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Native freshwater mussel (Unionidae) mortality events have been occurring with increased frequency in recent decades, with few investigations into potential etiological agents. In the western United States, no surveys have been published regarding the bacteria associated with unionid mussels. Herein, we examine locations of known mussel mortality events in the Chehalis River (Washington), in the Crooked River (Oregon), and Owyhee River (Oregon). Mussel populations considered healthy were sampled in the Skookumchuck River (Washington) for comparison. A variety of bacteria were isolated from these populations, and most notably, Acinetobacter spp. were identified from 82% of moribund individuals of Gonidea angulata in the Owyhee River. Future work evaluating whether Acinetobacter spp. are pathogenic to freshwater mussels could be valuable in unraveling the factors associated with these enigmatic mortality events. [ABSTRACT FROM AUTHOR]

The presence of sub-micron-sized plastics in the environment has been increasing, with the possible risks of these particles remaining relatively unknown. In order to assess the toxicity of these particles, 100 nm diameter green fluorescent nano-polystyrene spheres (NPS) (20–60 mg/L) were exposed to zebra mussels (Dreissena polymorpha) to investigate the mortality, clearance rate and stress-related biomarker responses. D. polymorpha were collected and analysed with standard OECD toxicological tests and biomarker analysis to detect both physical and biochemical responses after exposure to NPS. The toxicity of the NPS to D. polymorpha was low, with 60 mg/L NPS causing a mortality rate of 11.1% at 96 h which was statistically significant compared to the 4.2% control. No statistical change could be found for the condition factor (kc) of D. polymorpha after NPS exposure. Clearance rates in D. polymorpha using R. subcapitata algae showed NPS-exposed mussels had a reduction of filtering efficiency of up to 30.5%. Bioassay testing shows a mixed but undeniably negative response from the D. polymorpha to the NPS, notably a significant rise in DNA Strand Breaks (DSB) and Metallothionein (MT) responses for high NPS concentrations. Additionally, Lipid Peroxidation (LPO) and Ferric Reducing Antioxidant Power (FRAP) assay tests showed a significant increase in response from the higher (>40 mg/L) concentrations of NPS exposure. Although Glutathione S-Transferase (GST) assay showed no statistical change from the control for all NPS-exposed samples, an increase of 20% had occurred for 60 mg/L NPS. Overall, a minimal toxic response from D. polymorpha to the NPS exposure below 40 mg/L was seen. After 40 mg/L NPS, mussels presented more acute toxicity in terms of mortality, along with reduced algal clearance rates and anincrease in biomarker response. This study revealed a clear induction of oxidative stress and DSB in the digestive gland of zebra mussels following exposure to nano-polystyrene. While these findings provide valuable insights into the potential harmful effects of nanoplastics in freshwater bivalves, further studies are necessary to help understand the level of threat plastic pollution may pose to the health of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Freshwater mussels are a globally threatened taxon, but little is known about population trajectories for species outside Europe and North America. To contribute to understanding of mussel conservation status outside these regions, we surveyed mussel and other invertebrate populations in waterbodies across Dhaka, Bangladesh, to assess population trends and the role of mussels in structuring benthic communities.We found that mussel populations in Dhanmondi Lake, our focal waterbody, have declined in density by approximately 90% between 2010 and 2023. Lamellidens marginalis declined by 90.8% from an average density of 47.9 ± SE 7.1 mussels 0.25 m−2 in 2010 to 4.4 ± SE 0.7 mussels 0.25 m−2 in 2023, while Indonaia caerulea declined by 89.4% from an average density of 6.6 ± SE 1.0 mussels 0.25 m−2 in 2010 to 0.7 ± SE 0.1 mussels 0.25 m−2 in 2023.Previously detected associations between mussels and other invertebrate taxa, and between mussels and community composition, have been lost. Non‐mussel invertebrates have also declined significantly, with an average decrease in abundance of 27%, alongside decreases in family richness and Shannon‐Wiener diversity. These declines occurred despite apparent improvements in water quality.Findings from other waterbodies across Dhaka also suggest the loss of mussel species including L. marginalis, I. caerulea and Parreysia corrugata from some locations, as well as the presence of the non‐native mussel Pilsbryoconcha exilis at river sites.Our results reflect a wider, global pattern of enigmatic declines in freshwater mussels and the possible loss of associated ecosystem functioning, which may be going unnoticed in less‐studied areas including the subtropics. [ABSTRACT FROM AUTHOR]

The presence of predators influences the selection of oviposition sites, with females often choosing locations that minimize the risk of predation. Bitterlings, freshwater fish that deposit their eggs into the gills of mussels, face the threat of predation from mussel-associated leeches Hemiclepsis kasmiana, which feed on bitterling embryos. In this study, we investigated the host preferences of two species of spring-spawning bitterlings, Tanakia limbata and T. lanceolata, based on the parasitic density of mussel-associated leeches. Our methodology involved observing female bitterling spawning behavior and dissecting mussels to locate bitterling embryos. Our results revealed a preference of female T. limbata for spawning on uninfested mussels or those with lower leech infestation densities, supported by both spawning observations and mussel dissections. Female T. lanceolata exhibited a tendency to avoid mussels with higher leech infestation densities, supported by only mussel dissections, although this avoidance is not statistically significant. The difference in host preference between the two spring-spawning bitterling species may be due to their contrasting reproductive strategies aimed at minimizing the total risk of predation and host mortality. [ABSTRACT FROM AUTHOR]

Understanding the age structure and growth patterns of freshwater bivalve species is crucial for their conservation, and these data are still lacking for many species and locations. The main objective of this study was to gain insight into the age structure and growth patterns of the endangered mussel Unio crassus at the unpolluted and polluted sites on the Mrežnica River (Croatia), as well as construct the first-ever chronology for this species. Bivalve sampling was carried out in July 2020. The age and growth dynamics were determined by analysing internal growth lines in acetate peel replicas of shell cross sections. The length range of shells from the unpolluted station was 4.5–5.6 cm, with an estimated age range of 10 to 29 years, whereas shell length at the polluted site was 5.2–6.1 cm, with an estimated age range of 10 to 22 years. Our results indicate that industrial pollution may influence life strategies in U. crassus populations, with mussels growing faster and living shorter at polluted site. Compared to other parts of Europe, the estimated ages obtained in our study were the most similar to those in central Europe. According to growth curves, mussels grow the fastest during their first 10 years, after which their growth significantly slows down. Growth chronologies were constructed by measuring growth increments in acetate peels of shell cross-section, and some correlations between shell growth and environmental parameters have been observed, indicating the potential for further sclerochronology research on this species. [ABSTRACT FROM AUTHOR]

Global increase in aquaculture production has created a need to reduce its environmental impacts. Nutrients could be recycled especially at land-based recirculating aquaculture systems (RAS) by cultivating green microalgae in aquaculture effluent. However, microalgae are difficult to harvest. As a multi-trophic solution, mussels could be used in harvesting microalgae. We tested three European freshwater mussels (duck mussel Anodonta anatina, swan mussel A. cygnea, and swollen river mussel Unio tumidus) for filtering two common green microalgae (Monoraphidium griffithii and Selenastrum sp.) grown in RAS effluent. Mussels decreased microalgal concentrations in the tanks 42–83% over three consecutive trials. Algal concentrations at the end of each trial were lowest for both microalgae in tanks containing Anodonta mussels. Clearance rates were higher for Anodonta mussels than for U. tumidus. Mussels biodeposited more microalgae to tank bottoms when M. griffithii was filtered. Ammonium concentration decreased or did not change in tanks with M. griffithii, but increased in tanks containing Selenastrum sp. These results suggest that of the tested species Anodonta mussels and M. griffithii show best potential for RAS effluent bioremediation application. We conclude that a co-culture of microalgae and unionid mussels could be used for recycling nutrients in aquaculture. [ABSTRACT FROM AUTHOR]

