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New Record for the Freshwater Snail Lithasia geniculata (Gastropoda: Pleuroceridae) in the Ohio River, IL, with Comments on Potential Threats to the Population
Jeremy S. Tiemann and Kevin S. Cummings

Southeastern Naturalist, Volume 9, Issue 1 (2010): 171–176

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New Record for the Freshwater Snail Lithasia geniculata (Gastropoda: Pleuroceridae) in the Ohio River, IL, with Comments on Potential Threats to the Population Jeremy S. Tiemann1,* and Kevin S. Cummings1 Abstract - We report on a recently discovered population of the freshwater snail Lithasia geniculata (Ornate Rocksnail) (Gastropoda: Pleuroceridae) from the Ohio River, IL, the first documented occurrence for this species outside the Tennessee and Cumberland river basins. We collected 14 individuals on 26–27 August 2008 from the Ohio River, near Mound City, Pulaski County, IL. All of the specimens collected were discovered on an exposed shoal after the river dropped ≈0.5 m in a 24-hr period and had several (7–33) Dreissena polymorpha (Zebra Mussel) attached to their shells. Freshwater snails (Gastropoda) are a vital component of many stream ecosystems. Not only does their sensitivity to perturbations allow them to be used as biological indicators of stream integrity, but they also occupy a central position in food webs by grazing on periphyton and providing a food source for predators (Brown et al. 2008). The family Pleuroceridae, a group of gill-breathing, operculate snails, reaches its greatest diversity in streams of the southeastern United States (Brown et al. 2008, Burch 1989, Minton and Lydeard 2003). Within North America, the group is composed of 7 genera and approximately 156 species, but has experienced a severe decline in diversity during the past century (Brown et al. 2008, Burch 1989, Graf 2001, Minton and Lydeard 2003, Turgeon et al. 1998). The entire genus Gyrotoma (6 species), endemic to the shoals of the Coosa River, Alabama–Georgia, and approximately 26 other species in the family are now presumed globally extinct due to inundation of riffl e areas by impoundments and habitat degradation from poor land-use practices (Brown et al. 2008, Burch 1989, Lysne et al. 2008). The 32 extinct species plus the 5 that are on the federal endangered species list comprise roughly 20% of the known North American pleurocerid fauna. Freshwater gastropods remain an understudied fauna, and disseminating research findings (e.g., distribution and status records) so that all parties have access to the most up-to-date information is an important factor in snail conservation (Brown et al. 2008, Lysne et al. 2008, Perez and Milton 2008). Illinois is on the northwestern edge of the range of many pleurocerids, but little is known about the group in the state (Cummings 1991). The last to compile information on the distribution and status of the family in Illinois was Baker (1906). In Illinois, 8 of the 11 pleurocerid species are found only in the Wabash/Ohio River basin (Baker 1906, Burch 1989, Cummings 1991). We have begun investigating the status of pleurocerids of Illinois by conducting literature reviews (e.g., Burch 1989, Goodrich 1940, 1941), examining museum specimens and data (e.g., Carnegie Museum of Natural History, Pittsburgh, PA [CM]; Chicago Academy of Science, Chicago, IL [CA]; Field Museum of Natural History, Chicago, IL [FMNH]; Florida Museum of Natural History, Gainesville, FL [UF]; the now combined Illinois Natural History Survey [INHS] and University of Illinois Museum of Natural History [UIMNH], Champaign, IL; Ohio State University Museum, Columbus, OH [OSUM]; and University of Michigan Museum of Zoology, Ann Arbor, MI [UMMZ]; acronyms follow Leviton et al. 1985, except for Ohio State), and qualitatively collecting snails throughout the state. While conducting surveys of the Ohio River, we found an undocumented population of Lithasia geniculata Haldeman (Ornate Rocksnail) (Fig. 1) and herein report about it and potential threats to the population. Notes of the Southeastern Nat u ral ist, Issue 9/1, 2010 171 172 Southeastern Naturalist Notes Vol. 9, No. 1 We conducted turtle and qualitative snail surveys in the Ohio River downstream of Metropolis, IL, on 25–27 August 2008. While checking turtle traps near Mound City, Pulaski County on the 26th, we noticed the river had dropped approximately 0.5 m from the previous day. This drop in water level exposed a shoal that was not sampled on the 25th. We sampled the shoal for 0.5 person-hours on the 26th and 0.75 person-hours on the 27th. Fourteen live individuals of L. geniculata were collected during the 2-d period and were found in sandy areas with small amounts of gravel. The exposed pools on the shoals were large, and