Freshwater Mussels Research Articles

Genome-wide association analysis reveals genetic architecture of growth and inner shell color traits in freshwater pearl mussel Hyriopsis cumingii (Lea 1852)

Triangle sail mussel (Hyriopsis cumingii, Lea 1852) is the most important freshwater pearl mussel in China. Growth traits of host mussels and inner shell color traits of donor mussels are critical determinants for pearl size and color. In this study, we performed GWAS analysis to explore the genetic architecture of growth and inner shell color traits. Using genotype by sequencing (GBS) technique, we obtained 80,562 SNPs from a total dataset of 463 mussels, based on these data, we found weak genetic relationship (−0.1–0.4) and rapid LD decay rate among the population. Moreover, GWAS analysis identified 12 growth-related significant SNPs and 29 inner shell color related significant SNPs. Five of the 12 SNPs linked to growth traits were validated to be credible SNPs in a new population. Cyclin, SNF, PMP22, CPED1, F-box and APC/C genes were found to be significantly associated with growth traits, which may influence the growth and development of H. cumingii by regulating cell mitosis, mantle epithelial tissue activity, and Ca2+ absorption and transport capacity. Notably, redness a* showed an obvious aggregation peak in chromosome 17, indicating that this region may be closely related to the inner shell color. Furthermore, three causal genes in chromosome 17, HSP78, MAS and PKS are inferred to be the key genes on color formation of purple inner shell. These results provide some new insights into the genetic basis and physiological regulation mechanism of growth and inner shell color traits in H. cumingii. However, detailed functional identification and regulation mechanism analysis merits more investigation.

A new superfamily of freshwater mussels Deccanoidea nov. (Mollusca: Unionida) from an intertrappean deposit of Saurashtra province (Gujarat state, western India): An example of disjunct distribution

The Cretaceous-Palaeogene intertrappean deposits of the Deccan Volcanic Province of India comprise vertebrate, invertebrate and plant fossils of the dominantly continental realm. A 3–4 m thick shaly-sandstone lacustrine intertrappean sequence of Early Palaeogene (Palaeocene-Early Eocene) Bamanbor Formation, Chotila Basin (Saurashtra province, Gujarat State, western India) has yielded a collection of molluscans (bivalve and few gastropods) fauna. High-resolution digital photography and radiography of the recovered bivalves allowed us to gain detailed inferences on shell morphology. In a taxonomical context, we herein propose a new unionid molluscan superfamily Deccanoidea nov. represented by a single new family Deccanoidae nov. that includes two new subfamilies, that is, Deccanoinae nov. (represented by two new genera Deccanoida gen. nov. [including four new species: D. conrugis sp. nov., D. aleta sp. nov., and D. costaria sp. nov.] and Bamanboria gen. nov. [including one new species Bamanboria oblongis gen. et sp. nov.] and Chotiloinae nov. [represented by one new genus Chotilia gen. nov. and three new species: Chotilia trappeansis sp. nov., C. tuberculata sp. nov. and C. deccanensis sp. nov.]). Inorganic geochemistry of host (unionid-yielding) lithologies reveals oxic-freshwater conditions, humid-climate and moderate rainfall. The data on historical biogeography reveals that the Indian subcontinent hosted unionids during the late Cretaceous; however, the presence of new (at family/generic level) unionid fauna during the Early Palaeogene (Palaeocene-Early Eocene) in India indicates changes in the geographic position and ecologic condition linked to northward drift and lava outpouring, respectively. A disjunct distribution of unionid fauna in the erstwhile Gondwanan continents and insular India during the Cretaceous-Palaeogene interval can be explained in terms of both vicariance and dispersal.

Quantifying Effects and Ingestion of Several Pristine Microplastics in Two Early Life Stages of Freshwater Mussels.

