The Clinch and Powell rivers, Tennessee (TN) and Virginia (VA), upstream of Norris Reservoir, TN, are known for high freshwater mussel species diversity and endemism. Collectively, these rivers harbored at least 56 species historically and 49 are extant, many of which now survive only in the Clinch or Powell rivers or a few other streams. Among an unparalleled 24 federally endangered mussel species known from these rivers, 20 species are considered extant. We sampled 0.25 m^-2 quadrats at six Clinch River sites and four Powell River sites for a total of 4–6 sample years at each site. Overall trends were highly significant in the Clinch River, with mean mussel density at combined sites in each state increasing from 16.5 m^-2 to 41.7 m^-2 (p < 0.0001) at sites in TN but declining from 12.0 m^-2 to 3.3 m^-2 (p < 0.001) at sites in VA. Cumulative species richness was 39, ranging from 36 in TN to 27 in VA. Greater density in the Clinch River, TN, was due primarily to increases in Epioblasma capsaeformis, Medionidus conradicus, and Ptychobranchus subtentus, which were rare or undetected at most sites in 1979, but increased five- to ten-fold by 2004. Conversely, at Pendleton Island, VA, which was the best site for mussels in the river circa 1980, the decline in density was highly significant, from 24.6 m^-2 in 1979 to 4.6 m^-2 (p < 0.001) in 2004. In the Powell River, there was also a highly significant decline in mean mussel density at combined sites from 8.7 m^-2 to 3.3 m^-2 (p < 0.001), with a total of 33 species documented. Though species diversity remains relatively high, our results confirm that mussel populations have declined in large reaches of each river over the 25-year study period.

Freshwater mussels are a unique guild of benthic invertebrates that are of ecological and conservation importance. Age and growth determination are essential to better understand the ecological role of mussels, and to effectively manage mussel populations. In this study, we applied dendrochronology techniques and Ford-Walford analyses to determine growth parameters of mussel species collected in three Ouachita Mountain Rivers (Kiamichi, Mountain Fork, and Little Rivers). We collected six species of mussels, Actinonaias ligamentina, Amblema plicata, Fusconaia flava, Ptychobranchus occidentalis, Quadrula pustulosa and Quadrula verrucosa, created thin sections, and analyzed the internal annuli to determine growth and longevity estimates. Annual growth was validated in 12 of the 17 populations we sampled, and the series intercorrelation for the validated populations ranged from 0.108 to 0.477. The predicted average maximum validated age was 43 years, ranging from 15 to 79 years, while the growth constant (K) ranged from 0.038 to 0.137. Growth and longevity were inversely related. Growth patterns were more synchronous at local sites compared to river and regional scales, suggesting that local environmental conditions likely influence growth rates. This study provides the first reported growth parameters for mussels in Ouachita Mountain rivers of southeastern Oklahoma and will be useful in understanding the life history traits of these mussel populations.

Knowledge of the habitat suitability of freshwater mussels (family Unionidae) is necessary for effective decision making in conservation and management. We empirically measured microhabitat use for 10 unionid mussel species, including the U.S. federally endangered Alasmidonta heterodon, at 20 sites in the Tar River basin, North Carolina, USA. We also quantified habitat availability at each site, and calculated habitat suitability for each mussel species. The majority of available habitat across all sites consisted of shallow, slow-moving water with penetrable silt or sand substrate. Among species, mean water depth of occupied habitats ranged 0.23 – 0.54 m, mean bottom velocity ranged 0.001 – 0.055 m/s, average mean-column velocity ranged 0 – 0.055 m/s, and mean substrate penetrability ranged 0.11 – 11.67 on an index scale. The most commonly measured dominant substrate materials were silt, sand, very coarse sand, pea gravel, and coarse gravel. The most common cover types were coarse woody debris and fine woody debris. These findings revealed a relationship between the niche breadth and conservation status of four species. Federally endangered A. heterodon consistently showed a narrower suite of suitable microhabitats than the common mussel Elliptio complanata. The range of suitable habitat characteristics for Fusconaia masoni and Villosa constricta, listed as North Carolina (USA) state endangered and special concern, respectively, was typically narrower than those of E. complanata and wider than those of A. heterodon. These habitat suitability criteria and relationships will be useful to guide identification of suitable sites for habitat protection, mussel relocation, or site restoration.