Ecosystem engineers alter habitat and resource availability within ecosystems, but the magnitude of these effects depends on abiotic context and spatial scale. We examined how the effects of freshwater mussels, an ecosystem engineer, changed with spatial scale. We combined a field enclosure experiment and comparative field study to evaluate associations among mussels and macroinvertebrate communities across three spatial scales: mussel individuals (~ 0.01 m2), patches of mussels (0.25 m2), and large aggregations of many mussel patches (mussel beds, ~ 1000 m2). We used canonical correspondence analysis and variation partitioning to evaluate how mussel abundance, food availability, substrate heterogeneity, and flow influenced macroinvertebrate communities. We found that mussels' influence on macroinvertebrate communities differed among spatial scales. At the smallest scale, macroinvertebrate density increased on the shells of live mussels, likely due to mussel influences on food availability to grazers. At the patch scale, we found no mussel effects, likely because they were overridden by a flood event. At the mussel bed scale, macroinvertebrate communities were primarily controlled by flow and secondarily by food availability. As such, the continued loss of freshwater mussels means the loss of habitat creation and food provisioning for other aquatic groups, and alteration of facilitation landscapes within streams. [ABSTRACT FROM AUTHOR]

Unionid mussels deposit growth rings (annuli) within the shell, which can be used to estimate age and growth. Thin-sectioning is a common technique for counting annuli, wherein a cross-section of a shell valve is taken and evaluated by multiple readers. Correctly identifying annuli can be challenging because ambiguous annuli can bias growth estimates. Staining with calcein, a fluorescent chemical, is a technique that has been used with marine and freshwater species to improve accuracy of growth estimates. This method chelates calcium, causing a permanent mark that fluoresces under ultraviolet light. Calcein has seen limited testing on unionid mussels so it remains unclear if this method has adverse effects on survival and growth. We evaluated calcein against 2 concentrations (125 mg L−1 and 250 mg L−1) at 2 exposure times (12 and 24 h) on Cyclonaias pustulosa, a common North American unionid. Survivorship remained above 80% 6 months post-immersion. Mark quality and retention for 250 mg L−1 were high for both 12- and 24-h immersions, although historical annuli were not highlighted. These findings corroborate studies indicating calcein immersion is generally safe and effective in juveniles and adults and suggest it may be useful in validating new growth. [ABSTRACT FROM AUTHOR]

Qualitative and quantitative sampling efforts in the Verdigris River, OK (upstream of Lake Oologah), yielded new distributional records of 2 freshwater mussel species of conservation need: Cyprogenia aberti (Western Fanshell) and Ptychobranchus occidentalis (Ouachita Kidneyshell). The Ouachita Kidneyshell has not been documented alive during a scientific survey in the Oklahoma portion of the Verdigris River in nearly 100 years. Our observations extend the known distribution for the Western Fanshell further downstream into Oklahoma by ∼36 river km. These findings indicate an expansion in the known range and potential improvement in the populations of 2 imperiled mussel species, contrary to the prevailing global trend of mussel population decline. [ABSTRACT FROM AUTHOR]

Simple Summary: This study explores how the autumn-spawning bitterling, Acheilognathus rhombeus, reproduces and develops within its mussel host. The research highlights how these fish lay their eggs inside mussels, which then serve as a safe environment for the eggs to develop over winter. A critical phase, called diapause, allows the embryos to pause their development for about seven months, ensuring they survive the cold winter months. Once the temperature rises above 10 °C, development resumes. During this time, tiny structures on the embryos called minute tubercles help anchor them within the mussel, preventing them from being expelled prematurely. These findings provide valuable insights into the complex relationship between the bitterlings and their mussel hosts, revealing important evolutionary adaptations that aid in the reproductive success and survival of these fish. We investigated the reproductive strategies and embryonic development of Acheilognathus rhombeus (a bitterling species that spawns in autumn) within its freshwater mussel host in the Bongseo Stream, South Korea. By focusing on survival mechanisms during critical stages of embryonic development, the selective use of mussel gill demibranchs by the bitterlings and associated adaptive traits were observed over 1 year. A significant diapause phase occurs at developmental stage D, which lasts for approximately 7 months, allowing embryos to survive winter. Development resumes when the temperature exceeds 10 °C. Minute tubercles on the embryos (crucial for anchoring within the host gill demibranchs and preventing premature ejection) exhibit the largest height during diapause, and the height decreases when developmental stage E is reached, when growth resumes. Acheilognathus rhombeus embryos were observed in 30.5% of the mussels, mostly within the inner gills, thereby maximizing spatial use and oxygen access to enhance survival. These results highlight the intricate relationship between A. rhombeus and its mussel hosts, demonstrating the evolutionary adaptations that enhance reproductive success and survival. This study provides valuable insights into the ecological dynamics and conservation requirements of such symbiotic relationships. [ABSTRACT FROM AUTHOR]

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments. [ABSTRACT FROM AUTHOR]

Background: Freshwater mussels are important keystone and indicator species of aquatic ecosystems. Recent advances in sensor technology facilitate applications to individually track mussels and to record and monitor their behavior and physiology. These approaches require the attachment of sensor devices as "backpacks" to the outer shell surface. The interpretation of such data makes it necessary to understand the influence of these attachments on the horizontal and vertical movement behaviors of freshwater mussels. Over a series of mesocosm experiments, this study systematically investigated the effects of three size- and wiring-specific variants of artificially attached backpacks on the horizontal and vertical movement behavior of Anodonta anatina. Results: Across all experiments, equipping mussels with backpacks did not result in a significant influence on horizontal movement for any of the backpack variants. In contrast to this finding, the big backpacks with a high ratio between backpack volume and mussel length resulted in a significantly negative effect on vertical movement, indicating a potential for adverse effects of such devices on mussels, especially in natural settings. Conclusions: The findings of this study show that assessing the effects of attached devices on mussels requires a species-specific evaluation of potential impacts on the endpoints of interest. Especially for vertical movement patterns, selection of the smallest available devices appears mandatory. [ABSTRACT FROM AUTHOR]

In freshwater ecosystems, consumers can play large roles in nutrient cycling by modifying nutrient availability for autotrophic and heterotrophic microbes. Nutrients released by consumers directly support green food webs based on primary production and brown food webs based on decomposition. While much research has focused on impacts of consumer driven nutrient dynamics on green food webs, less attention has been given to studying the effects of these dynamics on brown food webs.Freshwater mussels (Bivalvia: Unionidae) can dominate benthic biomass in aquatic systems as they often occur in dense aggregations that create biogeochemical hotspots that can control ecosystem structure and function through nutrient release. However, despite functional similarities as filter‐feeders, mussels exhibit variation in nutrient excretion and tissue stoichiometry due in part to their phylogenetic origin. Here, we conducted a mesocosm experiment to evaluate how communities of three phylogenetically distinct species of mussels individually and collectively influence components of green and brown food webs.We predicted that the presence of mussels would elicit a positive response in both brown and green food webs by providing nutrients and energy via excretion and biodeposition to autotrophic and heterotrophic microbes. We also predicted that bottom‐up provisioning of nutrients would vary among treatments as a result of stoichiometric differences of species combinations, and that increasing species richness would lead to greater ecosystem functioning through complementarity resulting from greater trait diversity.Our results show that mussels affect the functioning of green and brown food webs through altering nutrient availability for both autotrophic and heterotrophic microbes. These effects are likely to be driven by phylogenetic constraints on tissue nutrient stoichiometry and consequential excretion stoichiometry, which can have functional effects on ecosystem processes. Our study highlights the importance of measuring multiple functional responses across a gradient of diversity in ecologically similar consumers to gain a more holistic view of aquatic food webs. [ABSTRACT FROM AUTHOR]

