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The introduction of non-indigenous organisms in new areas in the context of host-parasite interactions is still poorly understood. This study aimed at a parasitological and histopathological comparison of two phylogenetically distinct forms of the freshwater snail Theodoxus fluviatilis in the River Rhine system: the native Northern-European form, which showed a decline for unknown reasons and is nowadays extinct in the River Rhine, and the non-indigenous Danubian form, which was introduced via the Main–Danube canal. We histopathologically examined populations of Northern-European T. fluviatilis from three smaller rivers of the Rhine system and of Danubian T. fluviatilis from the River Rhine, after confirming the phylogenetic background of the respective population genetically. Results showed differences in the prevalence of trematodes and histopathologic organic alterations between the two snail forms. Both were infected with an opecoelid trematode Plagioporus cf. skrjabini, whereby its prevalence was significantly higher in the Northern-European than in the Danubian form. The parasitic trematode is, to our knowledge, a new trematode species in the River Rhine system, presumably co-introduced through the invasion of its second intermediate and final hosts, i.e. Ponto-Caspian amphipods and gobies. Its impact on native populations of Northern-European T. fluviatilis needs to be subject of future studies.

The various uses of copper or copper compounds in industrial, biocidal or pesticidal products lead to inputs of the metal into aquatic environments. To assess effects of copper ions on non-target organisms, the freshwater snail Theodoxus fluviatilis was used as test organism for a three-week laboratory experiment. Snails were exposed to four copper concentrations ranging from 4 to 39 µg Cu2+/L, and besides mortality, several sublethal parameters were evaluated. Concerning survival, an aqueous copper concentration of 6 µg/L was determined as NOEC, and 16 (± 0.1) µg/L as LC50. Negative sublethal effects on reproduction, activity and pathological modifications in the snails were detected in the treatment with an aqueous copper concentration of 15 µg/L. Our results using T. fluviatilis as a mere grazer exclusively feeding on biofilms contribute to findings that field relevant copper concentrations have a significant effect on non-target organisms in aquatic environments.

The Baltic Sea is one of the most polluted seas in the world, with widespread eutrophication and radionuclide contamination. Using key species of the Baltic Sea, the effects of eutrophication on uptake and trophic transfer of the radioactive micronutrients commonly found in nuclear power plant effluents were investigated experimentally using the brown macroalgae Fucus vesiculosus and the grazers Idotea balthica and Theodoxus fluviatilis in a controlled environment. Rapid uptake of 54 Mn, 57 Co, and 65 Zn from water was observed in all biota; and eutrophication combined with grazing pressure strongly influenced the uptake in F. vesiculosus. Uptake of 54 Mn, 57 Co, and 65 Zn to I. balthica and T. fluviatilis grazing on F. vesiculosus were also observed. The results indicate that ecosystems could be open for further trophic transfer as radionuclides accumulate quickly in the producers and are transferred to primary consumers. Environ Toxicol Chem 2021;40:1694-1705. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The widely distributed snail species Theodoxus fluviatilis (Linneaus, 1758) is rather diverse in shell size and patterning. It has formed regional subgroups in northern Germany that appear separate in either fresh- or brackish water, yet, according to literature, are indistinguishable by morphology, anatomy or mtRNA markers. Tolerance towards challenging salinities, however, is distinct. The question as to whether the observed difference in salinity tolerance is a result of local adaptation or of phenotypic plasticity remains. In this study, physiological limits to salinity stress and tolerance shift abilities were compared between individuals from both subgroups in a salinity transfer experiment and acclimation regime followed by a survival analysis. Brackish water animals struggled in freshwater but performed much better than freshwater individuals when directly transferred into higher salinities. With acclimation to their challenging salinities, individuals of both subgroups achieved shifts in the slopes of their reaction norms and were able to survive salinity levels otherwise lethal to them. Even with this shift freshwater animals were not able reach the tolerance levels of brackish water individuals. The results indicate that phenotypic plasticity as well as genetic adaptation may determine osmotolerance in regional subgroups of T. fluviatilis.