Tulotoma magnifica is a federally threatened freshwater gastropod endemic to the Mobile Basin in Alabama. It was considered extirpated from the Alabama River until its rediscovery there in 2006. Tulotoma occurs primarily in colonies in large interstitial spaces beneath boulders and in bedrock crevices. We used side-scan sonar to identify boulder habitat in the Alabama River and to focus dive surveys at those sites. Eighty-five sites with potential Tulotoma habitat were identified with sonar and assessed by a diver. Colonies were found at five locations, three of which were previously unknown. Side-scan sonar greatly increased efficiency during this survey and was a useful tool.

Bithynia tentaculata is believed to have been extirpated from North America during the last glacial maximum. It was reintroduced into North America via the Great Lakes basin in the 1800's and has recently been expanding its geographic range. This snail serves as intermediate host for three trematodes that cause extensive recurring morbidity and mortality events in migratory water birds along the Mississippi River. Using twelve microsatellite loci for ∼200 individual snails from 11 populations in North America and Europe, we examined one of the three major geographic regions from which founding populations into the Great Lakes typically originate. Our data supports a single recolonization of North America into the Great Lakes Basin followed by subsequent introduction events from the Great Lakes to other large watersheds in North America. However, additional watersheds in Europe require sampling to confirm this result. No populations with genetic signatures indicative of North American glacial relics were found. The initial invasion of North America was likely not from the Ponto-Caspian basin, the usual source of freshwater invasive species to the Laurentian Great Lakes.

Invasive aquatic plants like hydrilla (Hydrilla verticillata) threaten native species in many ways, ultimately degrading overall habitat quality and quantity. Aquatic herbicides are often chosen as a control and management strategy, but few peer-reviewed studies address their effects on non-target organisms, especially native freshwater mussels and snails. The aim of this study was to assess the life stage sensitivity of a rare snail, Somatogyrus virginicus (Lithoglyphidae), to two aquatic herbicides (dipotassium salt of endothall and fluridone). We collected adult snails, cultured their eggs on a vinyl card substrate, exposed adults and eggs in 96-h static-renewal experiments, and monitored eggs through hatching. Because fluridone is typically applied for ≥ 60 d, an additional treatment was exposed in staticrenewal through hatching (30 d total) to improve environmental relevance. Eggs present on the shells of adult snails were also monitored. Endpoints were adult survival and egg hatching success. Fluridone did not affect adult snail survival at concentrations up to 1500 µg/L, and in the test with eggs on vinyl cards, fluridone did not significantly delay (p = 0.12) or influence overall hatching success (p = 0.22), including in the 30-d exposure (Dunnett's p = 0.09). However, fluridone significantly delayed hatching of eggs on adult shells (p < 0.01) and reduced their overall hatching success (p < 0.01). The 96-h median effect concentration (EC50) for fluridone on hatching success of eggs on adults was 1334 µg/L (95% CI, 1215 – 1466 µg/L). For endothall, the adult 96-h median lethal concentration (LC50) was 223 mg/L (157 – 318 mg/L). Endothall negatively affected hatching success in both egg tests by delaying hatching (p < 0.01 in both tests) and by reducing overall hatching success (p = 0.04 for eggs on cards, and p < 0.01 for eggs on adults). The endothall 96-h EC50s for egg hatching success were 54.1 mg/L (95% CI, 35.6 – 82.2 mg/L; eggs on adults) and 83.4 mg/L (95% CI, 60.4 – 115.2 mg/L; eggs on cards). Neither herbicide had toxic effects to either life stage at concentrations typically prescribed for control of hydrilla (5 – 15 µg/L fluridone and 1 – 5 mg/L endothall). However, applying the minimum amount of herbicide needed for effective weed control is recommended for ensuring safety of non-target organisms.

Freshwater mussels have undergone dramatic population declines due largely to habitat alteration. A commonly employed measure to minimize the effects of anthropogenic habitat disturbance on mussels is short-distance relocations of individuals. However, quantified survival data are lacking to gauge the success of relocations. To evaluate the suitability of short-distance relocations as a conservation tool for freshwater mussels, we experimentally relocated two common species, Mucket (Actinonaias ligamentina) and Plain Pocketbook (Lampsilis cardium), in an active construction zone. We marked 100 mussels with passive integrated transponders, released them ∼200 m upstream of the construction site, and monitored them monthly throughout the spring and summer 2013–2015. We used Cormack-Jolly-Seber models to estimate apparent survival rates and found survival was lowest the first two months after relocation but increased and stabilized thereafter. Our models predict 93% of the relocated A. ligamentina and 71% of the L. cardium remained alive three years post-relocation. We conclude short-distance relocations are a viable minimization tool for protecting freshwater mussels at bridge construction sites, but further study is needed examine the factors driving the initial mortality.