Invading the invaders: reproductive and other mechanisms mediating the displacement of zebra mussels by quagga mussels

Responses of zebra and quagga mussels to copper and tribytiltin exposure: Bioconcentration, metabolic and cardiac biomarkers

One of the top ecological priorities is to find sensitive indicators for pollution monitoring. This study focuses on the bioconcentration and responses (condition index, survival, oxygen consumption, heart rates, and oxidative stress and neurotoxic effect biomarkers) of mussels from the Volga River basin, Dreissena polymorpha and Dreissena bugensis, to long-term exposure to toxic chemicals such as tributyltin (TBT, 25 and 100 ng/L) and copper (Cu, 100 and 1000 μg/L). We found that TBT was present in the tissues of zebra and quagga mussels in comparable amounts, whereas the bioconcentration factor of Cu varied depending on its concentration in water. Differences in responses between the two species were revealed. When exposed to high Cu concentrations or a Cu-TBT mixture, quagga mussels had a lower survival rate and a longer heart rate recovery time than zebra mussels. TBT treatment caused neurotoxicity (decreased acetylcholinesterase activity) and oxidative stress (increased levels of thiobarbituric acid reactive substances) in both species. TBT and Cu levels in mussel tissues correlated positively with the condition index, but correlated with the level of acetylcholinesterase in the mussel gills. The principal component analysis revealed three main components: the first consists of linear combinations of 14 variables reflecting TBT water pollution, TBT and Cu levels in mussel tissues, and biochemical indicators; the second includes Cu water concentration, cardiac tolerance, and mussel size; and the third combines weight, metabolic rate, and heart rates. Quagga mussels are less tolerable to contaminants than zebra mussels, so they may be used as a sensitive indicator.

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.

Salinity and pH effects on survival, growth, and reproduction of quagga mussels

Background

In recent decades, invasive quagga mussels have expanded to the Western United States from the Great Lakes region of North America. Most studies that evaluate the invasion potential of quagga mussels in western water bodies have utilized physiological and life history information from zebra mussels, a related taxon. Few studies have assessed the potential for invasion using specific information from quagga mussel life history or experiments that test for their survival in the fresh and saline waters of the western United States.

Methods

We investigated quagga mussel survival, growth, and reproduction using semi-natural experiments under temperature and light controlled conditions across a gradient of water salinity (fresh to brackish) and pH (8.4-11). Water from Lake Mead was used as a positive control in our experiment, and water from Pyramid Lake and the Truckee River was used as brackish and freshwater treatments, respectively. The mussels used in the experiments were collected from Lake Mead.

Results

After 12 h in brackish water (4 ppt, pH 9.3), we observed 100% mortality of adult mussels. The swelling and disintegration of body tissues and high mortality rates indicated that high potassium, sodium, and chloride concentrations were the likely causes of death in brackish water treatments. In contrast, mussels were able to survive, grow, and reach sexual maturity in freshwater (0.1 ppt) with a low calcium concentration (17 mg L^-1) after 57 days. Mussels died after 2 days at pH 11 and after 12 days at pH 10; during the 14-day monitoring period, no mortality was detected at pH 9.0, 9.3, or 9.5 and mussels did not exhibit any visual indications of stress. Understanding quagga mussel physiological and environmental tolerances appears to be essential for assessing their invasion potential in aquatic habitats.

Dreissenids’ breaking loose: differential attachment as a possible driver of the dominance shift between two invasive mussel species

Ponto-Caspian dreissenids are notorious freshwater invaders. Recently, widespread observations show a dominance shift from the early invader, Dreissena polymorpha, to its successor, Dreissena bugensis. These observations likely reflect congeneric species differences in physiological and behavioural traits. Here, we assessed the mussel attachment strength, attachment rate, and the mode of byssal failure as trait differences that could potentially contribute to dominance shifts. The attachment traits were measured in field and laboratory experiments. Fouling plates were deployed in the Rhine-Meuse river delta and dreissenids were collected and acclimatised in 60 L non-aerated freshwater tanks. Attachment strength was positively correlated with shell size. The attachment strength of D. bugensis was significantly greater compared to slower growing D. polymorpha individuals of a dreissenid field assemblage. This corresponded to the superior byssal thread morphology of D. bugensis (i.e. higher number and two times wider byssal threads). Moreover, our results indicated that byssal threads of D. bugensis are stronger than those of D. polymorpha, as the latter ruptured more often. Additionally, D. bugensis had a significantly lower attachment rate than D. polymorpha. Having a greater attachment strength gives D. bugensis an advantage when it comes to withstanding currents and predators. On the other hand, not being attached allows an individual to actively move around. This would allow them to move away from fast changing unfavourable environmental conditions. These attachment traits indicate competitive benefits for D. bugensis over D. polymorpha, therefore possibly contributing to the dominance shifts.