The paper discusses results of sedimentological, faunal (molluscs, ostracods) and geochemical studies of an 80-cm-thick rhythmite succession within a glaciolacustrine sequence (8–10 m in thickness) of the Ławki Formation exposed at the Parchliny C site, in the tectonically active Kleszczow Graben, central Poland. Sedimentological studies show the predominance of rhythmically deposited pale grey muds (2.0–7 cm thick) and black clays (0.5–5 cm thick). The pro-glacial sediments have yielded the first examples of Saalian molluscan and ostracod communities to be recorded from Europe and probably globally. The presence of a lake basin is confirmed by the freshwater species fauna: Candona neglecta, Cypridopsis vidua, Fabaeformiscandona protzi, Limnocythere inopinata, Limnocytherina sanctiparicii Cyclocypris laevis, Metacypris cordata (ostracods) and Anodonta cygnaea, Ancylus fluviatilis, Theodoxus fluviatilis, Bithynia tentaculata, Valvata piscinalis and Pisidium sp. (molluscs), suggestive of deposition during a period of colder climatic conditions, although some species might be indicative of a warmer period, resembling an interglacial. The whole section has a high carbonate content, up to several tens percent. The carbonates are enriched in the heavy isotope of oxygen. The isotopic composition of carbon and oxygen indicates two stages of lake development. The transition of the lake from a hydrologically open to a closed system with significant evaporation has been reconstructed from correlation of δ13C and δ18O. Sedimentological, faunal (molluscs, ostracods) and stable-isotope studies of the Saalian Ławki Formation have revealed an important snapshot – a 14-year record in the hydrological transformation of this specific pro-glacial lake system.

This study focuses on the inter- and intra-specific variability in δ13C and δ18O values of shells and opercula of gastropods sampled live from the littoral zone of Lake Lednica, western Poland. The δ13C and δ18O values were measured in individual opercula of Bithynia tentaculata and in shells of Bithynia tentaculata, Gyraulus albus, Gyraulus crista, Lymnaea sp., Physa fontinalis, Radix auricularia, Theodoxus fluviatilis and Valvata cristata. The gastropods selected for the study are among the species most commonly found in European Quaternary lacustrine sediments. The carbon isotope composition of the gastropod shells was species-specific and the same order of species from the most to the least13C-depleted was observed at all sites sampled. Differences in shell δ13C values between species were similar at all sampling sites, thus the factors influencing shell isotopic composition were interpreted as species-specific. The δ18O values of shells were similar in all the species investigated. Significant intra-specific variability in shell δ13C and δ18O values was observed not only within the populations of Lake Lednica, which can be explained by heterogeneity of δ13C DIC, δ18O water and water temperature between the sites where macrophytes with snails attached were sampled, but also between individuals sampled from restricted areas of the lake’s bottom. The latter points to the importance of factors related to the ontogeny of individual gastropods.

The round goby Neogobius melanostomus has successfully invaded much of the Baltic Sea. However, very little is known about the feeding habits of the species in this newly invaded environment. Our laboratory experiment showed that the round goby is able to effectively consume a diverse variety of prey when given the choice between dominant benthic invertebrates: bivalves (Macoma balthica, Mytilus trossulus, Cerastoderma glaucum) and amphipods (Gammarus spp.). In contrast consumption of the gastropod (Theodoxus fluviatilis) was very low in all provided combinations. Nevertheless, the round goby had no statistically significant preference towards any of the prey taxa. The round goby exhibited size-specific consumption of M.trossulus, with smaller individuals being consumed at least 25% more than larger size classes. In addition elevated prey density resulted in higher consumption of prey by the fish. The broad diet suggests that shifting densities of benthic invertebrate prey has little influence on the further dispersal of the round goby in the Baltic Sea as the species is potentially able to switch between several native invertebrate taxa. This opportunistic feeding behaviour has likely favoured this invasion and ensured success of the species in the invaded ecosystem.

