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
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,
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. Koch shared their specimens from the lower Cumberland River. S.
Chance, G. Levin, R. Minton, J. Sickel, and B. Tiemann offered comments and constructive
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1Illinois Natural History Survey, Institute of Natural Resource Sustainability at University of
Illinois Urbana - Champaign, 1816 South Oak Street, Champaign, IL 61820. *Corresponding
author - email@example.com.