Microplastics have been found in freshwater systems, and in turn have been detected in freshwater bivalves. However, there is limited research that defines the toxicity of bicroplastics to native freshwater bivalves that have long been imperiled in North America. Our objective was to determine whether a suite of pristine microplastics has an adverse effect on two early life stages of unionid freshwater mussels. Glochidia of Lampsilis fasciola (a Canadian species at risk) and Lampsilis siliquoidea (widespread across Canada) were individually exposed to spheres of polystyrene (6 and 90 μm), polyethylene (28, 90, and 1000 μm), and cellulose acetate (1000 μm), as well as fibers of polyethylene terephthalate (60 μm). After 24 h, there was no significant decrease in glochidia viability in either species. Juvenile L. siliquoidea mussels were also exposed to spheres of polystyrene (6 and 90 μm) and polyethylene (28 μm), and fibers of polyethylene terephthalate (60 μm) in individual 28-day subchronic tests followed by a 7-day depuration period. Burial was assessed weekly, and ingestion of each microplastic was compared in nondepurated and depurated mussels. There was no sustained effect on juvenile burial with any microplastic tested. Ingestion of microplastics was concentration dependent, and depuration occurred for all particles and size ranges tested. The results suggest that pristine microplastics were not acutely toxic to the early life stages of these freshwater mussels, but that the energetic costs associated with particle uptake and depuration, which were not measured in our study, may have an impact on fitness that warrants further investigation. In addition, testing with other shapes and polymers of microplastics typically detected in the environment is recommended. Environ Toxicol Chem 2024;00:1-12. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Climate-driven shifts in freshwater biodiversity will impact mitigation costs for hydropower

Climate change is forecasted to drastically alter freshwater fish and mussel species distribution. Hydropower dam reservoirs, which modify downstream thermal regimes, may interact with climate change's impact on species distribution. This distribution shift may feedback, affecting hydropower operation costs through environmental compliance. We investigated how freshwater species distribution will shift due to climate change and hydropower reservoirs in the conterminous United States (CONUS), and how this will affect biodiversity mitigation costs for privately-owned hydropower plants. In general, using environmental niche modeling, we found that climate change increased the range of both freshwater fish and mussel species on average. For fish, this was mainly due to the expanded habitat for warm-water and cool-water fish species despite the diminish in habitat for cold-water species. Compared to climate change, thermal stratification of hydropower reservoirs had a small impact on the future range changes of these species in the tailwaters but showed an interaction with the effect of climate change on species range. Geographically, we projected an increase of species richness in the west and a decrease in the central and east of CONUS for fish, while projecting uniform increase for mussels. With this shift in species distribution, we estimated that the Northwest region will face the largest increase in mitigation cost, while the majority of plants in the Southeast will experience a decrease in cost.

Surviving global change: a review of the impacts of drought and dewatering on freshwater mussels.

The increase in the frequency and intensity of droughts and heatwaves caused by climate change poses a major threat to biodiversity. In aquatic systems, sedentary species such as freshwater mussels are generally considered more vulnerable to changes in habitat conditions than mobile species such as fish. As mussels provide important ecosystem services, understanding the impacts of drought on freshwater mussels is of particular importance for the management of overall functioning of aquatic ecosystems. We used a comprehensive literature search to provide a systematic overview of direct and indirect effects of drought on freshwater mussels (Bivalvia: Unionida) and an evaluation of mitigation strategies. We found that drought studies were concentrated mostly in the USA, with a focus on the Unionidae family. Topics ranged from the physiological effects of high temperatures, emersion, and hypoxia/anoxia to behavioural and reproductive consequences of drought and the implications for biotic interactions and ecosystem services. Studies spanned all levels of biological organization, from individual responses to population- and community-level impacts and ecosystem-wide effects. We identified several knowledge gaps, including a paucity of trait-based evaluation of drought consequences, limited understanding of thermal and desiccation tolerance at the species level, and the synergistic effects of multiple drought stressors on mussels. Although we found many studies provided suggestions concerning management of populations, habitat conditions, and anthropogenic water use, a systematic approach and testing of recommended mitigation strategies is largely lacking, creating challenges for managers aiming to conserve freshwater mussel communities and populations in light of climate change.