Hyperosmotic stress may result in osmotic volume loss from the body to the environment in animals which cannot control the water permeability of their integument. Euryhaline (having a wide tolerance range of environmental salinities) animals have generally evolved the ability to counteract cell volume shrinkage by accumulating inorganic and organic osmolytes within their cells to balance internal and external osmolalities. Molluscs use very different combinations of amino acids and amino acid derivatives to achieve this goal. Theodoxus fluviatilis (Linneaus, 1758) is a neritid gastropod that is distributed not only in limnic habitats in Europe but also in brackish waters (e.g. along the shore line of the Baltic Sea). Animals from brackish sites survive better in high salinities than animals from freshwater locations. The results of this study indicate that these differences in salinity tolerance cannot be explained by differences in the general ability to accumulate amino acids as organic osmolytes. Although there may be differences in the metabolic pathways involved in osmolyte accumulation in foot muscle tissue, both groups of animals accumulate amino acid mixtures equally well when stepwise acclimated to their respective maximum tolerable salinity for extended periods. Among these amino acids, alanine, proline as well as the osmolyte urea hold a special importance for cell volume preservation in Theodoxus under hyperosmotic stress. It is possible that the accumulation of various amino acids during hyperosmotic stress occurs via hydrolysis of storage proteins, while alanine and proline are most likely newly synthesised under conditions of hyperosmotic stress in the animals.

Uranium mining is an environmental concern because of runoff and the potential for toxic effects on the biota. To investigate uranium toxicity to freshwater invertebrates, we conducted a 96-h acute toxicity test to determine lethal concentrations (testing concentrations up to 262 mg L−1) for three stream invertebrates: a shredder caddisfly, Schizopelex festiva Rambur (Trichoptera, Sericostomatidae); a detritivorous isopod, Proasellus sp. (Isopoda, Asellidae); and a scraper gastropod, Theodoxus fluviatilis (Gastropoda, Neritidae). Next, we ran a chronic-toxicity test with the most tolerant species (S. festiva) to assess if uranium concentrations found in some local streams (up to 25 μg L−1) affect feeding, growth and respiration rates. Finally, we investigated whether S. festiva takes up uranium from the water and/or from ingested food. In the acute test, S. festiva survived in all uranium concentrations tested. LC50-96-h for Proasellus sp and T. fluviatilis were 142 mg L−1 and 24 mg L−1, respectively. Specimens of S. festiva exposed to 25 μg L−1 had 47% reduced growth compared with specimens under control conditions (21.5 ± 2.9 vs. 40.6 ± 4.9 μg of mass increase animal−1·day−1). Respiration rates (0.40 ± 0.03 μg O2·h−1·mg animal−1) and consumption rates (0.54 ± 0.05 μg μg animal−1·day−1; means ± SE) did not differ between treatments. Under laboratory conditions S. festiva accumulated uranium from both the water and the ingested food. Our results indicate that uranium can be less toxic than other metals or metalloids produced by mining activities. However, even at the low concentrations observed in streams affected by abandoned mines, uranium can impair physiological processes, is bioaccumulated, and is potentially transferred through food webs.

Freshwater environments are the route through which inland plastics are transported to the ocean, explaining why the number of freshwater microplastic (MP) studies has recently been increasing. Despite the lack of recycling and the presence of severe plastic pollution in many African countries, MPs have been scarcely reported in African freshwaters and the current study gives the first empirical account for West Africa. The study investigates MP pollution in an important West African river system (Osun River system, Nigeria) and gives an insight into microplastic contamination in a main European river (Rhine River), using gastropods which are potential consumers of MPs, from both systems. From the Osun River system, the most common gastropods (Lanistes varicus and Melanoides tuberculata) were analysed for MP contamination. Two MP types (fibre and film) were recorded in L. varicus, whereas only fibre was recorded in M. tuberculata. Micro-Fourier-transform infrared spectroscopy (μFTIR) revealed that the MP films in the African gastropods were made of polyethylene and strongly resembled black polyethylene bags that covered the Osun River banks. From the Rhine River, the gastropod Theodoxus fluviatilis was analysed and nylon as well as polypropylene fibres were found. In both systems (Osun River and Rhine River), fibre was the dominant MP type. In conclusion, the study shows that MP contamination in Nigeria, a West African country with a lack of recycling and poor waste management practice, is reflected in two different local gastropod species. Furthermore, the comparison with a European gastropod species shows that fibres are the dominant MP type in gastropods from both freshwater systems. In both systems, MPs ingested by the gastropods could be transferred to higher trophic levels following predation. We therefore recommend that more empirical studies should be carried out along different feeding guilds of African freshwater invertebrates and fish. When MPs are transferred to fish, MPs may reach humans through fish consumption.

