Seasonal Monitoring of Heavy Metal Pollution in Water and Zebra Mussels Dreissena polymorpha as a Potential Bioindicator Species from Lake Habitat.

In aquatic ecosystem, metal pollution is an important environmental hazard. Mussels as a bioindicator species are often used for assessment the presence of potentially toxic metals. Hence, the present study aimed to assess the effect of seasonal variations on some heavy metals (Cd, Cr, Pb, As, Zn and Cu) accumulation in water and Dreissena polymorpha from lake habitat. Our result indicated that Zn accumulated at a very high level in the zebra mussels while As accumulated at a high level in water samples. Seasonal variations significantly affected Cu concentration in the water samples (P < 0.05) while Cr concentration in the mussel samples was significantly affected by seasonal variations (P < 0.05). According to the water analysis, mean concentrations of metals are below the maximum limits established by the World Health Organization and USEPA, except As. Overall, our data emphasize anthropogenic pollution in the Turkish aquatic environment and confirm the use of D. polymorpha as a prospective biomonitor for metal polluted sites'.

Aquatic macroinvertebrate community responses to pollution of perfluoroalkyl substances (PFAS): Can we define threshold body burdens?

The pollution of per- and polyfluorinated alkyl substances (PFAS) in aquatic environments is a worldwide concern of which the ecological impact is still not well understood. Especially field-based effect studies in aquatic ecosystems are generally lacking, creating a knowledge gap that goes along with monitoring and regulatory challenges. Therefore, this study examined if bioaccumulated PFAS concentrations could be related to ecological responses assessed by changes in the macroinvertebrate community structure. In addition, threshold body burdens that are protective of ecological damage were estimated. Aquatic macroinvertebrates were sampled in 30 streams across Flanders (Belgium) and 28 PFAS target analytes were measured in three resident taxa (Gammarus sp., Asellus sp. and Chironomus sp.) and translocated zebra mussels (Dreissena polymorpha). The macroinvertebrate community structure was assessed by calculating the Multimetric Macroinvertebrate Index Flanders (MMIF). Primarily long-chain perfluorinated carboxylic acids (PFCAs) were detected in both resident taxa (passive biomonitoring) and zebra mussels (active biomonitoring). Based on a 90th quantile regression model, safe threshold body burdens could be calculated for PFTeDA (7.1 ng/g ww) and ΣPFAS (2264 ng/g ww) in Gammarus sp. and for PFOA (5.5 ng/g ww), PFDoDA (1.7 ng/g ww), PFTrDA (0.51 ng/g ww), PFTeDA (2.4 ng/g ww), PFOS (644 ng/g ww) and ΣPFAS (133 ng/g ww) in zebra mussel. An additional threshold value was calculated for most compounds and species using the 95th percentile method. However, although these estimated thresholds are pertinent and indicative, regulatory applicability requires further lines of evidence and validation. Nevertheless, this study offers first-time evidence of associations between accumulated PFAS concentrations in invertebrates and a reduced ecological water quality in terms of macroinvertebrate community structure and highlights the potential of Gammarus sp. and zebra mussels to serve as reliable PFAS biomonitoring species.

Assessing viral freshwater hazard using a toxicokinetic model and Dreissena polymorpha.