Reciprocal transplant experiments demonstrate a dynamic coevolutionary relationship between parasitic mussel larvae and bitterling fishes

Abstract The coevolutionary dynamic of host–parasite associations varies from strictly local adaptations to diffuse guild coevolution. How innate and acquired immune responses modulate host resistance to parasitism and how host specificity and geographic scaling affect the efficacy of host response have consequences for range dynamics and biological invasions. Using reciprocal transplant experiments, we tested whether local or diffuse coevolution shapes host response to parasitism in the host–parasite association between bitterling fishes and larval stages (glochidia) of freshwater mussels from Europe and East Asia. We found that glochidia initially indiscriminately attached to all study host species, but immune responses elicited significant differences in host responses within 24 h of infection, which intensified during glochidial development. European bitterlings were more resistant to European glochidia and Asian bitterlings to Asian glochidia, with the strongest geographic bias in resistance in the Asian bitterling hosts. This finding suggests a strong effect of local adaptation but also indicates the non‐negligible role of coevolutionary hotspots. Low natural glochidia load on bitterling species overall hence arise from competent immune response rather than glochidia avoidance behaviour. Bitterling immune response is primarily innate and not acquired. Overall, our data demonstrate the complex outcome of parasite pressure on the evolution of host resistance, and important role of geographically structured coevolution in shaping host response.

Microeukaryotes Associated with Freshwater Mussels in Rivers of the Southeastern United States.

Microeukaryotes are a diverse and often overlooked group of microbes that are important in food webs and other ecological linkages. Little is known about microeukaryotes associated with aquatic invertebrates, although filter feeders such as mussels are likely to take in and potentially retain microeukaryotes in their gut while feeding. Microeukaryotes such as apicomplexans have been reported in marine mussel species, but no studies have examined the presence of these microorganisms in freshwater mussels or how they relate to mussel host species or environmental conditions. In this study, microbial community DNA was extracted from the gut tissue of over 300 freshwater mussels, representing 22 species collected from rivers in the southeastern USA. Microeukaryote DNA was detected using PCR amplification, followed by the sequencing of positive amplicons. Microeukaryotes were found in 167 individual mussels (53%) of those tested. Amplicons included dinoflagellates/algae that differed between mussel species and are likely food sources that were distinct from those found in water and sediment samples analyzed concurrently. A total of 5% of the positive amplicons were non-photosynthetic alveolates that could represent parasitic microeukaryotes. Understanding the distribution of microeukaryotes in the freshwater mussel gut microbiome could further our understanding of the ongoing decline of mussel populations.

Enhanced Growth Potential of Tilapia (Oreochromis niloticus) Through Maggot-Based Feeding in Multi-Trophic Systems

Highly nutritious insects, such as black soldier fly (BSF) larvae, also referred toas maggot, have been evaluated as feed in monoculture systems, but their use in multi-trophic systems has not been previously investigated. This study used maggot-based feed in a multi-trophic system on a laboratory scale to evaluate the survival and growth performance of tilapia (Oreochromis niloticus). Tilapia were cocultured with freshwater lobster, freshwater clams, and paddy. Four experimental diets were used including a commercial pellet as a control (CP), live maggots (LM), dried maggots (DM), and supplemented maggots (SM). Tilapia (initial weight, 4.1 ± 0.2 g) and other organisms were reared in plastic tanks (water volume 50 L) and randomly distributed into 12 tanks, each containing 20 individual tilapia. The experimental diets were given four times a day at a feeding rate of 10% tilapia biomass. After 28 days of feeding, the survival and growth of tilapia on the CP diet were 90.0% and 2.8% day-1, LM 93.3% and 2.7% day-1, DM 93.3% and 3.3% day-1, and SM 90.0% and 3.1% day-1, respectively. There was no significant effect (P > 0.05) on the survival performance among the experimental diets. However, the growth confirmed by Specific Growth Rate (SGR) showed a significant effect (P < 0.05). SGR values were found to be significantly higher in the DM and SM diets than in the CP diet. An important finding of this research is the potential of maggot-based feed to increase the growth of tilapia in multi-trophic systems without impairing their survival.

