An assessment of the relation between metal contaminated sediment and freshwater mussel populations in the Big River, Missouri.

The Big River in southeast Missouri drains the largest historical lead mining area in the United States. Ongoing releases of metal contaminated sediments into this river are well documented and are suspected of suppressing freshwater mussel populations. We characterized the spatial extent of metal contaminated sediments and evaluated its relationship with mussel populations in the Big River. Mussels and sediments were collected at 34 sites with potential metal effects and 3 reference sites. Analysis of sediment samples showed that lead (Pb) and zinc (Zn) concentrations were 1.5 to 65 times greater than background concentrations in the reach extending 168 km downstream from Pb mining releases. Mussel abundance decreased acutely downstream from these releases where sediment Pb concentrations were highest and increased gradually as Pb sediment concentrations attenuated downstream. We compared current species richness with historical survey data from three reference rivers with similar physical habitat characteristics and human effects, but without Pb-contaminated sediment. Big River species richness was on average about one-half that expected based on reference stream populations and was 70-75 % lower in reaches with high median Pb concentrations. Sediment Zn and cadmium, and particularly Pb, had significant negative correlations with species richness and abundance. The association of sediment Pb concentrations with mussel community metrics in otherwise high-quality habitat indicates that Pb toxicity is likely responsible for depressed mussel populations observed within the Big River. We used concentration-response regressions of mussel density verses sediment Pb to determine that the Big River mussel community is adversely affected when sediment Pb concentrations are above 166 ppm, the concentration associated with 50 % decreases in mussel density. Based on this assessment of metals concentrations sediment and mussel fauna, our findings indicate that sediment in approximately 140 km of the Big River with suitable habitat has a toxic effect to mussels.

New microsatellite markers for Ellipse, Venustaconcha ellipsiformis (Bivalvia: Unionidae), with notes on optimal sample size and cross-species amplification.

Venustaconcha ellipsiformis (Unionidae) is a freshwater mussel species inhabiting small to medium streams of the Midwestern United States; however, its occurrence is rather sporadic and populations are often isolated. Due to anthropogenic habitat degradation and water pollution, this species is designated as some sort of conservation status in many states. To prioritize conservation strategies, highly variable genetic markers are necessary to assess population genetic structure and potential genetic erosion of V. ellipsiformis. Using whole genome sequence data, we developed and characterized microsatellite markers for V. ellipsiformis. Among 23 tetranucleotide loci tested, 14 loci were consistently amplified and showed polymorphism. Analyses performed on three populations in the upper Mississippi River basin showed that the number of alleles per locus ranged from 2 to 11 and the observed heterozygosity varied from 0.15 to 0.75. Based on genotypic and allelic rarefaction curves, these loci had adequate statistical power to genetically discriminate between individuals and the sample size was large enough to capture most alleles available in the populations at most loci. Finally, cross-species screening of the loci successfully amplified and showed polymorphism in six species in the tribe Lampsilini. The microsatellite loci developed in this study provide a valuable addition to extant genetic markers for freshwater mussels and can be useful to provide high-level resolution of population genetic parameters for V. ellipsiformis. Such information will be of great value for resource managers developing and prioritizing conservation strategies for imperiled mussel species.