This study is based on a natural experiment carried out in the Biebrza National Park, Poland. The study site was a channel inhabited by Anodonta anatina, A. cygnea, Unio pictorum and U. tumidus. The deepening of the channel to restore ecosystem connectivity provided an opportunity to conduct this study. Mussels were collected before dredging, held in captivity for 48 h, measured, individually tagged and released post-dredging to the same 5-m channel sections they originated from. They were subsequently monitored for three consecutive years. Mussel survival remained high throughout the study, and no increased mortality in the year following reintroduction was observed. There was no growth retardation. Mussel mobility was low, with most individuals remaining in the same channel section in which they were released. Recolonisation patterns were consistent with the composition of mussel communities in adjacent unaffected habitats. Although dredging drastically changes mussel habitat, some characteristics: microclimate, water chemistry, nutrient availability and host fish can remain adequate. Our study shows that reintroducing mussels to the same site can serve as an effective mitigation conservation measure and can be preferable to translocation, particularly when carried out under time pressure with limited possibilities of assigning appropriate destination sites. [ABSTRACT FROM AUTHOR]

Freshwater bivalve mussels in the order Unionida are highly endangered ecosystem engineers with a parasitic lifecycle necessitating a fish host to metamorphose from larval glochidia to juvenile mussel. While many species are broadcast spawners and release a large number of glochidia into the water column, many other species have a variety of highly evolved lure mechanisms and mantle displays to attract hosts to ensure a more targeted infestation. Almost all lure mussels are found exclusively in North America, with only one European species (Unio crassus) occasionally displaying a host attraction behaviour referred to as larval spurting. Here, I present evidence that the depressed river mussel (Pseudanodonta complanata) exhibits mantle displays to attract fish to gravid mussels for a targeted infestation, the first description of mantle displays in Europe. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems and the biodiversity they support are facing unprecedented threats, exemplified by broad declines of freshwater mussels within a global biodiversity hotspot. The Rocky Mountain Ridged Mussel (Gonidea angulata) is an at-risk species in Canada, with limited information on population age structure. Maximum age of the species was found to be 50 years, by counting winter annuli and validated by isotopic oxygen analysis. Employing a Bayesian Generalized Linear Mixed Model (GLMM), results showed mussels from river habitat were predicted to have faster growth rates than mussels from lake habitats, highlighting the impact of local environmental conditions, including temperature variations, primary productivity, and water quality, on mussel growth dynamics. Of concern was the limited evidence of juvenile recruitment, with the majority of specimens potentially representing an ageing population. This pattern potentially signals an early warning of impending population decline. Our results underscore the necessity of monitoring age structure as a vital component of assessing population health of freshwater mussels and the importance of understanding local environmental conditions when determining age. [ABSTRACT FROM AUTHOR]

Freshwater mussel declines range from dramatic to subtle, but there are few methods for quantifying the extent of decline and overall assemblage health. Available assessment tools are specific to particular streams or regions and depend on untested assumptions or subjective assessments of species' tolerance to various factors. We developed a broadly applicable, objective mussel assemblage health index (MAHI). We compiled a dataset of mussel survey data from 50 streams across eastern North America and evaluated the ability of 19 candidate metrics to discriminate healthy and degraded assemblages. MAHI includes 4 metrics representing fundamental aspects of assemblage or population health (species loss, recruitment, abundance, and population growth). Metrics are scaled from 0 to 10 (representing increasing health), and the composite score is the unweighted mean of the 4 metrics. MAHI effectively discriminated healthy (median score = 8.3) and degraded (3.2) assemblages. The composite score is robust to missing values—omitting any single metric resulted in a median score change of ≤0.7. Composite scores were similar to independent scores provided by experts, but MAHI eliminates variation due to differences in individual perception or experience. MAHI can be applied to streams across eastern North America using commonly collected mussel survey data, and it may be adapted to other regions. MAHI is free of untested assumptions or subjective assessments, and it accounts for expected differences in mussel assemblages due to stream size, biogeographic region, and other intrinsic factors. MAHI will be a valuable tool for early detection of mussel declines, better understanding the causes of declines, and evaluating the effectiveness of conservation strategies and management actions. We developed a Microsoft Excel application that calculates MAHI scores, and we provide a link to that resource. [ABSTRACT FROM AUTHOR]

The risk of lampricide applications (such as 4‐nitro‐3‐[trifluoromethyl]phenol [TFM]) to nontarget fauna continues to be a concern within the Great Lakes Fishery Commission Sea Lamprey Control Program, especially among imperiled aquatic species—such as native freshwater mussels. The Grand River (Ohio, USA) is routinely treated for larval sea lampreys (Petromyzon marinus), and this river contains populations of the federally threatened mussel Obovaria subrotunda. Given this spatial overlap, information on the sensitivity of O. subrotunda to TFM is needed. Our objectives were to assess the toxicity of TFM to (1) adult Obovaria olivaria (a surrogate for O. subrotunda), (2) glochidial larvae of O. olivaria and O. subrotunda, (3) juveniles of O. olivaria and O. subrotunda, and (4) adult Percina maculata (host for O. subrotunda glochidia). In acute toxicity tests, TFM was not toxic to glochidia and adult mussels at exposure concentrations that exceed typical treatment rates. Although significant dose–response relationships were observed in hosts and juveniles, survival was ≥95% (Percina maculata), ≥93% (O. olivaria), and ≥74% (O. subrotunda) at typical treatment rates. However, the steep slope of these dose–response relationships indicates that an approximately 20% difference in the treatment level can result in nearly an order of magnitude difference in survival. Collectively, these data indicate that routine sea lamprey control operations are unlikely to acutely affect these species or their host. However, given that many mussel species are long‐lived (30–100 years), the risks posed by lampricide treatments in the Great Lakes would be further informed by research on the potential long‐term effects of lampricides on imperiled species. Environ Toxicol Chem 2024;43:1423–1430. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

North America is home to some of the most diverse freshwater mussel fauna (Mollusca: Unionidae) in the world, with the majority of mussel diversity located in the southeastern United States. Unfortunately, mussels are one of most imperiled groups in the world and species are declining across the United States. Anthropogenic habitats may function as refugia for some mussel species; however, many of these habitats are ignored during studies. The False River of Louisiana is a unique system that has separated from the Mississippi River and is dependent on an artificial canal system to maintain water levels. The canal may act as refugia for mussels during climatic events, but it is unknown whether the system can sustain mussels. To obtain an understanding of the structure and health of mussels within this anthropogenic structure, we surveyed mussels and fish at 11 sites in a section of artificial canal connected to the False River. We analyzed the mussel assemblage with regard to life history strategies and compared fish presence to known fish host use of our various mussel species. We collected 388 individuals of 13 live mussel species, with 5 additional species located as shell material. The fish assemblage consisted of 22 species of which 15 were hosts for at least one member of the mussel assemblage. The mussel assemblage primarily consisted of opportunistic species and host generalists with a few dominant species. This is, to our knowledge, the first mussel peer-reviewed mussel data reported from any portion of the False River system and the mussel assemblage appears to follow predictable trends for flashy systems noted in other rivers. Our study highlights that the False River canal system is capable of sustaining mussels and indicates that anthropogenic structures should be incorporated into future survey efforts. [ABSTRACT FROM AUTHOR]