Assessment of haemolymph parameters of some freshwater snails and mussels collected from a lentic habitat of Bangladesh

ABSTRACT The present study was conducted to determine certain haemolymph parameters of natural populations of two freshwater snails Pila globosa and Filopaludina bengalensis, and four unionid mussels Lamellidens jenkinsianus, L. phenchooganjensis, L. marginalis, and L. corrianus collected from Darikanthal Beel, Trishal, Mymensingh. Twenty apparently healthy live snails and mussels from each population collected at the same date were selected for haemolymph analysis. A non-lethal sampling technique was adopted for collecting haemolymph from the snails and mussels. The haemolymph parameters Na+, K+, Cl−, glucose concentrations and pH levels were determined for each specimen. Significant differences (P < 0.05) were found in almost all the haemolymph parameters among the sampled snail and mussel populations. This study provided reference ranges for some vital haemolymph parameters of the two freshwater snail species and four unionid mussel species. These ranges are measurable non-lethally and could be applied to biological monitoring of environmental stressors using the molluscs as indicator species.

Identification and antibacterial activity of a novel phage-type lysozyme from the freshwater mussel Hyriopsis cumingii

A cDNA encoding a phage-type lysozyme, designated as HcPLYZ, was successfully cloned from Hyriopsis cumingii. The full-length cDNA sequence of HcPLYZ was determined to be 896 base pairs in length. Analysis revealed the absence of a signal peptide at its N-terminus, and identified two highly conserved phage-type lysozyme activity sites, Glu20 and Asp29, within the deduced amino acid sequence of HcPLYZ. The results of the cloning and sequencing symbiotic bacteria in tissues were consistent with those obtained using tissue cDNA as the template, suggesting that HcPLYZ may originate a symbiotic bacterium. The expression levels of HcPLYZ mRNA exhibited significant variations across different tissues. Successful expression was induced using IPTG, and the native recombinant protein was subsequently purified through affinity chromatography employing Ni2+, and the optimal pH and temperature of which were determined to be 5.5 and 50°C, respectively. Following exposure to Aeromonas hydrophila, there was a significant increase in the levels of HcPLYZ mRNA in the hemocytes, hepatopancreas, and gills. HcPLYZ was demonstrated the inhibition activity of 55% and 83% against Micrococcus lysodeikticus under pH 5.5 and 50 °C conditions, respectively. These results suggested that HcPLYZ possessed antibacterial activity against both A. hydrophila and M. lysodeikticus.

Freshwater Mussel Viromes Increase Rapidly in Diversity and Abundance When Hosts Are Released from Captivity into the Wild.

Freshwater mussels (order: Unionida) are highly imperiled globally and are increasingly the focus of captive propagation efforts to protect and restore wild populations. The Upper Tennessee River Basin (UTRB) in Virginia is a freshwater biodiversity hotspot hosting at least 45 of North America's ~300 species of freshwater mussels, including 21 threatened and endangered species listed under the U.S. Endangered Species Act. Recent studies have documented that viruses and other microbes have contributed to freshwater mussel population declines in the UTRB. We conducted a multi-year longitudinal study of captive-reared hatchery mussels released to restoration sites throughout the UTRB to evaluate their viromes and compare them to captive hatchery environments. We documented 681 viruses from 27 families. The hatchery mussels had significantly less viruses than those deployed to wild sites, with only 20 viruses unique to the hatchery mussels. After the hatchery mussels were released into the wild, their number of viruses initially spiked and then increased steadily over time, with 451 viruses in total unique to the mussels in the wild. We found Clinch densovirus 1 (CDNV-1), a virus previously associated with mass mortality events in the Clinch River, in all samples, but the wild site mussels consistently had significantly higher CDNV-1 levels than those held in the hatchery. Our data document substantial differences between the viruses in the mussels in the hatchery and wild environments and rapid virome shifts after the mussels are released to the wild sites. These findings indicate that mussel release programs might benefit from acclimatization periods or other measures to mitigate the potential negative effects of rapid exposure to infectious agents found in natural environments.

Controls on the Barium and Strontium Isotopic Records of Water Chemistry Preserved in Freshwater Bivalve Shells.