Contaminant-driven feeding inhibition has direct and immediate consequences at higher levels of biological organization, by depressing the population consumption and thus hampering ecosystem functioning (e.g., grazing, organic matter decomposition). The present study aimed at developing a short-term laboratory and in situ assay based on the postexposure feeding of the freshwater snail Theodoxus fluviatilis. A method to precisely quantify feeding rates was first developed, consisting of a 3-h feeding period, in darkness, on 150 defrosted nauplii of the brine shrimp Artemia franciscana. Postexposure feeding after a 48-h exposure to cadmium was approximately as sensitive as survival, with the median effective concentration (EC50) and median lethal concentration (LC50) being 85 µg/L and 102 µg/L, respectively, and the 20% effective concentration (EC20) and 20% lethal concentration (LC20) being 41 µg/L and 77 µg/L, respectively. Together, both effects at the LC20 reduced population consumption by 56%. In situ experiments at reference sites covering broad ranges of current velocity, hardness, conductivity, sediment organic matter content, and sediment particle size distribution revealed the influence of these abiotic conditions on postexposure feeding, in the absence of contamination, to be negligible. The effectiveness of the in situ assay was evaluated at 5 sites contaminated with acid mine drainage. Surviving organisms at the single partially lethal site (37% mortality) presented a 54% feeding inhibition relative to the reference, whereas the population consumption would be inhibited by 71%, confirming the integration of survival and feeding to be pertinent for estimating contaminant effects at higher levels of biological organization. Environ Toxicol Chem 2013;32:2144–2152. © 2013 SETAC

The relationship between the δ13C of dissolved inorganic carbon (DIC) and modern mollusk aragonite from rivers was calibrated for the purpose of reconstructing DIC paleochemistry from the shell record. The δ13C values of aragonitic bivalves (Dreissena polymorpha, Corbicula fluminea), prosobranch gastropods (Bithynia tentaculata, Theodoxus fluviatilis, Viviparus viviparus), and an air-breathing pulmonate gastropod (Limnea auricularia) were analyzed from several locations on the Rhone River (—13.7‰ to —6.0‰) and its major tributary, the Saone River (—11.4‰ to —10.2‰). The δ13CDIC varied from —11.5‰ to —7.5‰, and the δ13C of particulate inorganic matter (POM) varied from —31.7‰ to —25.4‰. At a given site, the δ13C of all species except the pulmonate were within 1‰ of each other. Whole-shell δ13C correlated positively with δ13CDIC, with a slope close to unity. Bioaragonite—DIC fractionations were 0–1.5‰ for bivalves and 0–2.7‰ for gastropods (excluding the pulmonates). Applying these fractionations, bivalves that live in open water are a reliable proxy, monitoring the average δ13CDIC value to within its natural ~2‰ temporal variation within the growth period. For the suspension feeders (bivalves) using POM as a food source, the δ13C of whole shells and bulk POM indicated that the incorporation of carbon derived from respiratory sources lay in the range 10–30%. Fine-scale analyses of growth increments of C. fluminea could not be related simply to δ13CDIC because metabolic and seasonal variations in δ13CDIC produced similar isotopic fluctuations (≤2.5‰).

Nutrient enrichment in coastal marine systems can have profound impacts on trophic networks. In the Baltic Sea, the population of Great Cormorant (Phalacrocorax carbo sinensis) has increased nearly exponentially since the mid-1990 s, and colonies of these seabirds can be important sources of nitrogen enrichment for nearby benthic communities due to guano runoff. In this study we used stable isotope analyses and diet mixing models to determine the extent of nitrogen enrichment from cormorant colonies, as well as to examine any possible changes in herbivore diet preferences due to enrichment. We found significantly higher levels of δ(15)N in samples from colony islands than control islands for producers (the dominant macroalga Fucus vesiculosus, filamentous algae, and periphyton) and herbivores, as well as a positive correlation between enrichment and nest density in colony sites. We also found that enrichment increased over the breeding season of the cormorants, with higher enrichment in late summer than early summer. While the amount of total nitrogen did not differ between colony and control sites, the amount of guano-based nitrogen in algae was >50% in most sites, indicating high nitrogen enrichment from colonies. Herbivores (the isopod Idotea balthica and the gastropod Theodoxus fluviatilis) preferred feeding upon the dominant macroalga Fucus vesiculosus rather than on filamentous algae or periphyton in both control and colony, and there was a significant increase in periphyton consumption near colony sites. Overall, guano from cormorant colonies seems to have effects on both producers and herbivores, as well as the potential to modify algae-herbivore interactions.

