Search

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.

Metal pollution poses a major threat to aquatic systems especially in anthropogenic influenced areas, in as much as metals are persistent in the environment. The freshwater snail Theodoxus fluviatilis has often been used as an indicator species for the ecological status in river monitoring. In the River Rhine, the native Northern-European form of T. fluviatilis is nowadays extinct, whilst the Danubian form is spreading along the river. The aim of our study was to investigate if the cryptic invader is affected by metal exposure present in the River Rhine and to discuss its potential as an indicator for metal pollution. Several environmental abiotic (14 water environmental variables plus five common metal concentrations in water and biofilm) and biotic parameters (biofilm mass) were measured across 23 sites along the River Rhine. Five population and six histopathological parameters were evaluated on snails collected at all 23 sites. Aqueous chromium concentration was positively correlated to the damage of male reproductive organs of T. fluviatilis, and higher ammonium concentration was correlated to a decrease in snail size and an increase in the proportion of juveniles. None of the analysed snail parameters was negatively correlated to concentrations of other metals measured, like copper and zinc. Therefore, based on the parameters evaluated, our results indicate that the Danubian form of T. fluviatilis is only restrictedly suitable as an indicator for metal pollution in the River Rhine system. Further field and laboratory investigations including other stressors are necessary to evaluate the indicator potential of the cryptic invader holistically.

2. Theodoxus fluviatilis (Linnaeus, 1758) Findings in Serbia. Theodoxus fluviatilis: Matoničkin et al. (1975); Karaman (2001, 2012); Jakovčev-Todorović et al. (2005); Paunović et al. (2007a, 2008, 2012 a); Marković et al. (2012, 2013, 2014); Martinović-Vitanović et al. (2013); Tomović et al. (2014). Common name. River nerite. Morphology. Medium-sized species. Oval shaped shell has dimensions up to 13 mm. Colouration pattern is extremely variable, ranging from almost black to various bright variants, often with dark zigzag lines, and triangular irregular light flecks. Operculum is reddish, pseudo-apophysis is absent, while apophysis has a wide platelet part. For more details see Glöer (2019: 41, figs 26, 27). Distribution and ecology. The most widespread among Theodoxus species, this snail is fairly common throughout Europe, and recorded in Asia (Near East) and northern Africa (Bunje 2005; Glöer 2019). It prefers hard substrate of larger rivers in the region (Marković et al. 2014). The most abundant populations in Serbia are found in the large rivers such as the Danube, Sava, and Tisza Rivers. Other remarks. Although being considered of Ponto-Caspian origin (Bunje 2005) nowadays it is regarded as an introduced, or even an invasive taxon, in the Danube basin by some authors (Kebapçý & Van Damme 2012). It has LC status on the IUCN Red List (Seddon & Killeen 2010)., Published as part of Marković, Vanja, Gojšina, Vukašin, Novaković, Boris, Božanić, Milenka, Stojanović, Katarina, Karan-Žnidaršič, Tamara & Živić, Ivana, 2021, The freshwater molluscs of Serbia: Annotated checklist with remarks on distribution and protection status, pp. 1-64 in Zootaxa 5003 (1) on page 9, DOI: 10.11646/zootaxa.5003.1.1, http://zenodo.org/record/5120059, {"references":["Linnaeus, C. (1758) Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Vol. 1. Apud J. B. Delamolliere, Detroit, Lugduni, 220 pp. https: // doi. org / 10.5962 / bhl. title. 542","Matonickin, I., Pavletic, Z., Habdija, I. & Stilinovic, B. (1975) Prilog valorizacije voda ekosistema rijeke Save. Sveucilisna naklada Liber, Zagreb, 95 pp.","Jakovcev-Todorovic, D., Paunovic, M. M., Stojanovic, B., Simic, V. M., Dikanovic, V. & Veljkovic, A. (2005) Observation of the quality of Danube water in the Belgrade region based on benthic animals during periods of high and low water conditions in 2002. Archives of Biological Sciences, 57 (3), 237 - 242. https: // doi. org / 10.2298 / ABS 0503237 J","Paunovic, M., Csanyi, B., Knezevic, S., Simic, V., Nenadic, D., Jakovcev-Todorovic, D., Stojanovic, B. & Cakic, P. (2007 a) Distribution of Asian clams Corbicula fluminea (Muller, 1774) and C. fluminalis (Muller, 1774) in Serbia. Aquatic Invasions, 2 (2), 105 - 112. http: // doi. org / 10.3391 / ai. 2007.2.2.3","Markovic, V., Atanackovic, A., Tubic, B., Vasiljevic, B., Kracun, M., Tomovic, J., Nikolic, V. & Paunovic, M. (2012) Indicative status assessment of the Danube River (Iron Gate sector 849 - 1,077 rkm) based on the aquatic macroinvertebrates. Water Research and Management, 2 (2), 41 - 46.","Martinovic-Vitanovic, V. M., Rakovic, M. J., Popovic, N. Z. & Kalafatic, V. I. (2013) Qualitative study of Mollusca communities in the Serbian Danube stretch (river km 1260 - 863.4). Biologia, 68 (1), 112 - 130. https: // doi. org / 10.2478 / s 11756 - 012 - 0137 - 3","Tomovic, J., Paunovic, M., Atanackovic, A., Markovic, V., Gacic, Z., Csanyi, B. & Simic, V. (2014) Biotic typology of the Dan- ube River based on distribution of mollusc fauna as revealed by the Second Joint Danube Survey (2007). Acta zoologica bulgarica, 66 (4), 527 - 537.","Gloer, P. (2019) The freshwater gastropods of the West-Palaearctis. Biodiversity Research Laboratory, Hetlingen, 399 pp.","Bunje, P. M. (2005) Pan-European phylogeography of the aquatic snail Theodoxus fluviatilis (Gastropoda: Neritidae). Molecular Ecology, 14 (14), 4323 - 4340. https: // doi. org / 10.1111 / j. 1365 - 294 X. 2005.02703. x","Markovic, V., Tomovic, J., Ilic, M., Kracun-Kolarevic, M., Novakovic, B., Paunovic, M. & Nikolic, V. (2014) Distribution of the species of Theodoxus Montfort, 1810 (Gastropoda: Neritidae) in Serbia: an Overview. Acta Zoologica Bulgarica, 66 (4), 477 - 484.","Kebapcy, U. & Van Damme, D. (2012) Theodoxus fluviatilis (errata version published in 2017). The IUCN Red List of Threatened Species, 2012, e. T 165352 A 113400624. [downloaded 24 March 2021] https: // doi. org / 10.2305 / IUCN. UK. 2012 - 1. RLTS. T 165352 A 1081028. en","Seddon, M. B. & Killeen, I. (2010) Theodoxus fluviatilis. The IUCN Red List of Threatened Species, 2010, e. T 165352 A 6005432. [downloaded 3 May 2021]"]}