Biogenic carbonates, including bivalve shells, record past environmental conditions, but their interpretation requires understanding environmental and biological factors that affect trace metal uptake. We examined stable barium (δ138Ba) and radiogenic strontium (87Sr/86Sr) isotope ratios in the aragonite shells of four native freshwater mussel species and two invasive species in five streams and assessed the effects of species identity, growth rate, and river water chemistry on shell isotopic composition. Shells were robust proxies for Sr, accurately reflecting 87Sr/86Sr ratios of river water, regardless of species or growth rate. In contrast, shell δ138Ba values, apart from invasive Corbicula fluminea, departed widely from those of river water and varied according to species and growth rate. Apparent fractionation between river water and the shell (Δ138Bashell-water) reached -0.86‰, the greatest offset observed for carbonate minerals. The shell deposited during slow growth periods was more enriched in lighter Ba isotopes than the rapidly deposited shell; thus, this phenomenon cannot be explained by aragonite precipitation kinetics. Instead, biological ion transport processes linked to growth rate may be largely responsible for Ba isotope variation. Our results provide information necessary to interpret water chemistry records preserved in shells and provide insights into biomineralization processes and bivalve biochemistry.

Description of a new freshwater mussel species of Pletholophus, Simpson, 1900 (Bivalvia, Unionidae) from Guangdong, China

The Pearl River Basin, China’s second-largest freshwater basin, hosts a significant diversity of species and a highly endemic freshwater mussel fauna. In this study, a new species from the Liuxi River in Guangzhou, Guangdong, China, Pletholophus guangzhouensissp. nov., is described based on morphological diagnostic features and molecular phylogenetics. The glochidia shells of the new species are subtriangular, medium-sized, and have a styliform hook on the ventral angle of each valve. Phylogenetic analyses based on the COI and 28S rRNA gene fragments indicated that Pletholophus guangzhouensissp. nov. is the sister to Pletholophus tenuis + Pletholophus reinianus. The pairwise uncorrected COI p-distance analysis demonstrated genetic distances ranging from 5.27% (between P. guangzhouensissp. nov. and P. tenuis) to 11.06% (between P. guangzhouensissp. nov. and P. honglinhensis). Our findings suggest a significant underestimation of the diversity of freshwater mussel species in Guangdong. Further field collections and systematic studies are necessary to fully explore the biodiversity of this region. Furthermore, integrative classification methods and genetic research are essential for informing the development of effective conservation strategies.

Multisystemic inflammatory disease in Pheasantshell (Unionidae, Actinonaias pectorosa) associated with Yokenella regensburgei infection at sites experiencing seasonal mass mortality events.

Freshwater mussels are integral components of riverine ecosystems, influencing water quality, nutrient cycling, and habitat characteristics. Enigmatic freshwater mussel declines, often characterized by sudden mass mortality events, pose significant challenges to conservation efforts. The Clinch River, a freshwater biodiversity hotspot in Virginia and Tennessee, USA, has experienced several enigmatic mass mortality events since 2016. Studies have reported bacteria associated with moribund Pheasantshell (Actinonaias pectorosa) during mortality events in the Clinch River, specifically Yokenella regensburgei. Despite reports of bacterial infection, little is known about their role as pathogens. Through a multiyear case-control study, combining in-situ experiments, field surveys, histology, bacterial isolation, and high-throughput sequencing, we assessed the role of bacteria in Pheasantshell (Actinonais pectorosa) mortality at three sites in the Clinch River. Between May 2021 and December 2023, we collected 21 wild moribund free-living A. pectorosa and 68 hatchery-reared A. pectorosa maintained in silos at the same sites and investigated differences in pathology and microbiologye between groups. No silo mussels presented clinical signs of disease, or gross or microscopic lesions associated with pathological conditions leading to mortality. Our findings reveal a significant association between Yokenella regensburgei and severe multisystemic and multifocal infiltrative hemocytosis with necrosis, consistent with sepsis. Lesions associated with yokenellosis were of sufficient severity and physiological significance to explain mortality in infected hosts. Although our study does not explain the cause of these infections, it confirms that mussels at our study sites are ultimately dying with an infectious disease and that Y. regensburgei can be pathogenic in free-living mussels. Our results underscore the importance of considering bacterial diseases in wild mussel populations and emphasize the need for further research to elucidate the epidemiology and pathogenicity of Y. regensburgei. Overall, our study highlights the importance of integrated approaches combining pathology, microbiology, and epidemiology in freshwater mussel conservation efforts.