The detection all pathogenic enteric viruses in water is expensive, time-consuming, and limited by numerous technical difficulties. Consequently, using reliable indicators such as F-specific RNA phages (FRNAPH) can be well adapted to assess the risk of viral contamination of fecal origin in surface waters. However, the variability of results inherent to the water matrix makes it difficult to use them routinely and to interpret viral risk. Spatial and temporal variability of surface waters can lead to underestimate this risk, in particular in the case of low loading. The use of bivalve mollusks as accumulating systems appears as a promising alternative, as recently highlighted with the freshwater mussel Dreissena polymorpha, but its capacity to accumulate and depurate FRNAPH needs to be better understood and described. The purpose of this study is to characterise the kinetics of accumulation and elimination of infectious FRNAPH by D. polymorpha in laboratory conditions, formalised by a toxico-kinetic (TK) mechanistic model. Accumulation and depuration experiments were performed at a laboratory scale to determine the relationship between the concentration of infectious FRNAPH in water and the concentration accumulated by D. polymorpha. The mussels accumulated infectious FRNAPH (3-5.4 × 104 PFU/g) in a fast and concentration-dependent way in only 48 h, as already recently demonstrated. The second exposure demonstrated that the kinetics of infectious FRNAPH depuration by D. polymorpha was independent to the exposure dose, with a T90 (time required to depurate 90 % of the accumulated concentration) of approximately 6 days. These results highlight the capacities of D. polymorpha to detect and reflect the viral pollution in an integrative way and over time, which is not possible with point water sampling. Different TK models were fitted based on the concentrations measured in the digestive tissues (DT) of D. polymorpha. The model has been developed to formalise the kinetics of phage accumulation in mussels tissues through the simultaneous estimation of accumulation and depuration rates. This model showed that accumulation depended on the exposure concentration, while depuration did not. Standardized D. polymorpha could be easily transplanted to the environment to predict viral concentrations using the TK model defined in the present study to predict the level of contamination of bodies of water on the basis of the level of phages accumulated by the organisms. It will be also provide a better understanding of the dynamics of the virus in continental waters at different time and spatial scales, and thereby contribute to the protection of freshwater resources.

Biochemical basis of resistance to multiple contaminations in the native and invasive populations of Dreissena polymorpha.

The zebra mussel Dreissena polymorpha (Pallas, 1771) is an invasive species and a valuable bioindicator in the inland waters. Nevertheless, the biochemical reasons for the unique competitiveness of zebra mussels are not clear. This study aimed to compare the native and invasive populations of D. polymorpha in their ability to withstand the same multiple environmental challenges (i.e. chemical: microplastics and caffeine; physical: temperatures). The specimens from the invasive population in west Ukraine (Tn) and native population at lower streams of river Dnipro (south Ukraine, Kh) were sampled in the August of 2021 y. Molluscs from both populations were treated simultaneously with microplastics (MP, 1 mg L-1, pore size 2 µm); caffeine (Caf, 20.0 µg L-1) at 18 °C, elevated temperature (25 °C) and MP and Caf combinations at 18 °C and 25 °C for 14 days. Untreated molluscs exposed at 18 °C represented control groups. A set of the 20 markers of oxidative stress, biotransformation, detoxification and apoptosis were assayed in the total soft tissues. From the two controls, Kh-group indicated lower stressful impact. However, both populations increased caspase-3 and GST activities and lysosomal instability in most exposures, and cholinesterase and phenoloxidase activities under the heating and combine exposures, indicating the remarkable properties to respond to new challenges and synergistic effect of mixtures. Inter-population differences were related to the metallothionein, cathepsin D, cytochrome P540 and oxidative stress responses that reflect population-dependent adverse outcome pathways. The discriminant analysis separated two populations with a substantially lesser magnitude of responses in the invasive population as a sign of higher resistance.

Contaminants of Concern and Spatiotemporal Metabolomic Changes in Quagga Mussels (Dreissena bugensis rostriformis) from the Milwaukee Estuary (Wisconsin, USA).

