INTRODUCTION

With less than 25% of the fauna considered stable (Williams et al., 1993), native freshwater mussels (Mollusca: Bivalvia: Unionidae and Margaritiferidae) are one of the most endangered groups of animals in North America (Stein et al. 2000). In Missouri, 10 species are listed as state endangered, 9 of which are also either federally endangered or candidate species; 19 other species are considered Missouri Species of Conservation Concern (SOCC). With 42% of the statewide fauna considered to be SOCC, freshwater mussels rank second only to crayfish in terms of imperilment in Missouri (MDC 2011). Documenting the distribution and diversity of freshwater mussels is a key aspect of their conservation (NNMCC 1998, MDC 2008).

Previous survey efforts in the Lamine River basin have documented 30 species, including 2 SOCC: Anodonta suborbiculata Say, 1831, and Ligumia recta (Lamarck, 1819) (Utterback, 1915–1916, 1917; Oesch, 1995) (Table 1). Utterback (1915–1916, 1917) documented 21 species from the Blackwater River portion of the basin, but unfortunately included few specific details about collection locations or species distributions. Oesch (1995) reported 30 species from 10 locations in the basin, adding 9 species to the fauna that had not been previously reported: Fusconaia flava (Rafinesque, 1820), Obliquaria reflexa Rafinesque, 1820, Pleurobema sintoxia (Rafinesque, 1820), Potamilus alatus (Say, 1817), Potamilus ohiensis (Rafinesque, 1820), Quadrula pustulosa (Lea, 1831), Truncilla donaciformis (Lea, 1828), Truncilla truncata Rafinesque, 1820, and Venustaconcha ellipsiformis (Conrad, 1836). Other than these limited survey efforts, little was known of the diversity and distribution of freshwater mussels in the Lamine River basin. This survey was conducted to document the distribution, diversity and abundance of unionid mollusks, in particular SOCC, in the Lamine River Basin.

The Lamine River is the 3rd largest free-flowing river in Missouri (Brown et al., 1992), and together with its largest tributary (Blackwater River), the basin drains approximately 6863 km² of the Central Plains Aquatic Subregion (Sowa et al., 2005) in west central Missouri (Figures 1 and 2). This subregion was largely glaciated during the Pleistocene Epoch, and is characterized by low, rolling plains. Surface runoff is the primary source of water to typical streams within the subregion, and stream discharge fluctuates widely from extremely low base flow conditions to relatively high peak discharges following rain events (Sowa et al., 2005, 2007). The Lamine River is an Ozark border stream (Pflieger, 1989), and is unique because it straddles the border between the largely glaciated Central Dissected Till Plains and unglaciated sections of the Ozarks (Sowa et al., 2005). Tributary streams from the west tend to be of a lower gradient and primarily turbid, with sand and silt substrates, while tributaries from the south and east tend to be clear with gravel substrates similar to Ozark streams (Sowa et al., 2005).

Historically the basin was dominated by tallgrass prairie to the west, transitioning to oak and mixed-hardwood forested areas in the east (Sowa et al., 2005). Presently, landuse in the basin is largely agricultural, either row crops or pasture, with only a few remnants of native prairie remaining (MDNR, 2008). There are a number of sizeable communities in the basin, each of which has numerous permitted point source discharges. Threats and impacts to the basin's mussel fauna include point source pollution discharges, channelization, head cutting, nonpoint source runoff, gravel mining operations, and invasive species (Brown et al., 1992). Brown et al. (1992) considered aquatic habitat quality to be fair throughout the Lamine River portion of the basin, however lack of riparian corridor and areas of intensive streambank erosion were prevalent in select areas. Fortunately, approximately 92% of the mainstem Lamine River remains unmodified (Brown et al., 1992). In contrast, many streams in the Blackwater River portion of the basin, including the Blackwater River mainstem itself, have been extensively channelized (S.E. McMurray, pers. obs.).

METHODS

Freshwater mussels were qualitatively sampled by experienced personnel with timed searches at 45 locations from 2003 to 2006 (total search time = 86.1 person hr, average time/site = 1.9 person hr) (Fig. 1 and 2, Appendix A). Timed, qualitative searches were conducted to maximize species richness and optimize our ability to detect rare species (Strayer et al., 1997; Vaughn et al., 1997). Search time at each location was dependent upon stream size and the amount of area that could be searched. Sampling locations were chosen in the field based on availability and quality of habitat (e.g., stable substrates, suitable flow) and signs of mussel assemblages (e.g., shell material on gravel bars, live animals observed), and were accessed via public or private accesses, bridge crossings, or boat. These sites included new as well as previously surveyed locations. Additional collections of shell material, previously unreported, were made between 1995 and 1999 by Missouri Department of Conservation (MDC) staff.