Cyanobacteria reduce motility of quagga mussel (Dreissena rostriformis bugensis) sperm

The temporal expansion of harmful algal blooms, primarily associated with cyanobacteria, may impact aquatic organisms at vulnerable life-history stages. Broadcast spawning species release gametes into the water column for external fertilization, directly exposing sperm to potential aquatic stressors. To determine if cyanobacteria can disrupt reproduction in freshwater broadcast spawners, we evaluated sublethal effects of cyanobacteria exposure on quagga mussel (Dreissena rostriformis bugensis) sperm. In laboratory studies, sperm were collected after inducing mussels to spawn using serotonin and exposed to 11 cultures of cyanobacteria including Anabaena flos-aquae, Aphanizomenon flos-aquae, Dolichospermum lemmermannii, Gloeotrichia echinulata, 5 cultures of Microcystis aeruginosa, M. wesenbergii, and Planktothrix suspensa. Sperm motility, using endpoints of cumulative distance traveled and mean velocity, was calculated for a minimum of 10 individual sperm using a novel optical biotracking assay method. The distance and velocity at which sperm traveled decreased when exposed to Aphanizomenon flos-aquae and 2 M. aeruginosa cultures. Our findings indicate that cyanobacteria impede the motility of quagga mussel sperm, which can potentially result in reproductive impairments to mussels and potentially other broadcast spawning species. Environ Toxicol Chem 2019;38:368-374. © 2018 SETAC.

Energy allocation in two dreissenid species under metal stress

Measurements of biological responses on living organisms are essential in aquatic biomonitoring. In freshwaters, Dreissena polymorpha is an invasive bivalve commonly used in ecotoxicological studies and considered as a model organism. However, D. polymorpha abundances are declining while another species colonizes most of the freshwaters: Dreissena rostriformis bugensis. This species has already been studied in ecophysiology but there is still a lack of data concerning its responses to stressors before its use as a bioindicator of environmental pollution. This study aims to compare the responses of the two species exposed to metal stress. Responses at different levels of biological organization were targeted with measurement of sub-cellular and individual biomarkers following an exposure of up to 7 days to cadmium at 10 μg.L^-1. At the individual level, the scope for growth (SFG) was measured. It corresponds to the energy allocated to growth and reproduction. D. polymorpha exhibits variations in biomarker measurements as well as in the SFG in presence of Cd. D. r. bugensis shows no variation in its responses at the different targeted levels. According to the present results, energy metabolism seems to have an essential role for these species when facing a metal stress. Different energy allocation strategies were evidenced between the two species, although the link with biochemical biomarkers is more evident for D. polymorpha than for D. r. bugensis.

Impact of multiple stressors on biomarker responses in sympatric dreissenid populations

Dreissenid mussels, well-known invaders of the northern hemisphere, also constitute good biomonitors for freshwater quality assessment. Whereas the oldest, Dreissena polymorpha, is relatively well-known, the new invasive, Dreissena rostriformis bugensis, has been very little characterized. The aim of this study was to compare subcellular biomarker responses within these species, by taking into account inter- and intra-specific variability in biomarker responses during a multi-stress assessment. Indeed, due to local environmental conditions and genetic background, biomarker responses can be different between populations of a given species, not only between species. To evaluate these differential responses, we sampled mussels on two sites where they are both present in sympatry (plus another D. r. bugensis population), and we exposed these populations in laboratory to different stressors: thermal stress (12 or 17 °C), dietary stress (fed or unfed), contamination (nickel at 0, 20 and 500 μg L^-1) and exposure duration (0, 4 or 8 days). Results mainly evidenced strong inter-species and inter-population differences, underlining the need to discriminate correctly between the two species and to know well the populations used in biomonitoring. Results also evidenced thermal and food stress-related effects. The numerous data obtained during this multi-stress experiment also highlight the complexity of working on several stressors and analysing the associated results.