The present work concerns the interaction between hydraulic processes and biological communities in rivers. In particular, the aim of this study is to investigate the interactions between flow dynamics and the freshwater mussels (FMs) to verify if the mussels' behavioural response to the hydrodynamic stress could be used to monitor natural extreme events in rivers. Although the influence of mussels on the kinematic characteristics of flow at the water–sediment interface was investigated by a certain number of studies, their behavioural response to flow, both in static and dynamic conditions, remains understudied. Laboratory experiments were performed in an artificial flume exposing Unio elongatulus to different values of flow discharge, both in steady and in unsteady conditions either with or without sediment transport. Mussels' behavioural responses were detected by using Hall sensor technology to measure gaping frequency, amplitude and duration, both in static conditions and under the effect of hydrodynamic stresses. Five categories of behavioural response were identified: Normal Activity (NA), Resting (Re), Transition (Tr), Adaptation (Ad) and Avoidance (Av). During NA (standard feeding and moving), FMs presented valve gaping, while during Re valves were kept constantly opened for water filtration. After a variation of flow discharge (ΔQ), FMs promptly reacted showing a transition from their normal behaviour, with constant gaping frequency (below 0.01 Hz), to higher valve gaping frequencies. The mean valves' gaping frequency increased as a function of ΔQ, and the highest values were reached in the presence of sediment transport. The mean valve opening amplitude was less sensitive to ΔQ. Its range of variation was very narrow with the highest values corresponding to the protrusion/retraction of the animals' foot to move or anchor to the substrate. The percentage of mussels responding to the discharge variation (Transition behaviour) increases with ΔQ confirming that mussels' behavioural response represents a promising tool for monitoring the occurrence of hydrodynamic stressors in fluvial systems. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Mollusca: Unionidae) play a crucial role in freshwater river environments where they live in multi-species aggregations and often serve as long-lived benthic ecosystem engineers. Many of these species are imperiled and it is imperative that we understand their basic needs to aid in the reestablishment and maintenance of mussel beds in rivers. In an effort to expand our knowledge of the diet of these organisms, five species of mussel were introduced into enclosed systems in two experiments. In the first, mussels were incubated in water from the Clinch River (Virginia, USA) and in the second, water from a manmade pond at the Commonwealth of Virginia's Aquatic Wildlife Conservation Center in Marion, VA. Quantitative PCR and eDNA metabarcoding were used to determine which planktonic microbes were present before and after the introduction of mussels into each experimental system. It was found that all five species preferentially consumed microeukaryotes over bacteria. Most microeukaryotic taxa, including Stramenopiles and Chlorophytes were quickly consumed by all five mussel species. We also found that they consumed fungi but not as quickly as the microalgae, and that one species of mussel, Ortmanniana pectorosa, consumed bacteria but only after preferred food sources were depleted. Our results provide evidence that siphon feeding Unionid mussels can select preferred microbes from mixed plankton, and mussel species exhibit dietary niche differentiation. [ABSTRACT FROM AUTHOR]

Rare earth elements (REE) are essential components of many electronic devices that could end-up in solid waste disposal sites and inadvertently released in the environment. The purpose of this study was to examine the toxicity of two heavy REEs, erbium (Er) and lutetium (Lu), in freshwater mussels Dreissena polymorpha. Mussels were exposed to 14 days to increasing concentration (10, 50, 250, and 1250 µg/L) of either Er and Lu at 15 °C and analyzed for gene expression in catalase (CAT), superoxide dismutase (SOD), metallothionein (MT), cytochrome c oxidase (CO1), and cyclin D for cell cycle. In addition, lipid peroxidation (LPO), DNA damage (DNAd), and arachidonate cyclooxygenase were also determined. The data revealed that mussels accumulated Er and Lu similarly and both REEs induced changes in mitochondrial COI activity. Er increased cell division, MT, and LPO, while Lu increased DNAd and decreased cell division. Tissue levels of Er were related to changes in MT (r = 0.7), LPO (r = 0.42), CO1 (r = 0.69), and CycD (r = 0.31). Lu tissue levels were related to changes in CO1 (r = 0.73), CycD (r = − 0.61), CAT (r = 0.31), DNAd (r = 0.43), and SOD (r = 0.34). Although the lethal threshold was similar between Er and Lu, the threshold response for LPO revealed that Er produced toxicity at concentrations 25 times lower than Lu suggesting that Er was more harmful than Lu in mussels. In conclusions, the data supports that the toxicity pattern differed between Er and Lu although they are accumulated in the same fashion. [ABSTRACT FROM AUTHOR]

The ASTM International standard test method for freshwater mussels (E2455‐13) recommends 4‐week toxicity testing with juveniles to evaluate chronic effects on survival and growth. However, concerns remain that the method may not adequately address the sensitivity of mussels to longer term exposures (>4 weeks), particularly in relation to potential reproductive impairments. No standard method directly evaluates toxicant effects on mussel reproduction. The objectives of the present study were to (1) evaluate toxicity endpoints related to reproduction in fatmucket (Lampsilis siliquoidea) using two common reference toxicants, potassium chloride (KCl) and nickel (Ni); (2) evaluate the survival and growth of juvenile fatmucket in standard 4‐week and longer term (12‐week) KCl and Ni tests following a method refined from the standard method; and (3) compare the sensitivity of the reproductive endpoints with the endpoints obtained from the juvenile mussel tests. Reproductive toxicity tests were conducted by first exposing female fatmucket brooding mature larvae (glochidia) to five test concentrations of KCl and Ni for 6 weeks. Subsamples of the glochidia were then removed from the adults to determine three reproductive endpoints: (1) the viability of brooded glochidia; (2) the viability of free glochidia in a 24‐h exposure to the same toxicant concentrations as their mother; and (3) the success of glochidia parasitism on host fish. Mean viability of brooded glochidia was significantly reduced in the high KCl concentration (26 mg K/L) relative to the control, with a 20% effect concentration (EC20) of 14 mg K/L, but there were no significant differences between the control and any Ni treatment (EC20 > 95 µg Ni/L). The EC20s for viability of free glochidia after the additional 24‐h exposure and parasitism success were similar to the EC20s of brooded glochidia. The EC20s based on the most sensitive biomass endpoint in the 4‐week juvenile tests were 15 mg K/L and 91 µg Ni/L, similar to or greater than the EC20s from the reproductive KCl and Ni tests, respectively. When exposure duration in the juvenile tests was extended from 4 to 12 weeks, the EC20s decreased by more than 50% in the KCl test but by only 8% in the Ni test. Overall, these results indicate that a standard 4‐week test with juvenile mussels can prove effective for estimating effects in chronic exposures with different life stages although a longer term 12‐week exposure with juvenile mussels may reveal higher sensitivity of mussels to some toxicants, such as KCl. Environ Toxicol Chem 2024;43:1097–1111. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

The loose‐equilibrium concept (LEC) predicts that ecological assemblages change transiently but return towards an earlier or average structure. The LEC framework can help determine whether assemblages vary within expected ranges or are permanently altered following environmental change.Long‐lived, slow‐growing animals typically respond slowly to environmental change, and their assemblage dynamics may respond over decades, which transcends most ecological studies. Unionid mussels are valuable for studying dynamics of long‐lived animals because they can live >50 years and occur in dense, species‐rich assemblages (mussel beds). Mussel beds can persist for decades, but disturbance can affect species differently, resulting in variable trajectories according to differences in species composition within and among rivers.We used long‐term data sets (10–40 years) from seven rivers in the eastern United States to evaluate the magnitude, pace and directionality of mussel assemblage change within the context of the LEC.Site trajectories varied within and among streams and showed patterns consistent with either the LEC or directional change. In streams that conformed to the LEC, rank abundance of dominant species remained stable over time, but directional change in other streams was driven by changes in the rank abundance and composition of dominant species.Characteristics of mussel assemblage change varied widely, ranging from those conforming to the LEC to those showing strong directional change. Conservation approaches that attempt to maintain or create a desired assemblage condition should acknowledge this wide range of possible assemblage trajectories and that the environmental factors that influence those changes remain poorly understood. [ABSTRACT FROM AUTHOR]