Depending upon water clarity and depth mussels were surveyed visually with snorkeling or view scopes or with tactile searches, in all available habitats. All mussels were identified, counted, and returned to the substrate; shell material was also collected from each location. Length measurements (anterior to posterior margins) were made from all mussels collected from 4 assemblages in the Lamine River (locations 4, 10, 22, 27), 1 assemblage in Muddy Creek (location 28), and 1 assemblage in Spring Fork (location 37) (Figures 1 and 2). Nomenclature largely follows Turgeon et al. (1998), except where accepted taxonomic changes have occurred. Conservation status follows Williams et al. (1993) and the Global Rank and State Rank of each species observed follow MDC (2011) and NatureServe (2010). The Global Rank is an assessment of global imperilment primarily based on the number of occurrences worldwide, and range from G1 (Critically Imperiled) to G5 (Secure) (MDC, 2011; NatureServe, 2010). The State Rank is a measure of imperilment primarily based on the number of occurrences of a species in Missouri, and as with Global Ranks ranges from S1 (Critically Imperiled) to S5 (Secure) (MDC 2011).

RESULTS

We observed 5287 individuals representing 27 species at the 45 locations surveyed in the basin (Appendix A). Average Catch per Unit Effort (CPUE, live individuals/person hr) for all survey locations was 54.7, ranging from 0 to 417.6. Amblema plicata was by far the most dominant species collected with 2989 individuals occurring at 34 of 45 sites (75.5%), representing 56.5% of live mussels collected (Table 2). Leptodea fragilis and Potamilus alatus were the most commonly encountered species, each occurring at 36 locations. Including A. plicata, 12 species had relative abundance values greater than 1.0%. A majority of the species observed (n=15) had relative abundance values less than or equal to 1.0% (Table 2). The invasive species Corbicula fluminea (Müller, 1774) was observed live at nearly all sampling locations throughout the basin, but counts of individuals were not made.

At the 6 locations where length measurements were collected the most dominant species observed, Amblema plicata, ranged from 25 – 156 mm in shell length (n = 146, = 108.4 ± 32.3 mm). With the exception of Lampsilis cardium (n = 28, 57 – 159 mm, = 126. 4 ± 30.0), Obliquaria reflexa (n = 37, 27 – 82 mm, = 64.4 ± 12.2), and Quadrula quadrula (n = 70, 29 – 127 mm, = 97.329 ± 23.9) the most abundant species observed were largely represented by larger, and therefore older, individuals (Figure 3).

FIGURE 1

Qualitative freshwater mussel survey sites in the Lamine River, Missouri, 2003 – 2006. Inset shows the location of the basin in Missouri.

Nearly all of the 27 species observed during this survey effort were found in the Lamine River mainstem, with 3 species (Ligumia recta, Ellipsaria lineolata and Venustaconcha ellipsiformis) restricted to the mainstem of that river. Megalonaias nervosa (Rafinesque, 1820) was only found live in the Lamine River mainstem, but was represented by shell material from a single location in Muddy Creek, a Lamine River tributary. Ligumia subrostrata (Say, 1831), Pyganodon grandis (Say, 1829), and Toxolasma parvum (Barnes, 1823) were only represented by shell material in the mainstem Lamine River, but were found live in other portions of the basin. Uniomerus tetralasmus (Say, 1831) was the only species that did not occur in the Lamine River mainstem; it was restricted to the South Fork Blackwater River and Flat Creek.

Most of the species observed in the present survey were S4 or S5 species (Apparently Secure or Secure, respectively) (MDC 2011). A single Missouri SOCC, Ligumia recta, was represented by a total of 4 live individuals at 4 locations in the Lamine River mainstem. Weathered and subfossil shell material was collected at an additional 9 locations also in the Lamine River mainstem. Globally, L. recta is a G5 (Secure) species, but is an S2 (Imperiled) species in Missouri (MDC 2011, NatureServe 2010.

FIGURE 2

Qualitative freshwater mussel survey sites in the Blackwater River, Missouri, 2003 – 2006. Inset shows the location of the basin in Missouri.