numerous individuals were observed but not collected; in addition, not all of the exposed pools were sampled. Individuals collected were preserved in 95% EtOH and deposited into the Illinois Natural History Survey Mollusk Collection, Champaign (INHS 32740). The 14 vouchered individuals varied in height from 17–25 mm (mean 21.1 ± 2.3 mm SD). Although L. geniculata can be phenotypically variable (Minton et al. 2008), the specimens we collected were distinctly shouldered with a single crown-like row of nodules on the upper portion of the body whorl (Fig. 1), typical of L. geniculata (Branson 1987, Goodrich 1941). Prior to our survey, the only published records of L. geniculata (= L. geniculata geniculata and L. geniculata fuliginosa) were from the Tennessee River drainage (e.g., the mainstem Tennessee River and Duck River basin) in Kentucky, Tennessee, Figure 1. Lithasia geniculata (Ornate Rocksnail) from the Ohio River, Mound City, Pulaski County, IL (INHS 32740). The specimen (24 mm in height) had 32 Zebra Mussels removed for identification purposes. 2010 Southeastern Naturalist Notes 173 and Alabama, and the Cumberland River drainage (e.g., the mainstem Cumberland River and Red River basin) in Kentucky and Tennessee (Burch 1989, Gooch et al. 1979, Goodrich 1940, Minton 2002, Minton and Lydeard 2003). The closest populations of L. geniculata to the one we discovered appears to be in the Tennessee River downstream of Kentucky Lake at river mile 5.3 (Gooch et al. 1979), and in the Cumberland River downstream of Lake Barkley near river mile 9 (J. Sickel, Murray State University, Murray, KY, pers. comm.; INHS 33096). Our discovery expands the known range of L. geniculata into a new basin (Ohio River), a new state (Illinois), and documents its occurrence in the lower Cumberland River (Fig. 2). We did, however, encounter additional specimens in our museum search referable to L. geniculata from the Falls of the Ohio River, near Louisville, KY, collected in 1904 (FMNH 80314). OSUM has two lots from the Ohio River that are referable to L. geniculata: 22 miles upstream of Louisville collected by C. Stein in 1961 (OSUM 14378), and 10 river miles upstream of Louisville collected by Greenwood and Thorp in 1989 (OSUM 19823). Although the OSUM specimens were initially identified as Lithasia obovata (Say) (Shawnee Rocksnail), they were distinctly shouldered but lacked a definite row of nodules. Minton et al. (2008) suggested that Lithasia spp. can contain Figure 2. Distribution of Lithasia geniculata (Ornate Rocksnail). Triangle indicates where the Ohio River, IL, specimen was found, and circles indicate where the species was known prior to our survey. Historical information (= L. geniculata geniculata and L. geniculata fuliginosa) obtained through Gooch et al. (1979) and specimens located at CA, CM, FMNH, INHS (including UIMNH), OSUM, UF, and UMMZ. 174 Southeastern Naturalist Notes Vol. 9, No. 1 substantial intraspecific variation in shell form. We believe that such ecophenotypic plasticity might help to explain the morphological form found in the upper Ohio River. It seems doubtful that the Ohio River individuals were deliberately discarded through human activity. We know of no published studies documenting snail transport on barges or boats, nor do we know of any aquatic organisms (e.g., macrophytes) transported from Tennessee to the Ohio River. Furthermore, pleurocerids are not a component of the pet or bait trade. We also think it is improbable that the snails washed or moved downstream from extant populations upstream because of the lack of habitat in the intervening impoundments (Isom 1971) and the limited dispersal capabilities of freshwater snails (Brown et al. 2008). Greenwood and Thorp (2001) suggested that Lithasia spp. are vulnerable because of their affinity to specialized habitats (e.g., clean rocky substrates in larger streams) and their inability to disperse due to impoundments. Almost the entire area separating the Ohio River population from those upstream in Tennessee and Cumberland rivers has changed from lotic to lentic habitat through the creation of two large impoundments (Lake Barkley and Kentucky Lake). In addition, two locks and dams are present on the Ohio River between the population we discovered in Illinois and those in the nearby lower Tennessee and Cumberland rivers. It seems probable that the impounding of the lower Tennessee and Cumberland rivers eliminated historical intervening populations of L. geniculata in those rivers. Isom (1971) stated that the decline of pleurocerids throughout the Tennessee River Valley was associated with habitat alteration as a result of impoundments, but offered no substantiating data. Neves et al. (1997) stated that impoundments have had a detrimental effect on freshwater gastropods “although poorly documented.” We have found no studies specifically documenting the effects of impoundments on gastropods. While speculation that impoundments have negative effects on riverine gastropods seems intuitive, data supporting such claims await further studies. It is beyond the scope of our study to determine if the Ohio River population is native or introduced; however, based upon the FMNH and OSUM specimens, records from Gooch et al. (1979) in Kentucky Lake (river mile 145) and Pickwick Reservoir (river mile 257) and the fact that snails are an understudied group (Lysne et al. 2008), it seems likely that the populations upstream of Kentucky Lake and Lake Barkley were contiguous with the Ohio River population before the Tennessee and Cumberland rivers were impounded. We suspect that the native range of L. geniculata included the lower Ohio River from upstream as far as Louisville, KY, to the confl uence with the Mississippi River at Cairo, IL, and that the Ohio River populations went undetected until our survey. Additional fieldwork is necessary to further elucidate the range of L. geniculata in the Ohio River. Lysne et al. (2008) listed four conservation challenges that freshwater gastropods face, including negative effects from invasive species. The L. geniculata collected contained numerous (7–33) Dreissena polymorpha (Pallas) (Zebra Mussel) attached, as did other live snails present, including Lithasia armigera (Say) (Armored Rocksnail), Lithasia verrucosa (Rafinesque) (Verrucose Rocksnail), and Pleurocera canaliculata (Say) (Silty Hornsnail). In addition, we saw hundreds of dead snails (all species listed above) infested with Zebra Mussels. We can only speculate that the Zebra Mussels caused the snails’ demise. Zebra Mussels have been known to colonize pleurocerids and pose a threat to their survival (Greenwood and Thorp 2001, Tucker 1994). Greenwood and Thorp (2001) suggested that Zebra Mussels might negatively affect gastropods by biofouling (e.g., impeding feeding, growth, movement, respiration, and reproduction), as has been reported for freshwater mussels (Hebert et al. 1991, Strayer and Malcom 2007). Greenwood and Thorp (2001) also suggested that Zebra Mussel infestations increase with water depth, and reported that very 2010 Southeastern Naturalist Notes 175 few Lithasia they found were encrusted with Zebra Mussels. However, we noticed that all Lithasia spp. we encountered were fouled with Zebra Mussels in the shallows of the river. Some individuals resembled “golf balls” as reported by Greenwood and Thorp (2001) for P. canaliculata from the deeper portions of the Ohio River. Another conservation challenge for aquatic gastropods is loss of habitat pertaining to water demand (Lysne et al. 2008). We observed several thousand pleurocerids (all species listed above) and other mollusks (both bivalves and gastropods) marooned at the Mound City site due to the drastic drop in water levels. The Ohio River is a highly regulated stream with over 20 locks and dams from the origin at Pittsburgh, PA, to the confl uence with the Mississippi River at Cairo, IL. The fl uctuation in water levels to regulate the navigation channel can leave shoals exposed, causing mollusks to be stranded and at risk of desiccation. As seen with freshwater mussels (Golladay et al. 2004, Metcalf 1983), it is assumed that drought-like conditions can cause movement restrictions, physiological stress, and even death for aquatic gastropods. Given the global conservation status of G3 (vulnerable to extirpation or extinction) assigned to L. geniculata by Minton and Lydeard (2003) and the distance to the populations upstream of Kentucky Lake and Lake Barkley, efforts (e.g., listing at the state level) should be taken to protect the Ohio River population. Future studies could include additional sampling methods (e.g., trawling and diving) to assess the full range and habitat preference of the species, and genetic analysis to determine if the Ohio River population is unique. Acknowledgments. Funds were provided in part by a grant from the Illinois Department of Natural Resources’ Wildlife Preservation Fund and the Illinois Department of Transportation. C. Phillips assisted in collecting. D. Foighil (UMMZ), J. Gerber (FMNH), T. Pearce (CM), D. Roberts (CA), J. Slapcinsky (UF), and T. Watters (OSUM) generously provided access to specimens and data under their care. H. Dunn and L. 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Williams. 1998. Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society, Special Publication 26. 526 pp. 1Illinois Natural History Survey, Institute of Natural Resource Sustainability at University of Illinois Urbana - Champaign, 1816 South Oak Street, Champaign, IL 61820. *Corresponding author - jtiemann@illinois.edu.