The potential compensatory mechanism between pmbA and tldD governing the virulence of Aeromonas veronii and its implications on the immune response in freshwater bivalve (Hyriopsis cumingii)

Aeromonas veronii is an opportunistic pathogen that causes diseases in aquatic animals, but its key virulence factors remain unclear. In order to evaluate the feasibility of potential compensatory mechanism to be a novel target for developing live attenuated vaccine, virulence-related phenotypes and the immune response of H. cumingii were measured. Then two single-deletion mutants ΔPmbA, ΔTldD and one double-deletion mutant ΔP&T were constructed by homologous recombination. The hemolytic activity of double-deletion mutant ΔP&T showed dramatically lower than wide-type GL2 (P < 0.05), and the two genes could significantly regulate the proteolytic activity on skimmed milk (P < 0.05), except for casein (P > 0.05). All mutants exhibited attenuated capacities to form biofilms (P < 0.05), and pmbA mRNA was upregulated dramatically (P < 0.05) under exogenous threats modeled by osmotic stress, in which tldD mRNA was overlapped. Besides, the absence of one gene resulted in significantly higher (P < 0.05) mRNA level of another gene. ftsH mRNA was restrained dramatically (P < 0.05) in all mutants, and aerA mRNA was suppressed remarkably (P < 0.05) in ΔP&T. Challenge tests showed that the pathogenicity of ΔP&T on Hyriopsis cumingii was further reduced compared with the two single-deletion mutants, and its LD50 was 6.31-fold than that of GL2. In addition, enzymatic activities in the hemolymph and hepatopancreas of ΔP&T group were significantly lower (P < 0.05) than those in GL2 group at different time points, and their peaks in hepatopancreas were found almost at 12 h post challenge, which were supported by the qPCR results of HcIL-17 and TR. Besides, histopathological examination displayed that the degree of tissue damage in ΔP&T group was alleviated remarkably compared with GL2 group. Finally, bacterial loads in the hemolymph and hepatopancreas of ΔP&T group were lower significantly (P < 0.05) than other groups. The above results demonstrate that the compensatory mechanism between the genes pmbA and tldD is a novel target to attenuate A. veronii, and the double-deletion mutant ΔP&T is helpful for the development of live attenuated vaccine.

Reproductive Strategies and Embryonic Development of Autumn-Spawning Bitterling (Acheilognathus rhombeus) within the Mussel Host.

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.

The reproductive costs of bitterling fish and zebra mussel parasitism to a unionid mussel

Unionid mussels are one of the most vulnerable groups of animals, with multitude of factors responsible for the decline of their populations in the freshwater ecosystems. Many of those causes stem from interspecific relationships. Direct data on the reproductive costs incurred to unionids through parasitism by fish and other mussel species are incomplete. We used field experiments to test whether reproduction of the swollen river mussel (Unio tumidus) is affected by parasitism by the European bitterling fish (Rhodeus amarus) and zebra mussel (Dreissena polymorpha). We documented that bitterling brood can develop in the gills of female, male and hermaphrodite mussels. Our research showed that male mussels carried more fish offspring than female U. tumidus and bitterling embryo survival appeared higher in the outer gill demibranchs. Parasitised female U. tumidus suffered reduced fecundity in terms of a reduced number of mature ovulated oocytes and increased oocyte degeneration. Our data lend clear support to the hypothesis that bitterling fish embryos parasitizing mussel gills and epibiont zebra mussel fouling unionid shells represent a major cost to the reproductive success of their host mussels. Extended gonadal activity (multiple spawning) of U. tumidus spreads their spawning time over a longer period, which may mitigate the costs of parasitism.