Environmental metabolomics has emerged as a promising technique in the field of biomonitoring and as an indicator of aquatic ecosystem health. In the Milwaukee Estuary (Wisconsin, USA), previous studies have used a nontargeted metabolomic approach to distinguish between zebra mussels (Dreissena polymorpha) collected from sites of varying contamination. To further elucidate the potential effects of contaminants on bivalve health in the Milwaukee Estuary, the present study adopted a caging approach to study the metabolome of quagga mussels (Dreissena bugensis rostriformis) deployed in six sites of varying contamination for 2, 5, or 55 days. Caged mussels were co-deployed with two types of passive sampler (polar organic chemical integrative samplers and semipermeable membrane devices) and data loggers. In conjunction, in situ quagga mussels were collected from the four sites studied previously and analyzed for residues of contaminants and metabolomics using a targeted approach. For the caging study, temporal differences in the metabolomic response were observed with few significant changes observed after 2 and 5 days, but larger differences (up to 97 significantly different metabolites) to the metabolome in all sites after 55 days. A suite of metabolic pathways were altered, including biosynthesis and metabolism of amino acids, and upmodulation of phospholipids at all sites, suggesting a potential biological influence such as gametogenesis. In the caging study, average temperatures appeared to have a greater effect on the metabolome than contaminants, despite a large concentration gradient in polycyclic aromatic hydrocarbons residues measured in passive samplers and mussel tissue. Conversely, significant differences between the metabolome of mussels collected in situ from all three contaminated sites and the offshore reference site were observed. Overall, these findings highlight the importance of contextualizing the effects of environmental conditions and reproductive processes on the metabolome of model organisms to facilitate the wider use of this technique for biomonitoring and environmental health assessments. Environ Toxicol Chem 2024;43:307-323. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Invasive mussels fashion silk-like byssus via mechanical processing of massive horizontally acquired coiled coils.

Zebra and quagga mussels (Dreissena spp.) are invasive freshwater biofoulers that perpetrate devastating economic and ecological impact. Their success depends on their ability to anchor onto substrates with protein-based fibers known as byssal threads. Yet, compared to other mussel lineages, little is understood about the proteins comprising their fibers or their evolutionary history. Here, we investigated the hierarchical protein structure of Dreissenid byssal threads and the process by which they are fabricated. Unique among bivalves, we found that threads possess a predominantly ß-sheet crystalline structure reminiscent of spider silk. Further analysis revealed unexpectedly that the Dreissenid thread protein precursors are mechanoresponsive α-helical proteins that are mechanically processed into ß-crystallites during thread formation. Proteomic analysis of the byssus secretory organ and byssus fibers revealed a family of ultrahigh molecular weight (354 to 467 kDa) asparagine-rich (19 to 20%) protein precursors predicted to form α-helical coiled coils. Moreover, several independent lines of evidence indicate that the ancestral predecessor of these proteins was likely acquired via horizontal gene transfer. This chance evolutionary event that transpired at least 12 Mya has endowed Dreissenids with a distinctive and effective fiber formation mechanism, contributing significantly to their success as invasive species and possibly, inspiring new materials design.

Factors determining bioaccumulation of neurotoxicant Hg in the zebra mussels (Dreissena polymorpha): Influence of biometric parameters, sex and storage of shell.

One of benthic organisms exposed to contact with mercury in the southern Baltic is alien species of clam: Dreissena polymorpha. As this organism is increasingly dynamic in various regions of the world including the southern Baltic region, it is reasonable to ask whether it tolerates elevated concentrations of xenobiotics? Does it effectively eliminate Hg? The study determined the effects of biometric parameters and water temperature on the rate of accumulation and efficiency of eliminating Hg from body. Investigations focused on the shell which represents poorly-recognized role in the process of Hg distribution in clams. The results showed that especially during warm season, clams effectively reduced the levels of Hg in their body by the biodilution of Hg and reproduction. Important factor influencing detoxification was Hg transfer from the soft tissue to the shell. This protects the soft tissue against the toxic effect of Hg.

Tipping point arises earlier under a multiple-stressor scenario.