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 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.

A small collection of molluscs placed in the Regional Museum in Litoměřice (Northern Bohemia) was revised. There are 139 species of molluscs (128 gastropods and 11 bivalves) of 35 families in 612 items. The most important part of the collection includes lots from the period of 1887–1920 by Heinrich Ankert. Some voucher specimens of Theodoxus fluviatilis (1917), being a recently extinct species in the Czech Republic, were found.

Differences in salinity are boundaries that act as barriers for the dispersal of most aquatic organisms. This creates distinctive biota in freshwater and brackish water (mesohaline) environments. To test how saline boundaries influence the diversity and composition of host-associated microbiota, we analyzed the microbiome within the digestive tract of Theodoxus fluviatilis, an organism able to cross the freshwater and mesohaline boundary. Alpha-diversity measures of the microbiome in freshwater and brackish water were not significantly different. However, the composition of the bacterial community within freshwater T. fluviatilis differed significantly compared with mesohaline T. fluviatilis and typical bacteria could be determined for the freshwater and the mesohaline digestive tract microbiome. An artificial increase in salinity surrounding these freshwater snails resulted in a strong change in the bacterial community and typical marine bacteria became more pronounced in the digestive tract microbiome of freshwater T. fluviatilis. However, the composition of the digestive tract microbiome in freshwater snails did not converge to that found within mesohaline snails. Within mesohaline snails, no cardinal change was found after either an increase or decrease in salinity. In all samples, Pseudomonas, Pirellula, Flavobacterium, Limnohabitans, and Acinetobacter were among the most abundant bacteria. These bacterial genera were largely unaffected by changes in environmental conditions. As permanent residents in T. fluviatilis, they may support the digestion of the algal food in the digestive tract. Our results show that freshwater and mesohaline water host-associated microbiomes respond differently to changes in salinity. Therefore, the salinization of coastal freshwater environments due to a rise in sea level can influence the gut microbiome and its functions with currently unknown consequences for, e.g., nutritional physiology of the host. DH, CK, VK, KK, and HT were supported by the European Regional Development Fund/Estonian Research Council funded “Mobilitas Plus Top Researcher grant MOBTT24.” In addition, VK was supported by Estonian Research Council grant PUT1389. The project is also supported by the Baltic-German University Liaison Office and the German Academic Exchange Service (DAAD) with funds from the Foreign Office of the Federal Republic of Germany. Financial support was also provided by the German Research Foundation (DFG), RTG 2010. DH, CK, VK, KK, and HT were supported by the European Regional Development Fund/Estonian Research Council funded “Mobilitas Plus Top Researcher grant MOBTT24.” In addition, VK was supported by Estonian Research Council grant PUT1389. The project is also supported by the Baltic-German University Liaison Office and the German Academic Exchange Service (DAAD) with funds from the Foreign Office of the Federal Republic of Germany. Financial support was also provided by the German Research Foundation (DFG), RTG 2010.