Freshwater mussel populations are in sharp decline and are considered to be one of the most imperilled groups globally. Consequently, the number of captive breeding programmes has increased rapidly in recent years, coupled with subsequent reintroductions/population reinforcements to reverse these declines. The outcomes of mussel conservation translocations are seldom reported in the primary literature, hindering opportunities for learning and for population recovery at pace. Here, we describe the methods employed to carry out a successful conservation translocation of the freshwater pearl mussel (Margaritifera margaritifera) in a declining population in northwest England. Following a small-scale pilot release in 2017, four release sites were identified for a population reinforcement of over 1300 tagged mussels in 2021. Monitoring during 2022 showed high levels of retention of juveniles at three out of the four release sites, despite the occurrence of a significant flood event during October 2021. Subsequent releases of 1100 juveniles were carried out across the three successful sites in 2023. Ongoing and regular monitoring is essential in order to provide data on the longer-term fate of propagated juveniles in the wild. This will allow for adaptive management of release activities in this river. These data will be useful to design conservation translocation strategies for other imperilled pearl mussel populations in the UK and throughout Europe. [ABSTRACT FROM AUTHOR]

Historically, 23 freshwater mussel species have been documented from the Buffalo National River (BNR), a 246 km, free-flowing river in northern Arkansas. The potential threats to BNR include land use/land cover changes, eutrophication, recreation, physical habitat changes, and various climate change-related effects. Twelve quantitative mussel bed sites were established and then sampled using a stratified random sampling protocol to evaluate the long-term changes between 2006 and 2020–2021 in population and assemblage characteristics. We compared (1) overall mussel bed persistence, sampling confidence levels and study-wide relative abundances, and compared species' size and size-frequency distributions; (2) 10 overall site assemblage variables using paired t-tests; (3) site-level mean density, richness, and diversity indices using pair-wise Mann–Whitney U statistics; and (4) assemblage composition using Non-Metric Multidimensional Scaling. The major findings included the following: (1) sampling efforts based on a targeted 80% confidence level appears relatively robust, (2) BNR mussel assemblage composition and structure were relatively stable (however, small mussel bed persistence is a concern), (3) 7 of 23 sites were outliers based on freshwater mussel composition and habitat characteristics, and (4) assemblage composition changed with three species declining (Actinonaias ligamentina, Lasmigona costata, and Ptychobranchus occidentalis) and four species increasing (Cambarunio hesperus, Cyclonaias tuberculata, Eurynia dilatata, and Venustaconcha pleasii) between monitoring events. [ABSTRACT FROM AUTHOR]

210Po is a significant source of ionizing radiation that people are exposed to through food globally. This paper presents the wide range of accumulation level of 210Po in the organs of two species of shellfish including freshwater mussel (Sinanodonta jourdyi) and golden apple snail (Pomacea canaliculata), common freshwater species in Vietnam. There was a significant correlation between 210Po activity in muscle to their mass and size of freshwater mussels. In contrast, there was no relation between other organs of both species with their mass and size. The annual effective dose due to consumption of freshwater mussels ranged from 68.7 to 291 μSv year−1 with a mean value of 138 μSv year−1 for muscle and from 321 to 4560 μSv year−1 with a mean value of 1422 μSv year−1 for the hepatopancreas. Meanwhile, the AED for golden apple snail was recorded to be higher with values ranging from 105 to 2189 μSv year−1 with mean value of 673 μSv year−1 for muscle and from 468 to 4155 μSv year−1 with a mean value of 2332 μSv year−1 for hepatopancreas. Thus, the consumption of these two types of shellfish is considered relatively safe, but the hepatopancreas gland must be removed before processing. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Order Unionoida) can provide crucial ecological functions and services. However, many of them are endangered worldwide due to local extirpation and reproductive failure, which emphasizes the importance of mussel life cycle monitoring, including reproduction. Buldowskia iwakawai (Suzuki, 1939) is one such species native to the Ishikari floodplain oxbow lakes where its reproductive failure was recently reported. In this study, a species-specific environmental DNA (eDNA) assay was developed to monitor B. iwakawai abundance and winter reproduction in the laboratory and natural environment simultaneously even at times when natural lakes are covered by ice. A positive CPUE-eDNA correlation was observed across all the 14 lakes sampled prior to ice cover formation. The eDNA concentration significantly differed between gravid and non-gravid mussels in relation to their metabolic-rate differences in laboratory experiments, but the eDNA concentration increase was not detected in the intensively monitored lakes during the glochidia release period. PCR inhibition in natural water has been suggested, and reducing its effects combined with appropriate seasonal contexts has the potential to improve the applicability of this method. This research sheds new light on the applicability of the eDNA assay for monitoring mussel reproductive activities throughout their life cycle including the winter season. [ABSTRACT FROM AUTHOR]

A significant part of freshwater mussel populations has strongly declined and many species are severely threatened nowadays. Captive breeding programs often form a central part of conservation strategies. As the life cycles of many mussel species include an obligate parasitic phase, host fish health is a crucial component of successful mussel breeding efforts. However, information about the safe application of fish therapeutants in mussel captive breeding is scarce. This article summarizes information about practical experiences in Europe. In total, eight different therapeutants were used to treat infestations of eight pathogens. Treatment success varied depending on pathogen and prevalence when treatments were initiated. Mussels did not seem to be affected by treatments, especially as long as they remained encysted. In a second step, Virkon S was applied to treat a fungal infection in tanks with brown trout (Salmo trutta) carrying encysted freshwater pearl mussel (Margaritifera margaritifera) glochidia and to disinfect juvenile mussel rearing containers. In both cases, mussels were not harmed and treated fish fully recovered. Results indicate that certain therapeutants can be used safely and successfully at different stages of breeding cycles. Nevertheless, there is still a lack of standard protocols, which would improve efficiency and the safety of treatments. [ABSTRACT FROM AUTHOR]

Freshwater mussel species regularly co‐occur in streams forming assemblages, but the extent of shared versus unique instream habitat features that contribute to their distribution and abundance is poorly understood. In Massachusetts, a rare species, Alasmidonta varicosa, is often found with four other species: Alasmidonta undulata, Strophitus undulatus, Margaritifera margaritifera, and Elliptio complanata, yet variation in species composition within assemblages raises questions of potential species‐specific habitat associations. Identifying species‐level habitat information is critical at a spatial scale that malacologists can use to identify translocation or restoration areas.This study investigated whether species abundance varied by mesohabitat type (riffle, run, dam pool, scour pool), instream habitat characteristics, and within‐reach location (centre versus edge). From 2016 to 2019, freshwater mussel surveys were conducted in nine streams across Massachusetts and associated habitat information was collected.Species abundances were similar across mesohabitat types. Elliptio complanata was the exception, whereby higher abundances occurred in runs and dammed pools than in riffles. Unique species relationships with habitat existed for M. margaritifera with macroalgae and emergent vegetation, and A. varicosa with heterogeneous substrate. Flow transitions, such as depositional areas that create heterogeneous substrates, may provide habitats for A. varicosa.Most mussel species were distributed with higher abundance in the river centre than the edge; E. complanata was the only species with a higher abundance at the river edge. Locations with high abundance varied based on unique relationships with pebble heterogeneity (A. varicosa), depth (A. undulata), large wood (A. undulata), and canopy closure (E. complanata). Including physical characteristics in a holistic assessment of habitat that incorporates fish and landscape attributes may further an understanding of river reaches that best support translocated and propagated freshwater mussels. [ABSTRACT FROM AUTHOR]