Anthropogenic impacts and global changes have profound implications for natural ecosystems and may lead to their modification, degradation or collapse. Increases in the intensity of single stressors may create abrupt shifts in biotic responses (i.e. thresholds). The effects of multiple interacting stressors may create non-additive responses, known as synergistic or antagonistic interactions. Here we combine both concepts-ecological thresholds and interactions between multiple stressors-to understand the effects of multiple interacting stressors along environmental gradients, and how this can affect the occurrence of thresholds. Using an experimental approach to investigate the effect of nutrient enrichment and saltwater intrusion on mortality in the zebra mussel, Dreissena polymorpha, we show that multiple stressors can create thresholds at lower levels of an environmental gradient. Our results reveal a major shortcoming in how we currently investigate these two ecological concepts, as considering them separately may be causing underestimation of thresholds and stressor-interaction impacts.

First Confirmed Case of Canine Mortality Due to Dihydroanatoxin-a in Central Texas, USA.

The frequency of dogs becoming ill or dying from accidental exposure to cyanotoxins, produced by cyanobacteria, is increasing throughout the United States. In January and February of 2021, two dogs died and five dogs became ill after swimming in Lake Travis, central Texas, USA; one deceased dog (C1) was subjected to pathological testing. Algal materials, sediment samples, zebra mussel viscera, periphyton from shells, as well as fluids and tissues from the digestive tract of C1 were investigated for the following cyanotoxins: anatoxin-a, homoanatoxin-a, dihydroanatoxin-a (dhATX), cylindrospermopsin, saxitoxin, and microcystins. Necropsy results of C1 indicated neurotoxicosis with significant levels of dhATX in the duodenum tissues (10.51 ng/g dry weight (DW)), jejunum tissue (6.076 ng/g DW), and stomach contents (974.88 ng/g DW). Algae collected near the site of C1's death contained levels of dhATX, ranging from 13 to 33 µg/g. By comparison, dhATX was detected at much lower concentrations in sediment samples (310.23 ng/g DW) and the periphyton on zebra mussel shells (38.45 ng/g DW). While dhATX was suspected in the deaths of canines from an event in Texas in 2019, this is the first report linking dhATX neurotoxicosis through pathological findings in Texas and potentially in the United States.

Bioaccumulation and molecular effects of carbamazepine and methylmercury co-exposure in males of Dreissena polymorpha.

Dreissena polymorpha is a bivalve promising for biomonitoring in freshwater ecosystems thanks to its abundance and high filtration activity allowing rapid uptake of toxicants and identification of their negative effects. Nonetheless, we still lack knowledge on its molecular responses to stress under realistic scenario, e.g. multi-contamination. Carbamazepine (CBZ) and Hg are ubiquitous pollutants sharing molecular toxicity pathways, e.g. oxidative stress. A previous study in zebra mussels showed their co-exposure to cause more alterations than single exposures, but molecular toxicity pathways remained unidentified. D. polymorpha was exposed 24 h (T24) and 72 h (T72) to CBZ (6.1 ± 0.1 µg L-1), MeHg (430 ± 10 ng L-1) and the co-exposure (6.1 ± 0.1 µg L-1CBZ and 500 ± 10 ng L-1 MeHg) at concentrations representative of polluted areas (~10× EQS). RedOx system at the gene and enzyme level, the proteome and the metabolome were compared. The co-exposure resulted in 108 differential abundant proteins (DAPs), as well as 9 and 10 modulated metabolites at T24 and T72, respectively. The co-exposure specifically modulated DAPs and metabolites involved in neurotransmission, e.g. dopaminergic synapse and GABA. CBZ specifically modulated 46 DAPs involved in calcium signaling pathways and 7 amino acids at T24. MeHg specifically modulated 55 DAPs involved in the cytoskeleton remodeling and hypoxia-induced factor 1 pathway, without altering the metabolome. Single and co-exposures commonly modulated proteins and metabolites involved in energy and amino acid metabolisms, response to stress and development. Concomitantly, lipid peroxidation and antioxidant activities were unchanged, supporting that D. polymorpha tolerated experimental conditions. The co-exposure was confirmed to cause more alterations than single exposures. This was attributed to the combined toxicity of CBZ and MeHg. Altogether, this study underlined the necessity to better characterize molecular toxicity pathways of multi-contamination that are not predictable on responses to single exposures, to better anticipate adverse effects in biota and improve risk assessment.