Multilocus phylogeny of the zebra mussel family Dreissenidae (Mollusca: Bivalvia) reveals a fourth Neotropical genus sister to all other genera

Dreissenidae is one of the most economically and ecologically important families of freshwater and estuarine mollusks. Fourteen extant species and three genera are currently recognized: Congeria contains three species from karst caves along the eastern Adriatic coast and one from the Orinoco River of Venezuela, Dreissena contains six species native to Eastern European rivers and estuaries, and Mytilopsis contains three species from the Gulf of Mexico, Caribbean, and northwestern coast of South America and one from the Tocantins River of Brazil. Previous molecular phylogenetic studies have examined all species except those from South American rivers, and found each genus to be monophyletic with Congeria and Mytilopsis forming a clade sister to Dreissena. We present the first multilocus phylogeny of Dreissenidae inclusive of South American riverine species. Bayesian and maximum likelihood analyses of a 3085 bp alignment consisting of mitochondrial (COI and 16S) and nuclear (18S and 28S) gene regions found Neotropical species to be consistently and strongly supported as sister to all other dreissenids, although incomplete sequencing of the single Orinoco specimen obscured Neotropical monophyly. Our intergeneric relationships are inconsistent with an extensive fossil record suggesting that dreissenids originated in Europe approximately 30 My before dispersing to the Western Hemisphere. Fossil-calibrated analyses indicated that Neotropical dreissenids diverged from European lineages in the mid to late Eocene (∼39.3 Ma), and Brazilian and Guiana shield populations diversified during the Oligocene to Miocene. We erect the new genus Rheodreissena for all Neotropical freshwater dreissenids and present haplotype data indicative of at least three species. Widespread anthropogenic alteration of the middle Xingu River and lower Amazon threatens the persistence of these endemic, poorly studied mussels and may facilitate introduction beyond their native range.

Field biomonitoring using the zebra mussel Dreissena polymorpha and the quagga mussel Dreissena bugensis following immunotoxic reponses. Is there a need to separate the two species?

The zebra mussel, Dreissena polymorpha constitutes an extensively used sentinel species for biomonitoring in European and North American freshwater systems. However, this invasive species is gradually replaced in freshwater ecosystem by Dreissena bugensis, a closely related dreissenid species that shares common morphological characteristics but possess some physiological differences. However, few are known about differences on more integrated physiological processes that are generally used as biomarkers in biological monitoring studies. Declining of zebra mussel populations raises the question of the sustainability of using one or both species indifferently to maintain the quality of environmental pollution monitoring data. In our study, we performed a field comparative study measuring immune-related markers and bioaccumulation of PCBs, PAHs and PBDEs in sympatrically occurring mussel populations from three sites of the St. Lawrence River. For tested organisms, species were identified using RFLP analysis. Measurement of bioaccumulated organic compounds indicated a higher accumulation of PCBs and PBDEs in D. bugensis soft tissues compared to D. polymorpha while no differences were noticed for PAHs. Results of hemocytic parameters highlighted that differences of hemocyte distributions were associated to modulations of phagocytic activities. Moreover, marked differences occurred in measurement of hemocytic oxidative activity, indicating divergences between the two species for ROS regulation strategies. This physiological characteristic may deeply influence species responses facing environmental or pollution related stress and induce bias if the two species are not differentiated in further biomarker or bioaccumulation measurement-based studies.

Differentiation of sympatric zebra and quagga mussels in ecotoxicological studies: A comparison of morphometric data, gene expression, and body metal concentrations

The zebra mussel is among the best studied freshwater molluscs in ecotoxicology, but information on the quagga mussel is lacking. Considering its potential spread, we selected a river in France in which zebra and quagga mussels coexisted, and then we used genetic markers to differentiate the two species and compared morphological parameters. cDNA sequencing assays of ten genes already used in zebra mussels were performed on quagga mussels to obtain functional specific primers. Then we analyzed the expression of genes involved in cellular metabolic activities (Cytochrome-c-oxidase - cox, and ATP synthase - atp), detoxification processes (Glutathione-S-Transferase - gst), oxidative stress (Catalase - cat), and digestive functions (Amylase - amy) on the two species. Whereas morphometric analysis underlined similarities in shape between the two species, relative gene expression profiles and metal concentrations evidenced strong differences. Quagga mussels notably presented half as high concentrations in Cd and Pb, two particularly toxic elements, as zebra mussels. These results imply that i) particular attention should be paid to properly distinguish the two species considering their similar external appearance, and ii) zebra mussels cannot be replaced by quagga mussels in ecotoxicological studies without preliminary investigations on biomarker response patterns. To our knowledge, this study is the first to have undertaken such an approach in gene expression analysis in quagga mussels, and more generally to have compared such biomarker responses of zebra and quagga mussels in the field.

