Distribution and Conservation Status of the Freshwater Gastropods of Nebraska Bruce J

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Transactions of the Nebraska Academy of Sciences Nebraska Academy of Sciences and Affiliated Societies 3-24-2017 Distribution and Conservation Status of the freshwater gastropods of Nebraska Bruce J. Stephen University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/tnas Part of the Biodiversity Commons, and the Marine Biology Commons Stephen, Bruce J., "Distribution and Conservation Status of the freshwater gastropods of Nebraska" (2017). Transactions of the Nebraska Academy of Sciences and Affiliated Societies. 510. http://digitalcommons.unl.edu/tnas/510 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 Societies by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Distribution and Conservation Status of the freshwater gastropods of Nebraska Bruce J. Stephen School of Natural Resources, University of Nebraska, Lincoln, 68583, USA Current Address: Arts and Sciences, Southeast Community College, Lincoln, 68520, USA. Correspondence to: [email protected] Abstract: This survey of freshwater gastropods within Nebraska includes 159 sample sites and encompasses the four primary level III ecoregions of the State. I identified sixteen species in five families. Six of the seven species with the highest incidence, Physa gyrina, Planorbella trivolvis, Stagnicola elodes, Gyraulus parvus, Stagnicola caperata, and Galba humilis were collected in each of Nebraska’s four major level III ecoregions. The exception, Physa acuta, was not collected in the Western High Plains ecoregion. Seven indigenous species, Valvata tricarinata, Helisoma anceps, Campeloma decisum, Galba bulimoides, Physa jennessi, Ferrissia rivularis, and Planorbula armigera, display incidence rarity, being collected at five or fewer samples sites. The non-indigenous Chinese mystery snail, Bella- mya chinensis, was collected at five sites all within southeastern Nebraska. The Nebraska Sand Hills had the highest species richness, with 12 species. The wetland complex with the highest species richness of 8 was the lakes region of the Nebraska Sand Hills. Reservoirs and permanent/semi-permanent water bodies were the most species rich among water body types and hydrologic con- ditions with 13 and 14 species respectively. I assign a tentative conservation status to each species of indigenous freshwater snail observed following a modified quartile analysis. Keywords: Freshwater snails, malacology, macroinvertebrates, conservation, biogeography. doi: 10.13014/K2C24TCJ Introduction lists agricultural pollution as the leading impact source Aquatic invertebrate fauna, including freshwater on rivers and lakes (EPA 2002) and aquatic habitats have snails, have high extinction rates. The modeling of ex- been lost completely in Nebraska because of conversion to tinction rates of freshwater fauna suggests that they are agriculture (USGS 1996). Currently in Nebraska a single five times those of terrestrial animals (Ricciardi and Ras- freshwater gastropod species, Fossaria techella, is listed as mussen 1999). The non-marine mollusks collectively are a conservation concern (Schneider et al. 2011). Because no thought be one of the most threatened groups of organ- comprehensive study of freshwater snails has ever been isms (Lydeard et al. 2004) with freshwater snails, spe- conducted in Nebraska this lack of listings of freshwa- cifically, heading the list of endangered groups in sev- ter snail species is due to the absence of data not the ab- eral analyses (Allan and Castillo 2007, Lysne et al. 2008). sence of species in need. Recent surveys of Nebraska’s Thirty-nine percent of North American snail species have mollusks include freshwater snails and mussels in the a conservation ranking of G1, critically imperiled, with a Platte and Niobrara rivers (Freeman and Perkins 1992, further twelve percent at G2, imperiled (Lysne et al. 2008), 1997) and a statewide survey of mussels (Hoke 2011). An and many species of freshwater snail in North America analysis of the conservation status of freshwater snails for are thought to already be extinct (Master et al. 2000). Eval- North America has been completed recently (Johnson et uation of IUCN Red List shows that extinction of mol- al. 2013). This assessment lacks current survey data, which lusks in general may be double what has previously been is sparse in most areas of the continent, relying heavily thought, with the greatest number of extinctions from the of historic records and lacks detailed analysis within spe- USA (Régnier et al. 2009). These losses may already have cific regions and states. greatly altered