A comparison of survey method efficiencies for estimating densities of zebra mussels (Dreissena polymorpha).

Abundance surveys are commonly used to estimate plant or animal densities and frequently require estimating detection probabilities to account for imperfect detection. The estimation of detection probabilities requires additional measurements that take time, potentially reducing the efficiency of the survey when applied to high-density populations. We conducted quadrat, removal, and distance surveys of zebra mussels (Dreissena polymorpha) in three central Minnesota lakes and determined how much survey effort would be required to achieve a pre-specified level of precision for each abundance estimator, allowing us to directly compare survey design efficiencies across a range of conditions. We found that the required sampling effort needed to achieve our precision goal depended on both the survey design and population density. At low densities, survey designs that could cover large areas but with lower detection probabilities, such as distance surveys, were more efficient (i.e., required less sampling effort to achieve the same level of precision). However, at high densities, quadrat surveys, which tend to cover less area but with high detection rates, were more efficient. These results demonstrate that the best survey design is likely to be context-specific, requiring some prior knowledge of the underlying population density and the cost/time needed to collect additional information for estimating detection probabilities.

Modulation of haemocyte motility by chemical and biological stresses in Mytilus edulis and Dreissena polymorpha.

Mussels are constantly exposed to various pollutants in the environment, which can impair their immune defences against microbes and thus threaten their survival. In this study, we expand the insight into a key parameter of immune response in two mussel species by exploring the impact of exposure to pollutants or bacteria or simultaneous chemical and biological exposure on haemocyte motility. Basal haemocyte velocity in primary culture was high and increasing over time in Mytilus edulis (mean cell speed of 2.32 µm/min ± 1.57) whereas Dreissena polymorpha showed a constant and rather low cell motility with time (mean cell speed of 0.59 µm/min ± 0.1). In the presence of bacteria, the motility of haemocytes was instantly enhanced and slowed down after 90 min for M. edulis. In contrast, in vitro exposure of haemocytes to chemicals, either Bisphenol A, oestradiol, copper, or caffeine, induced an inhibition of cell motility in both mussel species. Finally, the cellular activation observed during bacterial challenges was inhibited by simultaneous exposure to bacteria and pollutants. Overall, our results indicate that chemical contaminants can alter haemocyte migration in mussels which can weaken their response to pathogens and therefore increase their susceptibility to infectious diseases.

Integrative biomarker response - Threshold (IBR-T): Refinement of IBRv2 to consider the reference and threshold values of biomarkers.

The Integrated Biomarker Response (IBR) is one of the most used index in biomonitoring, especially the IBRv2 integrating a reference condition. However, some limitations remain for its routine and large-scale use. The IBRv2 is proportional to the total number of biomarkers, is dependent on the nature of biomarkers and considers all biomarkers modulations, even small and biologically non-significant. In addition, IBRv2 relies on reference values but the references are often different between each study, making it difficult to compare results between studies and/or campaigns. To overcome these limitations, the present work proposed a new index called IBR-T ("Integrated Biomarker Response - Threshold") which considers the threshold values of biomarkers by limiting the calculation of the IBR value to biomarkers with significant modulations. The IBRv2 and the IBR-T were calculated and compared on four datasets from active biomonitoring campaigns using Dreissena polymorpha, a bivalve widely used in freshwater biomonitoring studies. The comparison between indices has demonstrated that the IBR-T presents a better correlation (0.907 < r2 < 0.998) with the percentage of biomarkers significantly modulated than the IBRv2 (0.002 < r2 < 0.759). The IBRv2 could not be equal to 0 (0.915 < intercept <1.694) because the value was dependent on the total number of biomarkers, whereas the IBR-T reached 0 when no biomarker was significantly modulated, which appears more biologically relevant. The final ranking of sites was different between the two index and the IBR-T ranking tends to be more ecologically relevant that the IBRv2 ranking. This IBR-T have shown an undeniable interest for biomonitoring and could be used by environmental managers to simplify the interpretation of large datasets, directly interpret the contamination status of the site, use it to decision-making, and finally to easily communicate the results of biomonitoring studies to the general public.