The euryhaline gastropod Theodoxus fluviatilis is found in northern Germany in freshwater or in brackish water habitats in the Baltic Sea. Previous studies have revealed that individuals from both habitats are not distinguishable by morphological characters or by sequence comparison of DNA encoding 16S RNA or cytochrome C. As reported in this study, animals collected in the two habitats differ substantially in their physiological ability to adapt to different salinities. Comparison of accumulation rates of ninhydrin-positive substances (NPS) in foot muscle upon transfer of animals to higher medium salinities revealed that brackish water animals were perfectly able to mobilize NPS, while freshwater animals had only limited ability to do so. In an attempt to explore whether this difference in physiology may be caused by genetic differentiation, we compared protein expression patterns of soluble foot muscle proteins using 2D gel electrophoresis and silver staining. Of the 40 consistently detected protein spots, 27 showed similar levels in protein expression in animals collected from freshwater or brackish water habitats, respectively. In 12 spots, however, protein concentration was higher in brackish water than in freshwater animals. In four of these spots, expression levels followed increases or decreases in medium salinities. In a different set of 4 of these 12 spots, protein levels were always higher in brackish water as compared to freshwater animals, regardless of their physiological situation (14 days in artificial pond water or in medium with a salinity of 16 per thousand). The remaining 4 of the 12 spots had complex expression patterns. Protein levels of the remaining single spot were generally higher in freshwater animals than in brackish water animals. These expression patterns may indicate that freshwater and brackish water animals of T. fluviatilis belong to different locally adapted populations with subtle genetic differentiation.

Contaminants are important stressors in the aquatic environment and may exert selective pressures on organisms. We hypothesized that snails originating from a metal-contaminated habitat (B) would have increased tolerance to harbour contaminants (e.g. metals from antifouling paints), compared to snails originating from a relatively clean habitat (A). We assessed tolerance to metals in terms of survival and histopathological alterations after 2, 4 and 8 weeks of in situ exposure in three Baltic Sea boat harbours and three reference sites. We also hypothesized that any potential tolerance to contaminants would be associated with differences in genetic diversity between the two snail populations (evaluated as mitochondrial cytochrome c oxidase subunit I, COI). The results show that snails from population A survived to a higher extent compared to population B, possibly indicating either a lack of adaptation to metals in snails B or impaired health condition due to contaminant pre-exposure or a higher resilience of snails A. Moreover, the genetic diversity of COI was low within each population and did not differ between populations. In general, 83% of all the types of histopathological alterations (e.g. lysis and necrosis of gonads and digestive gland or granulocytoma and phagocytosis in the storage tissue, among others) had a higher probability of occurrence among harbour-exposed snails compared to reference-exposed snails, regardless of snail population origin. The only significant difference in histological effects between the two populations was in the frequency of parasite infestations and shell fouling, both being larger for population A than B. Interestingly, the rate of parasite infestations was higher for males than females from population A, whereas no sexual dichotomy was observed for population B. Our results show that exposure to harbour contaminants causes both lethal and sublethal toxicity to snails, and the association between many of the toxic responses and metals substantiates that antifouling substances contribute to the observed effects, although there is a large proportion of variation in our data that remains unexplained.

Harbours with limited water exchange are hotspots of contaminant accumulation. Antifouling paints (AF) contribute to this accumulation by leaching biocides that may affect non-target species. In several leisure boat harbours and reference areas in the Baltic Sea, chronic exposure effects were evaluated using caging experiments with the snail Theodoxus fluviatilis. We analysed variations in ecologically relevant endpoints (mortality, growth and reproduction) in concert with variation in metallothionein-like proteins (MTLP) levels. The latter is a biomarker of exposure to metals, such as copper (Cu) and zinc (Zn), which are used in AF paints as active ingredient and stabilizer, respectively. In addition, environmental samples (water, sediment) were analysed for metal (Cu and Zn) and nutrient (total phosphorous and nitrogen) concentrations. All life-history endpoints were negatively affected by the exposure, with higher mortality, reduced growth and lower fecundity in the harbours compared to the reference sites. Metal concentrations were the key explanatory variables for all observed adverse effects, suggesting that metal-driven toxicity, which is likely to stem from AF paints, is a source of anthropogenic stress for biota in the harbours.