systems because loss of species alters eco- Evaluation of the conservation status of species is system services by altering flow-through of energy and based on their abundance or rarity (Master et al. 2009). the resilience of the system (Contanza et al. 1997). The Abundances patterns of species often assume a com- three leading threats to freshwater fauna are alteration of petitive aspect based on resources within a community sediment and nutrient load from agriculture, altered wa- being divided among species (MacArthur 1957). One ter flow, and non-indigenous species invasions (Richter possible pattern is explained by the sequential niche frag- et al. 1997). The 2000 National Water Quality Inventory mentation model (Tokeshi 1990, 1992). Sequential niche 32 2017 Transactions of the Nebraska Academy of Sciences 37, 32–39 Bruce J. Stephen fragmentation fits the relative abundance of species and Analysis of species incidence data via the quartile the overall pattern suggests a minimal structure of bio- method, suggested by Gaston (1994), as modified by the logical communities that can be found in freshwater snail FWGNA project (Dillon 2012) allowed division of species communities (Gaston 1994, Dillon 2000). I utilize this pat- into regional conservation ranks as developed by the Na- tern in evaluating the conservation status based on spe- ture Conservancy and NatureServe (Master et al. 2009): cies incidence following Dillon (2012). Incidence based Following this, the 5% of species with the lowest inci- status may be adjusted once other aspects of species rar- dence are designated S1, critically imperiled regionally. ity including geographic distribution and habitat speci- The 20% left in the first quartile are S2,imperiled region- ficity are taken into account (Rabinowitz 1981). ally. The second quartile are S3, uncommon in region, the Though many species appear in danger of extinction, in- third S4, apparently secure, and the fourth quartile are S5, formation on presence, habitat use, and geographic distri- demonstrably secure. Some adjusting of species quartiles bution is absent for many freshwater snails within North was done to keep species with the same incidence value America (Brown et al. 2008, Lysne et al. 2008). The need for within the same conservation status. This resulted in dif- surveys and distributional trends of freshwater gastropods ferent number of species in each quartile. is urgent (Lydeard et al. 2004, Lysne et al. 2008). A survey Species identification proceeded first by separating of Nebraska freshwater gastropods is essential to provid- snails by gross morphological characteristics. I exam- ing data on population decline or demise, which may in ined at least three specimens, when available, from each turn inform other issues including habitat suitability, wa- morphologic type using a hand lens or microscope to de- ter quality, and influences of snail populations on other termine species via fine morphological characters. Un- species. By utilizing recent survey data of others and sur- less a distinct morphological difference was apparent I veying across the State I assess species distribution and the assumed all specimens from a gross morphologic group conservation status of Nebraska’s freshwater snails. were the same species. Species identification is challeng- ing for some freshwater snails, contrasting characteristics Materials and Methods and a glut of taxonomic names are used (Burch 1989). I I surveyed freshwater snails from 91 sample sites use the taxonomy advocated by Johnson et al. (2013): Ap- throughout Nebraska between 2007 and 2014. In addi- pendix A includes my assessment of generic and specific tion, 68 samples, collected primarily by Steve Schain- synonyms. Species of Physidae, in particular, are prob- ost between 2001 and 2010, were obtained from the Ne- lematic to identify (Wu 2004-2005, Dillon et al. 2013). I braska Game and Parks Commission. I targeted areas of identified Physidae species asPhysa acuta when a distinct high wetland density or wetland complexes such as sec- shoulder was present and as Physa gyrina when whorls tions of the Nebraska Sand Hills and the Rainwater Ba- partially overlapped. Externally Physa acuta and Physa po- sin Plain but attempted to cover the entire State sampling milia are morphologically similar and I did not determine within each of four level III ecoregions, the Western High any distinct difference that enabled me to identify any Plains (WHP), the Central Great Plains (CGP), the Ne- snail as Physa pomilia. A few specimens were sub-fossils braska Sand Hills (NSH), and the Western Cornbelt Plains or were very small

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