Review and Development of Best Practices for Toxicity Tests with Dreissenid Mussels.

Since their introduction to North America in the 1980s, research to develop effective control tools for invasive mussels (Dreissena polymorpha and D. rostriformis bugensis) has been ongoing across various research institutions using a range of testing methods. Inconsistencies in experimental methods and reporting present challenges for comparing data, repeating experiments, and applying results. The Invasive Mussel Collaborative established the Toxicity Testing Work Group (TTWG) in 2019 to identify "best practices" and guide development of a standard framework for dreissenid mussel toxicity testing protocols. We reviewed the literature related to laboratory-based dreissenid mussel toxicity tests and determined the degree to which standard guidelines have been used and their applicability to dreissenid mussel testing. We extracted detailed methodology from 99 studies from the peer-reviewed and gray literature and conducted a separate analysis for studies using presettlement and postsettlement mussels. We identified specific components of methods and approaches that could be refined or standardized for dreissenid mussels. These components included species identification, collection methods, size/age class distinction, maintenance practices, testing criteria, sample size, response measures, reporting parameters, exposure methods, and mortality criteria. We consulted experts in the field of aquatic toxicology and dreissenid mussel biology on our proposed. The final recommendations contained in the present review are based on published standard guidelines, methods reported in the published and gray literature, and the expertise of TTWG members and an external panel. In addition, our review identifies research needs for dreissenid mussel testing including improved methods for early-life stage testing, comparative data on life stages and between dreissenid mussel species, inclusion of a reference toxicant, and additional testing of nontarget species (i.e., other aquatic organisms). Environ Toxicol Chem 2023;42:1649-1666. © 2023 His Majesty the King in Right of Canada. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Dreissena polymorpha responses under thermal and hypoxic stress: New insights in the tolerance of this freshwater sentinel species.

Dreissena polymorpha is a sentinel freshwater mussel providing key functional ecosystemic services like nutrient recycling and suspended matter filtration. Global warming and especially extreme events imply rapid fluctuations of environmental parameters that sessile organisms could not escape. The increase occurrence of heat waves and the subsequent expansion of hypoxic areas could challenge the survival of mussels. This study provided a deeper knowledge of energy management and cellular function during thermal (+15 °C) or hypoxic (30% of dissolved oxygen saturation) stress for 7 days. A potential metabolic rate depression was highlighted in D. polymorpha under hypoxia through a decline in the mitochondrial activity and a constant AMP content over time. A contrasted pattern of response was observed in thermal-stressed mussels between 24 h and 7 days of exposure. A global increase of metabolic activity was noticed in mussels after 24 h while a return to control level was noticed at the end of the experiment. Although D. polymorpha is considered as a temperature tolerant species, a significant increase of ADP:ATP ratio, related to a decrease of mitochondrial activity and density, suggested an overwhelming of organisms. This study pointed to the importance of considering time of exposure to natural factor variations in tolerance window of organisms in a long-term changing environment. The apparent short-term tolerance of D. polymorpha could hide much more deleterious consequences, i.e. mortality, if abiotic stresses persist, as suggested by climate change models.

Top-down and bottom-up control of phytoplankton communities by zebra mussels Dreissena polymorpha (Pallas, 1771).

