraska include availability of perennially flowing waters, host fish diversity, substrate composition and stability, and formerly heavy sediment loads. Anthropomorphic factors are surface and subsurface irrigation withdrawals, construction of canals and reservoirs, channelization, erosion, intensive grazing, contaminants, and the introduction of invasive species. Unionid presence and diversity largely correlates with substrate stability. Stream orientation and morphology in portions of eastern Nebraska promote slow currents, and substrates composed of mud, sand, and rock provide greater stability than the shifting sand substrates common elsewhere in the state. In central and western Nebraska, unionid populations are concen- trated in headwaters, backwaters, and side-channels of rivers, and canals, reservoirs, and small tributaries, while the generally shifting sand habitats of most rivers provide relatively little viable habitat. In the historic Missouri River, unstable substrates and (formerly) heavy sediment loads limited diversity to silt tolerant species, and viable habitat largely to backwaters, sloughs, attached lakes, side channels, and relatively few main channel environments. Today, upstream dams have greatly reduced the sediment load in the Missouri River, but unstable substrates restrict mussels to backwaters, side channels, pools below wing dams, revetments, and other areas sheltered from strong currents. Channelization and erosion/sedimentation have destroyed or drastically impacted stream habitats in eastern Nebraska resulting in the loss of much of the original unionid diversity. Surface and subsurface irrigation coupled with related declines in water tables have eliminated habitat in western Nebraska, though losses are partially compensated for some species by colonization of viable reaches of newly created impoundments and canals. Intensive grazing along streams and agricultural pollution further exacerbate habitat deg- radation and pressure remaining unionid populations. Invasive species directly compete with native mussels for sustenance and living space and may become serious threats to the survival of remaining unionid species in some habitats. Introduction The greatest unionoid diversity in the world is in Research on Nebraska mussels did not benefit North America (Bogan, 1993). The eastern, midwestern directly from the flow of money into the field in the and southern United States contain the greatest early 1900’s propelled by commercial interest in diversity and populations of mussels, and are also the mussels relating to the button industry. In 1900 there regions that have received the majority of attention, was one button manufacturer in Nebraska and two scientific and otherwise. Investigations in the Missouri by 1905 (Wilson, 1910), however, Coker (1919) does River Basin from the Kansas River northward were not include Nebraska in his list of states where “the minimal until the last quarter of the twentieth century. mussel fishery is pursued more or less actively.” In Nebraska during the nineteenth and most of the The extent of research in adjacent states at the twentieth centuries, research on mussels was largely initiation of this study was similarly limited. In limited to reports of their existence (William Clarke - Kansas, Murray and Leonard (1962) listed only a few 1804 as cited in Moulton, 2003), a few isolated species occurring north of the Kansas River. The latest collections (Lea, 1858; Hayden, 1862; Tryon, 1868; research in Missouri was that of Utterback (1914, 1915- Walker, 1906; Canfield and Wiebe, 1931), and a small 16, 1917), and in South Dakota, the most recent number of museum vouchers often with only general publication was that of Over (1942). Little was known locational data (i.e. state, river). The most extensive of the mussels of western Iowa (Keyes, 1888; Bovbjerg publication on the unionoids of Nebraska was that of et al. 1970), and the Missouri River was reported to be Aughey (1877), however, aspersions on his academic devoid of molluscan life below the confluence of the reputation as well as questions on the accuracy of his Milk River in eastern Montana (Hayden, 1862; identifications preclude reliance on that paper (Bolick, Utterback, 1914, 1915-1916, 1917; Coker and Southall, 1993; Hoke, 2000b). 1915; Over, 1915, 1942; Bartsch, 1916). 2011 Transactions of the Nebraska Academy of Sciences 32, 1–46 1 E. Hoke The general absence of research on Nebraska The unionoid reproductive cycle is susceptible to unionids in 1972 suggested the need for a statewide interruption at many points. For example, elimination survey, and this study was initiated at that time. The of the host fish will, over time, result in the elimination goals of the study were: (1) to document existing of dependent species of freshwater mussels. Similarly, distributions through a statewide survey of living displacement of the host fish from the immediate and recent shell materials; (2) to document the extent vicinity of female mussels during the breeding period of past distributions through collection of relict can produce the same effect. Different species of specimens and by searching museums for relevant mussels have evolved a number of methods to achieve vouchers; (3) to identify changes in the fauna through infection of host fish. There are two distinct levels to comparison of distributions revealed by recent and this problem: (1) attraction of a suitable host fish to the relict shells; (4) to identify and understand the immediate vicinity of the female mussel, and (2) primary factors influencing past and present successful infection of the host with glochidia. Some distributions; and (5) to develop a model to account mussels solve both problems by one method: for changes in the fauna through time. broadcast dispersal of thousands of glochidia into the Before discussing the survey, it is necessary to water column. Many unionoid species produce briefly comment on the subjects of unionoid biology, conglutinates, worm-like structures filled with and the physical and aquatic geography of Nebraska. glochidia, that resemble one of the foods in the host A basic familiarity with these subjects is useful to fish’s diet. In eating the conglutinate, the fish becomes fully understand the sections that follow. infected with glochidia. Some fish species utilize thin- shelled mussels for food, and in the process of Unionoid Biology and Life History obtaining nourishment, may be infected with Freshwater mussels are the most imperiled faunal glochidia. There are many other strategies to attract group in North America (Williams et al. 1992) with and infect host fish including lures (Kraemer, 1970), 213 of the 297 known taxa considered to be extinct, mucus nets (Watters and O’Dee, 1997), and assembly endangered, threatened or of special concern. The of a glochidia filled structure, a superconglutinate, current condition of the fauna reflects the extent of resembling a fish used by the host as a primary food