Many freshwater mussel species require fish hosts for successful reproduction; these relationships can be highly specialized and variable across mussel species. Most mussel host-identification studies have occurred in a laboratory setting and may miss important behavioral and spatial aspects of the mussel-host relationship. As such, conducting in situ evaluations of fish host use by mussel glochidia can provide additional information regarding fish-mussel relationships in the wild. However, in situ mussel-host examinations are rare, and few have been completed along the southern Atlantic slope of the United States. The goal of our study was to examine potential host use and glochidial-release timing in a small stream in South Carolina. Our objectives were to identify fish species used as mussel hosts, examine differences in the prevalence and intensity of infestations among host species, and quantify the effects of water temperature and stream flow on the probability of fish infestation. We examined wild-caught fishes for the presence of glochidial infestations in Sleepy Creek, a small tributary to Stevens Creek in the Savannah River basin of south-central South Carolina. We inspected a total of 822 individual fishes of 14 species and detected glochidia on 92 individuals of 5 fish species. Mean intensity of infestations varied from 7 to 45 glochidia per fish, but intensities did not differ significantly among fish species. Water temperatures and fish total length had significant positive effects on the probability of glochidial infestation. Highest glochidia prevalence occurred toward the end of our study at warmer temperatures and on mid-length fishes. Our study highlights the potential of in situ studies and DNA metabarcoding for identifying host use of wild glochidia. [ABSTRACT FROM AUTHOR]

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Freshwater mussels are globally imperilled, which is attributed to their sensitivity to changes in streamflow and temperature. The Black River in south‐eastern New Mexico, USA, harbours a stronghold population of the federally endangered unionid Popenaias popeii (Texas hornshell). Decreasing discharge and elevated water temperatures are considered the primary factors responsible for the species' decline. However, the impact of these factors has not been quantified directly, which may hinder conservation efforts.The upper thermal tolerances (LT05 and LT50) of Black River P. popeii larvae (glochidia) and newly transformed juveniles were evaluated. Individuals were acclimated to 27°C and then immersed at five experimental temperatures (28, 30, 32, 34 and 36°C) for 24 h (glochidia) or 96 h (juveniles). The thermal tolerances of P. popeii and its presumed host fishes were then overlain onto in situ water temperature and discharge data to determine thermal exceedances in the past 15 years. Temperature was hindcast back to 2007 using machine learning (random forest model) and coupled with discharge.For glochidia, LT05 was exceeded frequently (41%) and LT50 was exceeded occasionally (13%) during spring and summer periods, whereas juvenile thresholds were never exceeded. Upper continuous duration above threshold (UCAT) analysis revealed periods of catastrophic high temperature, which were used to determine discharge bottlenecks.This study demonstrates how laboratory‐derived physiological thresholds can be used in conjunction with environmental data to evaluate the hydrological needs of aquatic organisms, which is useful in efforts to maintain flow regimes that protect native ecosystems. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the impact of natural river floods on biotic communities. To this purpose, we used freshwater mussels (FMs), recognized as one of the most reliable bioindicators in aquatic environments. A well-established valvometry technique was applied to measure the FMs valve gaping behaviour, considering both gaping amplitude and frequency. The mussels have been employed in two distinct configurations, either free to move or stuck on vertical bars. We performed experiments in a laboratory flume and in the Paglia River (Italy). The FMs valve gaping movement was first recorded, then the continuous wavelet transform (CWT) analysis was applied to the signals to get the time-dependent frequency of the signals. Laboratory experiments allowed to assess to what extent stuck mussels react differently than free mussels to abrupt increases in flow conditions. Subsequently, we examined the response of thirteen stuck mussels installed in real riverine conditions during a moderate flood occurred on March 31, 2022, with a rapid increase of the water level. The experimental results demonstrate that stuck mussels produce signals that are more consistent and easier to interpret compared to free mussels, primarily due to the reduced number of features resulting from movement constraints. The stuck mussels in the field showed a sharp and timely change of valve gaping frequency as the flood ramped up, thus confirming the findings in the laboratory. The results highlight the effectiveness of using FMs as bioindicators for assessing the impact of floods on the aquatic ecosystem, and the utility of CWT as a suitable signal processing tool for analyzing valvometric time series. These findings provide a pathway towards the integration of FMs valvometry and CWT for the development of operational real-time Biological Early Warning Systems (BEWS) aimed at the monitoring and safeguarding of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

We investigated an interaction between bitterlings and a parasitic leech Hemiclepsis kasmiana in freshwater mussel hosts. We found that leeches fed on bitterling eggs and embryos; this may exert a considerable negative effect on bitterling fitness. Host choices by females of three bitterling species may be differently affected by the presence of leeches within mussels; Tanakia limbata apparently avoided laying eggs in infested mussels while T. lanceolata and Acheilognathus rhombeus did not. Our novel findings suggest that relationships between the parasitic leech and the host mussel may be context dependent. [ABSTRACT FROM AUTHOR]

Animals are a critical component of biogeochemical cycles. While animal mediated fluxes of nutrients and energy have received considerable attention, the impacts of these fluxes on microbial community structure and function are comparatively understudied. Here, we investigated if freshwater mussel influences on biogeochemical cycling in stream sediment are accompanied by changes in sediment microbial community composition and ecoenzymatic activity, and if these relationships change under different nutrient regimes.We predicted that mussel effects on ecosystem function are reflected by modified sediment microbial communities. We hypothesized that if changes in either sediment ecoenzymatic function or microbial community composition are driven by mussel‐derived nutrient amendments, we should see muted changes in microbial community assemblages or function when a given nutrient is abundant. However, if microbial communities and function are influenced by other mussel functions, then we should see uniform changes regardless of nutrient availability.We transplanted freshwater mussels and natural river sediment to flow‐through mesocosms and monitored changes in microbial community composition over 1 week. Our results indicate that mussels always changed sediment microbial community composition, but the way communities changed was dependent on ambient nutrient concentrations.On the final day we measured the activity of ecoenzymes known to correlate to microbial function and nutrient availability. Mussels homogenized the stoichiometric ratios of ecoenzyme activities, indicating a consistent function of sediment microbes associated with freshwater mussels. Our results suggest that mussels may promote functional redundancy in sediment microbial communities and highlight the importance of animals in controlling biogeochemical transformations under changing nutrient conditions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Freshwater mussels are one of the most diverse and critically endangered organismal groups in the world. In North America, many of the ∼300 species are imperiled to some degree, and numerous states, including Illinois, have instituted surveys and safeguards to protect their remaining mussel resources. In Illinois, the status of many mussel species is unknown, and additional efforts are needed to determine the health of rare and endangered mussels. The Rock River system was historically a stronghold for mussels in Illinois; however, studies over the last decade are lacking. To obtain current data on the health and status of mussels within a portion of the Rock River, we conducted survey efforts throughout the upper Rock River. We sampled mussels semi-quantitatively at 30 sites using bank-to-bank transects in July of 2021 to determine whether rare and endangered species were still extant. We also examined the abundances of species currently considered common and assessed shell-length data to determine the overall viability of the mussel fauna. We surveyed a total of 4360 m of the river and obtained 2506 live mussels of 19 species. The assemblage consisted primarily of Potamilus ohiensis (Pink Papershell) and Cyclonaias pustulosa (Pimpleback), and approximately half the assemblage consisted of recent recruits (juveniles). We collected live Cyclonaias nodulata (Wartyback), Cyclonaias tuberculata (Purple Wartyback), and Truncilla donaciformis (Fawnsfoot), all Illinois or Wisconsin state-listed species. The Purple Wartyback consisted of 2 cohorts and are the first live individuals recorded from the Rock River since the late 1980s. Furthermore, the presence of numerous juveniles indicates successful reproduction and recruitment for multiple species. Continued work on managing stream habitats is vital to protecting and reinforcing their remaining diversity, and the upper Rock River warrants further protections. [ABSTRACT FROM AUTHOR]