The freshwater snail Theodoxus fluviatilis (Neritidae) is one of the most widely distributed gastropod species of the family Neritidae. The species is particularly sensitive to the quality of its environment, mainly due to its nutrition mode, which makes it a very good bioindicator of freshwater environments. Here, we examine the occurrence of this species in the Upper Rhone river by morphological observations and environmental DNA detection, in order to assess the impact of environmental changes on this particularly sensitive ecosystem. The Upper Rhone has been extremely altered by human activity. The main consequence of these changes has been the disappearance of species and the drying up of secondary streams (floodplain) connected to the Rhône. To restore the Rhône's biodiversity and hydraulic profile, an environmental and hydraulic restoration program was initiated, since the 1990s, on the Upper Rhône by the Compagnie National du Rhône (CNR). After restoration, Theodoxus fluviatilis was observed in large quantities in the wildlife surveys and was considered as a positive witness of changes introduced by restoration. Unfortunately, recently Theodoxus fluviatilis has disappeared from the sites where it was previously present in large quantities, possibly due to the effect of periodic emptying of Verbois dam that flushed the sediments down the river. Environmental DNA (eDNA) detection is a non‐invasive technique that can provide reliable information about a macrobial species occurrence based on intra- and extracellular material shed by an organism into the environment. Here, we developed a non-invasive quantitative PCR (qPCR) approach to detect Theodoxus fluviatilis in eDNA from water and sediment samples. First, we collected different individuals of Theodoxus fluviatilis from three different populations to obtain reference DNA sequences and create specific primers and probe for qPCR. After extensively testing the specificity and sensitivity of our method, we used this approach on thirty replicates from ten sites. We obtained positive eDNA detection for sites where the species was present in morphotaxonomic biodiversity surveys, and no detection at sites where the species was not found by morphological approach. The match between both approaches confirmed that the eDNA detection method provides a congruent presence/absence response, and that the future use of this method for quantitative assessment of Theodoxus fluviatilis in freshwater is promising.

The phenomenon of Theodoxus fluviatilis presence in freshwater and marine habitats for a possible use of the species as a bioindicator is considered. The information about finding of T. fluviatilis in the basins of the Black, Baltic and North Seas is analyzed, and the possibility of the use of laboratory experiments, connected with the adaptive ability of the species to different salinity, is critically examined. Materials of the drilling in Sevastopol Bay are examined, and the results are compared with the published data on chorology and ecology of the species. The presence of T. fluviatilis in Holocene marine sediments of the Bay and in the contemporary brackish-water environment is explained by the mollusk localization near the sources of the submarine groundwater discharge. The following conclusion is drawn: T. fluviatilis can be used as an indicator species in freshwater or in low brackish (up to 5 ‰) water environment.

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.

Crabs are some of the most successful introduced species among marine organisms, and they can be an important structuring force in marine communities. Recently, the North American white-fingered mud crab, Rhithropanopeus harrisii, has invaded the Northern Baltic Sea. This is an area where no native crab species exist, and the addition of a novel functional species to the low species diversity of the Baltic Sea could have large community-level impacts i.e. modifying biotic interactions and/or altering ecosystem functioning. We examined the predatory behavior of introduced R. harrisii both in the laboratory and field focusing in shallow, hard bottom habitats dominated by the alga Fucus vesiculosus. In the laboratory environment, R. harrisii was an effective predator of littoral grazers, readily consuming both sessile fauna (Mytilus trossulus) and also mobile species such as isopods (Idotea balthica) and gammarid amphipods (Gammarus sp.). When studying the predation of different sized prey items, R. harrisii preyed upon small and medium sized prey of both mobile and sessile species. However, in the field experiment with the native faunal community associated with F. vesiculosus, R. harrisii negatively impacted only the abundance of the snail Theodoxus fluviatilis, possibly through indirect effects. Nevertheless, R. harrisii significantly decreased both the prey species richness and diversity but not the total number of potential prey individuals associated with F. vesiculosus. In conclusion, predatory behavior of this novel crab has the potential to impact the native macroinvertebrate littoral community, but the realized predation pressure in the field is lower than could be expected from laboratory experiments.