Zebra mussels (ZM), Dreissena polymorpha (Pallas, 1771), are one of the most aggressive invasive species. ZM have a strong bidirectional impact on phytoplankton because of their high nutrient excretion rates and high grazing pressure. Furthermore, the interactions between excretion and selective grazing are related to the trophic status of a waterbody and could cause unpredictable changes in phytoplankton. We performed three types of experiments: (i) bottom-up where we measured ZM excretion rates; (ii) top-down where we analyzed the effects of ZM on phytoplankton taxonomic structure via grazing in different trophic conditions; (iii) mesocosm experiment where we estimated the combined top-down and bottom-up effects of ZM on phytoplankton assemblages under different trophic conditions. Our first experiment confirmed high excretion rates of dissolved nutrients (PO43- and NH4+) and dissolved organic carbon (DOC) by ZM. The other experiments revealed selective grazing by ZM, where diatoms were mostly selectively rejected, while green algae were preferred. In the top-down experiment, ZM decreased the total biomass of phytoplankton, while in mesocosm experiments where top-down and bottom-up controls acted simultaneously, we observed increased phytoplankton biomass mainly through increases in filamentous green algae. Our experiments show that ZM can influence phytoplankton through a combination of bottom-up and top-down effects that vary with trophic state.

Species invasions shift microbial phenology in a two-decade freshwater time series.

Invasive species impart abrupt changes on ecosystems, but their impacts on microbial communities are often overlooked. We paired a 20 y freshwater microbial community time series with zooplankton and phytoplankton counts, rich environmental data, and a 6 y cyanotoxin time series. We observed strong microbial phenological patterns that were disrupted by the invasions of spiny water flea (Bythotrephes cederströmii) and zebra mussels (Dreissena polymorpha). First, we detected shifts in Cyanobacteria phenology. After the spiny water flea invasion, Cyanobacteria dominance crept earlier into clearwater; and after the zebra mussel invasion, Cyanobacteria abundance crept even earlier into the diatom-dominated spring. During summer, the spiny water flea invasion sparked a cascade of shifting diversity where zooplankton diversity decreased and Cyanobacteria diversity increased. Second, we detected shifts in cyanotoxin phenology. After the zebra mussel invasion, microcystin increased in early summer and the duration of toxin production increased by over a month. Third, we observed shifts in heterotrophic bacteria phenology. The Bacteroidota phylum and members of the acI Nanopelagicales lineage were differentially more abundant. The proportion of the bacterial community that changed differed by season; spring and clearwater communities changed most following the spiny water flea invasion that lessened clearwater intensity, while summer communities changed least following the zebra mussel invasion despite the shifts in Cyanobacteria diversity and toxicity. A modeling framework identified the invasions as primary drivers of the observed phenological changes. These long-term invasion-mediated shifts in microbial phenology demonstrate the interconnectedness of microbes with the broader food web and their susceptibility to long-term environmental change.

Comparative immune responses of blue mussel and zebra mussel haemocytes to simultaneous chemical and bacterial exposure.

Biomonitoring at the scale of the aquatic continuum and based on biomarkers, requires various representative species and a knowledge of their sensitivity to contaminants. Mussel immunomarkers are established tools for evaluating immunotoxic stress, but little is known about the consequences of an immune activation by local microorganisms on their response to pollution. This study aims to compare the sensitivity of cellular immunomarkers in two mussel species from different environments, the marine mussel Mytilus edulis (blue mussel) and the freshwater mussel Dreissena polymorpha (zebra mussel), to chemical stressors combined with bacterial challenge. Haemocytes were exposed ex vivo to the contaminants (bisphenol A, caffeine, copper chloride, oestradiol, ionomycin) for 4 h. The chemical exposures were coupled with simultaneous bacterial challenges (Vibrio splendidus and Pseudomonas fluorescens) to trigger activation of the immune response. Cellular mortality, phagocytosis efficiency and phagocytosis avidity were then measured by flow cytometry. The two mussel species had different basal levels since D. polymorpha showed higher cell mortality than M. edulis (23.9 ± 11% and 5.5 ± 3% dead cells respectively), and lower phagocytosis efficiency (52.6 ± 12% and 62.2 ± 9%), but similar phagocytosis avidity (17.4 ± 5 and 13.4 ± 4 internalised beads). Both bacterial strains led to an increase in cellular mortality (+8.4% dead cells in D. polymorpha, +4.9% in M. edulis), as well an activation of phagocytosis (+9.2% of efficient cells in D. polymorpha, +6.2% efficient cells and +3 internalised beads per cell in M. edulis). All chemicals triggered an increase in haemocyte mortality and/or phagocytotic modulations, except for bisphenol A. The two species differed in the amplitude of their response. The addition of a bacterial challenge significantly altered cell responses to chemicals with synergetic and antagonistic variations compared to a single exposure, depending on the compound used and the mussel species. This work highlights the species-specific sensitivity of mussel immunomarkers to contaminants, with or without bacterial challenge, and the necessity of considering the presence of in natura non-pathogenic microorganisms for future in situ applications of immunomarkers.