Freshwater mussels are declining throughout their range. Their important ecological functions along with insufficient levels of natural recruitment have prompted captive breeding for population augmentation and questions about the usefulness and applicability of such measures.This article reviews the current state of captive breeding and rearing programmes for freshwater mussels in Europe. It considers the various species, strategies, and techniques of propagation, as well as the different levels of effort required according to rearing method, highlighting the key factors of success.Within the last 30 years, 46 breeding activities in 16 European countries have been reported, mainly of Margaritifera margaritifera and Unio crassus. Some facilities propagate species that are in a very critical situation, such as Pseudunio auricularius, Unio mancus, and Unio ravoisieri, or multiple species concurrently. In some streams, the number of released captive‐bred mussels already exceeds the size of the remaining natural population.Rearing efforts range from highly intensive laboratory incubation to lower intensity methods using in‐river mussel cages or silos. Most breeding efforts are funded by national and EU LIFE(+) grants, are well documented, and consider the genetic integrity of the propagated mussels. Limited long‐term funding perspectives, the availability of experienced staff, water quality, and feeding/survival during early life stages are seen as the most important challenges.Successful captive breeding programmes need to be combined with restoration of the habitats into which the mussels are released. This work will benefit from an evidence‐based approach, knowledge exchange among facilities, and an overall breeding strategy comprising multiple countries and conservation units. [ABSTRACT FROM AUTHOR]

The United States of America has a diverse collection of freshwater mussels comprising 301 species distributed among 59 genera and two families (Margaritiferidae and Unionidae), each having a unique suite of traits. Mussels are among the most imperilled animals and are critical components of their ecosystems, and successful management, conservation and research requires a cohesive and widely accessible data source. Although trait-based analysis for mussels has increased, only a small proportion of traits reflecting mussel diversity in this region has been collated. Decentralized and non-standardized trait information impedes large-scale analysis. Assembling trait data in a synthetic dataset enables comparison across species and lineages and identification of data gaps. We collated data from the primary literature, books, state and federal reports, theses and dissertations, and museum collections into a centralized dataset covering information on taxonomy, morphology, reproductive ecology and life history, fish hosts, habitats, thermal tolerance, geographic distribution, available genetic information, and conservation status. By collating these traits, we aid researchers in assessing variation in mussel traits and modelling ecosystem change. [ABSTRACT FROM AUTHOR]

The origin of the fauna of Beringia is a notable biogeographical puzzle. Large mussels of the genus Beringiana inhabit both Northeast Asia and the northwestern part of North America and thus provide an important model to investigate the paleobiogeography of Beringia and the past and current intercontinental species exchanges. Data on Beringiana distribution, morphology, genetics, and taxonomy are fragmentary or questionable. In this study, we summarized the data on its distribution in Northeast Asia, performed genetic analysis (cox1), and studied the variation in the shell morphology in samples from four isolated populations, including the putative sympatric species. Over ten large enclaves of Beringiana are currently known in Northeast Asia (east to the Verkhoyansk Range), mostly in the lower reaches of large rivers in northeastern Yakutia, Kamchatka, Magadan Oblast, and Khabarovsk Krai. These enclaves are far apart (several hundreds of kilometers) because the mussel is associated with muddy sand or pebbly sand bottom substrates and spreads through its glochidia, which are parasitic on the fish. Shell morphology can be highly variable even in a single population, overlapping the diagnoses of several Beringiana species (which are currently not recognized as valid). Our analysis of the cox1 sequence in four populations identified all individuals as B. beringiana. We evaluated the possible current and probable Late Pleistocene–Early Holocene freshwater and marine pathways of B. beringiana dispersal through the area of former Beringia, including the current intercontinental migration of glochidia on fish. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Freshwater mussels are among the most imperiled freshwater taxa, and translocation of these endangered species is one option for conservation. However, the long-term success of translocations is difficult to determine, in part because the amount of suitable habitat for a translocated species is often not known. Two federally endangered freshwater mussel species, the Northern Riffleshell Epioblasma rangiana (Lea, 1837) and the Clubshell Pleurobema clava (Lamarck, 1819), were recently translocated to the Middle Fork and Salt Fork of the Vermilion River in East Central Illinois, USA; however, the total amount of suitable habitat in both rivers remains unknown. To identify potential suitable habitat for these mussels in the Middle Fork and Salt Fork of the Vermilion River, we sampled 79 sites for surrogate mussel species of E. rangiana and P. clava along with their host fishes. We investigated habitat suitability by modeling presence/absence and abundance of surrogate mussel species to determine the landscape variables most strongly associated with surrogate mussel species presence/absence and abundance. We used these model results to create a habitat suitability index. We then validated our model predictions using timed searches in y 2 of our study. Our results indicate there may be more suitable habitat than previously believed throughout both rivers and that ample habitat is available to support large populations of mussels. Our approach also demonstrates how landscape variables can be used to successfully identify potential sites for future translocations. [ABSTRACT FROM AUTHOR]

The biodiversity‐disease relationship states that increased species richness leads to lower pathogen pressure (i.e. the dilution effect), an effect that erodes with biodiversity loss. However, whether losses of the dilution effect can trigger extinction cascades remains largely unexplored.To explore this idea, we consider declines in freshwater mussels, on average the most threatened non‐marine group of organisms in the world. We argue that anthropogenically stimulated declines in mussel richness amplify pathogens in remaining species. Pathogen amplification triggers further local losses in both mussel abundance and richness, explaining the observed so‐called "enigmatic" declines in freshwater mussels.Vulnerable communities could become trapped in cycles of pathogen amplification and host decline. We highlight knowledge gaps and provide key steps to assess the likelihood of this occurring; these key steps are applicable to any host group.Policy implications. Our argument constitutes a testable hypothesis that may explain richness or abundance declines in previously intact communities. We provide further impetus for the consideration and preservation of diversity at a local scale and show that effective conservation requires integration of both host and parasite ecology. [ABSTRACT FROM AUTHOR]

Freshwater mussels are one of the most imperiled groups of organisms in the world, and more than 30 species have gone extinct in the last century. While habitat alteration and destruction have contributed to the declines, the role of disease in mortality events is unclear. In an effort to involve veterinary pathologists in disease surveillance and the investigation of freshwater mussel mortality events, we provide information on the conservation status of unionids, sample collection and processing techniques, and unique and confounding anatomical and physiological differences. We review the published accounts of pathology and infectious agents described in freshwater mussels including neoplasms, viruses, bacteria, fungi, fungal-like agents, ciliated protists, Aspidogastrea, Digenea, Nematoda, Acari, Diptera, and Odonata. Of the identified infectious agents, a single viral disease, Hyriopsis cumingii plague disease, that occurs only in cultured mussels is known to cause high mortality. Parasites including ciliates, trematodes, nematodes, mites, and insects may decrease host fitness, but are not known to cause mortality. Many of the published reports identify infectious agents at the light or ultrastructural microscopy level with no lesion or molecular characterization. Although metagenomic analyses provide sequence information for infectious agents, studies often fail to link the agents to tissue changes at the light or ultrastructural level or confirm their role in disease. Pathologists can bridge this gap between identification of infectious agents and confirmation of disease, participate in disease surveillance to ensure successful propagation programs necessary to restore decimated populations, and investigate mussel mortality events to document pathology and identify causality. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Unionida) are globally imperiled, in part due to largely unexplained mass mortality events (MMEs). While recent studies have begun to investigate the possibility that mussel MMEs in the Eastern USA may be caused by infectious diseases, mussels in the Western USA have received relatively little attention in this regard. We conducted a two-year epidemiologic investigation of the role of viruses in ongoing MMEs of the Western pearlshell (Margaritifera falcata) and the Western ridged mussel (Gonidea angulata) in the Chehalis River and Columbia River watersheds in the Western USA. We characterized viromes of mussel hemolymph from 5 locations in 2018 and 2020 using metagenomic methods and identified 557 viruses based on assembled contiguous sequences, most of which are novel. We also characterized the distribution and diversity of a previously identified mussel Gammarhabdovirus related to pathogenic finfish viruses. Overall, we found few consistent associations between viruses and mussel health status. Variation in mussel viromes was most strongly driven by location, with little influence from date, species, or health status, though these variables together only explained ~1/3 of variation in virome composition. Our results demonstrate that Western freshwater mussels host remarkably diverse viromes, but no single virus or combination of viruses appears to be associated with morbidity or mortality during MMEs. Our findings have implications for the conservation of imperiled freshwater mussels, including efforts to enhance natural populations through captive propagation. [ABSTRACT FROM AUTHOR]