Differential tolerance to nickel between Dreissena polymorpha and Dreissena rostriformis bugensis populations

Differential tolerance to stress is partly responsible for the heterogeneity of biomarker responses between populations of a sentinel species. Although currently used for freshwater biomonitoring, studies concerning inter-populational variability in tolerance to contaminants for the zebra mussel (Dreissena polymorpha) are scarce. Moreover, this well-known invader is currently replaced by another, the quagga mussel (Dreissena rostriformis bugensis). To evaluate the differential tolerance between dreissenids, several populations of both species were exposed to a high concentration of nickel. A LT₅₀ (time when 50% of individuals were dead) was established for each population. Biomarker responses and internal nickel concentration were also measured, to link tolerance with physiological status. Results evidenced that D. polymorpha populations are more heterogeneous and more tolerant than D. r. bugensis ones. For D. polymorpha populations only, LT₅₀ values were positively correlated with the nickel contamination in situ, with higher anti-oxidative defences and a higher Integrated Biomarker Response value in the field. Such findings may be explained by local adaptation and invasion dynamic within each species. The significance of this differential tolerance when using biomarker responses for biomonitoring purposes is thus discussed.

Validated methodology for quantifying infestation levels of dreissenid mussels in environmental DNA (eDNA) samples

The zebra mussel (Dreissena polymorpha Pallas, 1771) and the quagga mussel (D. rostriformis Deshayes, 1838) are successful invasive bivalves with substantial ecological and economic impacts in freshwater systems once they become established. Since their eradication is extremely difficult, their detection at an early stage is crucial to prevent spread. In this study, we optimized and validated a qPCR detection method based on the histone H2B gene to quantify combined infestation levels of zebra and quagga mussels in environmental DNA samples. Our results show specific dreissenid DNA present in filtered water samples for which microscopic diagnostic identification for larvae failed. Monitoring a large number of locations for invasive dreissenid species based on a highly specific environmental DNA qPCR assay may prove to be an essential tool for management and control plans focused on prevention of establishment of dreissenid mussels in new locations.

Integrated multi-biomarker responses in two dreissenid species following metal and thermal cross-stress

With current global changes, the combination of several stressors such as temperature and contaminants may impact species distribution and ecosystem functioning. In this study, we evaluated the combined impact of two metals (Ni and Cr) with a thermal stress (from 12 to 17 °C) on biomarker responses in two bivalves, Dreissena rostriformis bugensis and Dreissena polymorpha. Biomarkers are informative tools to evaluate exposure and effects of stressors on organisms. The set of 14 biomarkers measured here was representative of both physiologic (filtration activity) and cellular antioxidant and detoxification mechanisms. Our aim was to study the response pattern of both species, and its meaning in terms of invasive potential. The implications for the use of these mussels in environmental monitoring are also discussed. Results evidenced that the two species do not respond to multiple stressors in the same way. Indeed, the effects of contamination on biomarker responses were more marked for D. polymorpha, especially under nickel exposure. While we cannot conclude as to the effect of temperature, invasiveness could be influenced by species sensitivity to contaminants. The physiological and cellular differences between D. polymorpha and D. r. bugensis might also be of concern for environmental risk assessment. The two species present differential bioaccumulation patterns, filtration activity and cellular biomarker responses. If D. polymorpha populations decline, their substitution by D. r. bugensis for biomonitoring or laboratory studies will not be possible without a deeper understanding of biomarker responses of the new invasive.

Ecosystem transformations of the Laurentian Great Lake Michigan by nonindigenous biological invaders

Lake Michigan, a 58,000-km(2) freshwater inland sea, is large enough to have persistent basin-scale circulation yet small enough to enable development of approximately balanced budgets for water, energy, and elements including carbon and silicon. Introduction of nonindigenous species-whether through invasion, intentional stocking, or accidental transplantation-has transformed the lake's ecosystem function and habitat structure. Of the 79 nonindigenous species known to have established reproductive populations in the lake, only a few have brought considerable ecological pressure to bear. Four of these were chosen for this review to exemplify top-down (sea lamprey, Petromyzon marinus), middle-out (alewife, Alosa pseudoharengus), and bottom-up (the dreissenid zebra and quagga mussels, Dreissena polymorpha and Dreissena rostriformis bugensis, respectively) transformations of Lake Michigan ecology, habitability, and ultimately physical environment. Lampreys attacked and extirpated indigenous lake trout, the top predator. Alewives outcompeted native planktivorous fish and curtailed invertebrate populations. Dreissenid mussels-especially quagga mussels, which have had a much greater impact than the preceding zebra mussels-moved ecosystem metabolism basin-wide from water column to bottom dominance and engineered structures throughout the lake. Each of these non indigenous species exerted devastating effects on commercial and sport fisheries through ecosystem structure modification.