Assessment of the viral contamination of fecal origin over a wide geographical area using an active approach with Dreissena polymorpha

Biomonitoring appears to be a key approach to assess chemical or microbiological contaminations. The freshwater mussel, Dreissena polymorpha (D. polymorpha), is a suitable tool already used to monitor chemical and, more recently, microbiological pollution. In the present study, we used this sentinel species to monitor viral contamination of fecal origin over a wide geographical distribution. An active approach was implemented based on caging of calibrated and pathogen-free organisms with the same exposure conditions, allowing spatio-temporal comparisons between different water bodies. In addition, different types of sites were selected to investigate the range of environmental concentrations that D. polymorpha are able to translate. Different viral genome targets were measured: norovirus genogroup I and II (NoV GI and GII) and F-specific RNA bacteriophages belonging to the genogroup –I and –II (FRNAPH-I and -II). Total infectious FRNAPH were also monitored.D. polymorpha was able to translate a wide range of concentrations for all the viral targets studied, meaning that this sentinel species can be used for both low and highly anthropised sites. Moreover, D. polymorpha caging proved effective in achieving gradients of viral contamination of fecal origin pressure and to highlight the contribution of tributaries to the main rivers. D. polymorpha provided spatial and temporal variations of the viral contamination. It allowed to highlight the prevalence of the FRNAPH-I and -II genogroups according to the caging site. FRNAPH-II was found to be dominant in urban areas and FRNAPH-I in rural areas. This strategy uses the caging of the sentinel species D. polymorpha on selected sites with standardised analysis methods has proven to be a promising tool for characterizing viral contamination at both large and very fine scales.

Off the conservation radar: the hidden story of Europe's tiny pea clams (Bivalvia: Sphaeriidae)

AbstractThis study highlights the conservation problems faced by the tiny freshwater bivalves of the family Sphaeriidae, also known as pea, pill, or fingernail clams (or mussels) in Europe. Despite their global distribution, assumed ecological importance, and potential uses, basic knowledge about their taxonomy, biology, and ecology is very limited and much lower than for the larger freshwater bivalve taxa. Immediate scientific priorities are required to fill knowledge gaps regarding their taxonomy, genetic diversity, distribution, reproductive cycle, ecosystem functions, and population trends. Such fundamental knowledge is necessary to identify specific threats and develop appropriate conservation actions. Deploying environmental DNA analysis at a large scale could be a valuable way to fill gaps in distribution and strengthen monitoring in areas where local taxonomic knowledge is lacking. Until taxon-specific management plans can be developed, we recommend that efforts concentrate on the general protection and restoration of wetland habitats, implementing pollution control measures, and managing invasive species. These actions should be complemented by community engagement through citizen science initiatives. Additionally, prioritising data collection to fill existing knowledge gaps and updating conservation statuses (Red Lists) based on comprehensive assessments will be crucial. Implementing these actions will provide a starting point for the broader protection of freshwater ecosystems, thus benefiting pea clams and other interconnected species within these habitats.

Still waters and deep: Habitat characteristics, density and distribution of a lake-dwelling population of the freshwater pearl mussel Margaritifera margaritifera

The freshwater pearl mussel, Margaritifera margaritifera is widely considered to be confined to fast-flowing, near-pristine rivers, and is highly endangered throughout its Holartic range. Here we describe a large population of some 150–200,000 individuals of the freshwater pearl mussel living in an oligotrophic Irish lake.Employing underwater photographic techniques and snorkel diving, mussels were found in two separate locations in the lake. In the first location, 200 m from the shore, mussels were found at a maximum density of 43 m−2, in a largely random distribution in the sandy bed substrate of the lake, up to 9.5 m deep. In the second shoreline location, mussels were observed in dense aggregations up to 118 individuals m−2, in sandy pockets in between boulders and bedrock, in waters 1–2 m deep. In both locations, mussels were found associated with macrophytes – the charophyte Nitella sp. in the deeper location and the quillwort Isoetes lacustris in the shallower shoreline location. Juvenile mussels (>1.5 cm length) were observed lying exposed on the sediment surface in the shallow littoral location, indicating that recruitment occurs in this population, although no estimates of juvenile density were obtained.The discovery of a large population of lentic Margaritifera margaritifera has significant implications for the species’ conservation and indicates that there may be substantial lentic populations of the species elsewhere. The environmental envelope of the species is clearly much wider than thought and our discovery challenges assumptions about the fundamental feeding and reproductive biology of this endangered species.