DISCUSSION

With a fauna of 30 species, freshwater mussel diversity in the Lamine River basin is similar to Ozark streams in the Missouri River system, such as the Sac River (39 species; Hutson & Barnhart, 2004; MDC, unpubl.), Pomme de Terre River (31 species, Hutson & Barnhart, 2004), and Gasconade River (43 species; Buchanan, 1994; Bruenderman et al., 2001; MDC, unpubl. data). In contrast, the Lamine River basin is much more diverse than prairie rivers in the Missouri River system such as the Platte River (12 species, MDC, unpubl. data) and Grand River (19 species, MDC, unpubl. data). This is reflective of the ichthyofauna of these systems, with Ozark rivers being more diverse than their prairie counterparts (Pflieger, 1997).

The dominant species in the Lamine River basin, Amblema plicata, is relatively common and widely distributed in the Midwest (Cummings & Mayer, 1992) and in Missouri (Oesch, 1995). Amblema plicata is a habitat generalist, appears to be tolerant of a wide range of water quality, and therefore may become a dominant species in many river systems (Oesch, 1995). Amblema plicata has been found to be the dominant species in other river systems with varying degrees of impacts similar to those observed in the Lamine River basin (i.e., high sediment loads, hydromodification). Ahlstedt & Jenkinson (1991) reported that A. plicata represented >54% of the mussels collected in the lower St. Francis River (Missouri and Arkansas). Hutson & Barnhart (2004) reported that A. plicata represented 43% of the mussels collected in the Pomme de Terre River (Missouri). Wentz et al. (2009) reported that A. plicata represented >55% of the mussels collected in the Tyronza River (Arkansas).

While qualitative visual or tactile searches without excavation tend to oversample large or sculptured species and underestimate smaller species and individuals (Obermeyer, 1998), Christian et al. (2005) concluded that visual and tactile searches by experienced personnel could reveal recruitment when it was occurring. Few small juveniles (< 20 mm total shell length) were observed in the samples that were measured, and our size frequency distributions indicated unimodal recruitment patterns in the 9 most abundant species in the basin. This paucity of juveniles could be due to a lack of recent recruitment. However, given the intrinsic variability in freshwater mussel recruitment, even sporadic patterns of recruitment can sufficiently maintain populations (Neves & Widlak, 1987; Payne et al., 1997).

FIGURE 3

Size frequencies of 9 of the most abundant species collected from 6 locations in the Lamine River basin, Missouri, 2003 – 2006.

Three species previously reported to occur in the basin were not observed in the present survey. Utterback (1915–1916, 1917) reported Cyclonaias tuberculata (Rafinesque, 1820) and Lasmigona costata (Rafinesque, 1820) as “fairly abundant” and Anodonta suborbiculata as “scarce”. Based on Utterback (1915–1916, 1917) Oesch (1995) also reported each of these species from the Blackwater River portion of the basin prior to 1920, but no more recent collections were noted. These species have apparently been extirpated from the basin, presumably due to the extensive modification of the Blackwater River.

Corbicula fluminea was common and abundant throughout the basin, and it has been demonstrated that increased ammonia levels following large-scale die-offs of C. fluminea are detrimental to native mussels (Cooper et al., 2005). No Dreissena polymorpha Pallas, 1769, were observed in the Lamine River basin. However, D. polymorpha occurs in the Missouri River basin and several reservoirs in Missouri (MDC, unpubl. data). Private watercraft can move freely between the Lamine and Missouri rivers, and other infested waterbodies, and therefore could aid in the dispersal of this invasive species into the Lamine River system.

Notwithstanding the anthropogenic impacts occurring in the basin, the Lamine River basin has a diverse freshwater mussel fauna, and a number of species rich mussel assemblages were observed in the mainstem Lamine River. Continuing with management objectives proposed by Brown et al. (1992) to maintain water quality, improve aquatic habitat, and work with private landowners to stabilize streambanks and improve riparian zones will be necessary to maintain the diversity of freshwater mussels in the Lamine River basin.

TABLE 1

Freshwater mussel (Bivalvia: Unionidae) species reported from the Lamine River basin, Missouri, from Utterback (1915–1916, 1917, “Blackwater River Basin”), Oesch (1995), and present survey.

(cont.)

TABLE 2

Number collected, number of occurrences (live and dead) and percentage of sites, and relative abundance of freshwater mussels collected in the Lamine River basin, Missouri presented in order from highest to lowest relative abundance.

(cont.)