The elevated use of salt as a de-icing agent on roads in Canada is causing an increase in the chloride concentration of freshwater ecosystems. Freshwater Unionid mussels are a group of organisms that are sensitive to increases in chloride levels. Unionids have greater diversity in North America than anywhere else on Earth, but they are also one of the most imperiled groups of organisms. This underscores the importance of understanding the effect that increasing salt exposure has on these threatened species. There are more data on the acute toxicity of chloride to Unionids than on chronic toxicity. This study investigated the effect of chronic sodium chloride exposure on the survival and filtering activity of two Unionid species (Eurynia dilatata, and Lasmigona costata) and assessed the effect on the metabolome in L. costata hemolymph. The concentration causing mortality after 28 days of exposure was similar for E. dilatata (1893 mg Cl−/L) and L. costata (1903 mg Cl−/L). Significant changes in the metabolome of the L. costata hemolymph were observed for mussels exposed to non-lethal concentrations. For example, several phosphatidylethanolamines, several hydroxyeicosatetraenoic acids, pyropheophorbide-a, and alpha-linolenic acid were significantly upregulated in the hemolymph of mussels exposed to 1000 mg Cl−/L for 28 days. While no mortality occurred in the treatment, elevated metabolites in the hemolymph are an indicator of stress. [ABSTRACT FROM AUTHOR]

The basic knowledge of freshwater bivalves in the Unionida in some regions of the world is still limited, hindering potential conservation efforts, including in Vietnam. A subset of these mussels, the freshwater bivalve tribe Anodontini, is especially difficult to properly identify morphologically due to intraspecific shell similarity. This study aims to define the species of Anodontini in Vietnam and describe their evolutionary relationships and distributions by estimating phylogenies and analyzing collected specimens. The Anodontini are represented in Vietnam by five species divided among three genera: Sinanodonta, Cristaria, and Pletholophus. Sinanodonta woodiana, a large species complex, is represented in Vietnam by Sinanodonta jourdyi. Cristaria is confirmed to include the widespread Cristaria plicata and substantiates the validity of Cristaria truncata. Finally, Pletholophus is here recognized as distinct from Cristaria, containing two species in Vietnam, Pletholophus tenuis, and a species new to science. Our study is an important baseline for future studies on Vietnamese freshwater mussels and highlights the importance of surveys, molecular work, and taxonomic expertise to describe the biodiversity of understudied regions. [ABSTRACT FROM AUTHOR]

Freshwater mussels are a globally diverse and fundamental group in aquatic ecosystems. However, 65% of freshwater mussel species have become endangered over the past century and 10% of them are already extinct. Natural population preservation and restoration efforts have been expedited, but the complicated life history of this taxon presents many challenges since species‐specific ecology involved in restoration projects is often poorly understood.Lampsilis cardium is an imperilled freshwater mussel in Nebraska, USA. A reintroduction project has been carried out to restore L. cardium populations among three streams in Nebraska, during autumn 2016 and summer 2017. A 2‐year mark–recapture study was used to determine habitat, timing and size‐at‐introduction effects on mussel survival and growth following introduction. Water quality and habitat parameters were seasonally recorded from each site to assess potential effects on mussel growth and survival.The highest daily growth rates of L. cardium ranged between 145 and 185 μm d−1, whereas the lowest daily growth rates observed were ∼88–107 μm d−1, with the greater rate of shell growth always recorded for those individuals introduced in spring and lower for those individuals introduced in summer or autumn. Survival models indicated that mussels were most susceptible to mortality immediately following introduction in spring, whereas size at introduction had almost no effect on survival. At each site, habitat parameter measurements recorded during different seasons indicated that calcium availability, water temperatures, water depth and water quality may contribute to differences in growth and survival rates.Survival rate estimation and population growth predictions are essential knowledge to understand population dynamics; this study provides useful information and a framework for management decisions that may influence L. cardium population dynamics, such as identifying more suitable habitats and introduction times not only for this species but also other similar unionids. [ABSTRACT FROM AUTHOR]

Elevated concentrations of potassium (K) often occur in effluents from wastewater treatment plants, oil and gas production operations, mineral extraction processes, and other anthropogenic sources. Previous studies have demonstrated that freshwater mussels are highly sensitive to K in acute and chronic exposures, and that acute toxicity of K decreases with increasing water hardness. However, little is known about the influence of hardness on the chronic toxicity of K. The objective of our study was to evaluate the chronic toxicity of K (tested as KCl) to a commonly tested unionid mussel (fatmucket, Lampsilis siliquoidea) at five hardness levels (25, 50, 100, 200, and 300 mg/L as CaCO3) representing most surface waters in the United States. Chronic 28‐day K toxicity tests were conducted with 3‐week‐old juvenile fatmucket in the five hardness waters using an ASTM International standard method. The maximum acceptable toxicant concentrations (geometric mean of the no‐observed‐effect concentration and the lowest‐observed‐effect concentration) increased from 15.1 to 69.3 mg K/L for survival and from 15.1 to 35.8 mg K/L for growth (length and dry wt) and biomass when water hardness was increased from 25 mg/L (soft) to 300 mg/L (very hard). These results provide evidence to support water hardness influence on chronic K toxicity to juvenile fatmucket. However, the chronic effect concentrations based on the more sensitive endpoint (growth or biomass) increased only 2.4‐fold from the soft water to the very hard water, indicating that water hardness had a limited influence on the chronic toxicity of K to the mussels. These results can be used to establish chronic toxicity thresholds for K across a broad range of water hardness and to derive environmental guideline values for K to protect freshwater mussels and other organisms. Environ Toxicol Chem 2023;42:1085–1093. Published 2023. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Hypotheses relating genomic diversity to community attributes such as abundance and species diversity attract attention from a wide and varied audience because their applications are twofold. First, testing such hypotheses can further a theoretical—and hopefully generalizable—understanding of the forces that assemble communities and create observed patterns of biodiversity. Second, relationships that hold true could ease the burden of data collection for conservation or other urgent applications; for example, a strong correlation between species diversity and genetic diversity could make it possible to use one as a proxy for the other, and focus limited resources on measuring the easier of the two without sacrificing information gained. In a From the Cover article in this issue of Molecular Ecology, Bucholz et al. (2023) explore the relationships between within‐species genomic diversity, community relative abundance and community species richness, testing three types of ecological hypotheses in the freshwater mussel communities of the southeastern United States. They find positive relationships between mussel density and species richness, and between genomic diversity within a species and density of that species, but no robust support for the expectation of correlated genomic and species diversity. Their analyses highlight the among‐species variability in relationships among these different levels of organization and also the complex ways in which interactions with the broader ecosystem (i.e. unionid mussels require fish hosts for maturation) affect these quantitative relationships, nonetheless pushing forward into the important frontier of community‐wide genomic assessment for theoretical and conservation applications. [ABSTRACT FROM AUTHOR]