Patterns of dreissenid mussel invasions in western US lakes within an integrated gravity model framework.

Freshwater invasive species, such as the quagga mussel (Dreissena rostriformis bugensis), are causing over $1 billion USD annually in damages to water infrastructure, recreation, and the environment. Once established, quagga and other dreissenid mussels are extremely difficult to eradicate. Preventing the spread of these invasives is critical and of high management concern. Invasive dreissenid establishment is predicated upon both successful dispersal from a source and suitable habitat in the uninfested waterbody to which they are transported. Recreational boaters have become predominant dispersal vectors making it possible to forecast the risk of invasion of waterbodies for more targeted management and prevention. We developed an integrated mussel dispersal model that couples a constrained gravity model and habitat suitability model to forecast future invasions. The model simulates boater movement between lakes, the likelihood of boats transporting mussels, and the likelihood that those mussels survive in the environmental conditions of the new lake. Model output was most sensitive to changes in boater threshold, then buffer zones, while not as sensitive to changes in habitat suitability. From an initial infested source pool of 11 among 402 Western inland US lakes, we forecast additional lakes infested in several possible simulation scenarios. Constraining movement reduced connectivity between waterbodies with amplifying effects at different distance levels. This model can be used to determine waterbodies most at risk for dreissenid mussel invasion and to highlight the importance of multifactor integrated models in environmental management.

Declines in freshwater mussel density, size and productivity in the River Thames over the past half century.

A pioneering, quantitative study published in Journal of Animal Ecology in 1966 on freshwater mussel populations in the River Thames, UK, continues to be cited extensively as evidence of the major contribution that mussels make to benthic biomass and ecosystem functioning in global river ecosystems. Ecological alteration, as well as declines in freshwater mussel populations elsewhere, suggest that changes to mussel populations in the River Thames are likely to have occurred over the half century since this study. We resurveyed the site reported in Negus (1966) and quantified the changes in mussel population density, species composition, growth patterns and productivity. We found large declines in population density for all unionid species. The duck mussel Anodonta anatina decreased to 1.1% of 1964 density. The painter's mussel Unio pictorum fell to 3.2% of 1964 density. The swollen river mussel Unio tumidus showed statistically nonsignificant declines. In contrast to 1964, in 2020 we found no living specimens of the depressed river mussel Pseudanodonta complanata (classified as Vulnerable by the IUCN Red List) but found new records of the invasive, nonnative zebra mussel Dreissena polymorpha and Asian clam Corbicula fluminea. Additionally, we found strong decreases in size-at-age for all species, which now grow to 65-90% of maximum lengths in 1964. As a result of reduced density and size, estimated annual biomass production fell to 7.5% of 1964 levels. Since mussels can be important to ecosystem functioning, providing key regulating and provisioning services, the declines we found imply substantial degradation of freshwater ecosystem services in the River Thames, one of the UK's largest rivers. Our study also highlights the importance to conservationists and ecologists of updating and validating assumptions and data about wild populations, which in the present era of anthropogenic ecosystem alteration are undergoing significant and rapid changes. Regular population surveys of key species are essential to maintain an accurate picture of ecosystem health and to guide management.