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.

The river nerite ( Theodoxus fluviatilis , Linnaeus, 1758 ) is one of the most common gastropod grazer species in Europe inland and brackish waters. Its feeding activity significantly impacts on periphyton which has a decisive role on the water parameters and the population dynamics. In the present study, reproductive outputs and larval phases of the river nerites were examined via field collected and laboratory cultivated samplings. The length of capsules laid by adults was between 0.7 and 1.1 mm. Viable embryos were detected first on the 33 rd day post-spawning. After few development phases embryo reached a ready-to-hatch phase with completely developed foot and pigmented protoconch before hatching. There was never more than one embryo per capsule. The earliest hatching was observed on the 53 rd day of spawning. But most of the embryos did not hatch even they were fully developed. The shell length of the hatchlings was about 0.8 and the width was 0.6 mm. It was estimated that the length of a newly hatched crawling juvenile can be about 1/7 of the length of an adult.

The endangered freshwater snail Theodoxus fluviatilis is a widely distributed European member of the gastropod family Neritidae. This taxon was abundantly found in the River Rhine until the end of the 20th century, and was considered to be extinct there since the late 1990s. Since 2006, a new, but morphological different form of T. fluviatilis has been recorded in the Upper Rhine region. Our aim was to identify the source of the recent populations by analysing individuals from five sites throughout the current known distribution along the River Rhine. Therefore, we sequenced the mitochondrial cytochrome c oxidase subunit I (COI) gene, and compared the data with those from individuals collected in the early 1990s and 40 already known haplotypes from a pan-European study. Our results show that all studied recent Rhine individuals harbour only one COI haplotype that corresponds to an already known haplotype described from the River Danube and the Ukraine region near the Black Sea. This suggests that a re-colonisation of the River Rhine by T. fluviatilis from the River Danube is the most likely scenario of the re-establishment of the species. This route of invasion is known for other freshwater taxa that originate from the Ponto-Caspian region. Even though the current Rhine populations belong to T. fluviatilis their invasion may have consequences for the native Central European populations. Therefore, we recommend considering the current Rhine population as ‘cryptic invader’.

According to stoichiometric principles, the ratios at which consumers recycle nutrients depend on the elemental compositions of the consumer and its food. However, nutrient assimilation efficiencies and ingestion rates can vary among consumer species and, thus, can affect the rates of consumer-mediated nutrient recycling (CNR). The grazer Theodoxus fluviatilis has high nutrient excretion rates of either P or N, depending on grazer growth limitation, and has a high body N. I examined how a grazer with a high proportion of N in its body tissues can assimilate enough N to maintain that N content despite high N excretion rates by estimating the mass balance for nutrient recycling including nutrient excretion through fecal pellets. I used the snail species Theodoxus fluviatilis and Lymnea peregra fed nutrient-enriched periphyton in a 2-d grazing experiment done in 48 experimental units. I estimated periphyton and grazer nutrient stoichiometry and nutrient excretion rates and ratios in dissolved and fecal-pellet form, and calculated nutrient assimilation efficiencies of the limiting nutrient (N). Theodoxus fluviatilis had higher N excretion rates, lower N assimilation efficiency, and higher ingestion rates than L. peregra. Thus, T. fluviatilis recycled more N by ingesting and processing a larger amount of food per unit time than L. peregra. My study shows that grazers with low nutrient assimilation efficiencies and high nutrient demands can assimilate sufficient nutrients via high ingestion rates. The consequence of this strategy (high ingestion and excretion rates) could be a more rapid nutrient turnover in ecosystems dominated by these grazers.

This study of periphytic algae and gastropods differentiation on macrophytes, stones, and dam substrates and the relationships between these communities in the vegetative season of 2001-2003 was conducted in the vicinity of a hydroelectric plant on the Pasłeka River. Damming the river caused decreased water discharge upstream from the plant, and increased it downstream. Thus, oxygen conditions downstream from the plant improved, but high nutrient concentrations were also recorded. Generally, increased orthophosphate concentrations do not allow river waters to be classified as having good or maximum ecological potential. Damming contributed to changes in the growth conditions of the periphytic algae and gastropods and their differentiation. The highest biomass of periphytic algae was noted on the dam, while the highest gastropods biomass was noted on macrophytes. The periphytic algae was dominated by the diatoms Diatoma vulgaris and Melosira varians (epiphyton, dam) and the chlorophytes Ulothrix tenuissima and Spirogyra sp. (epilithon), while the gastropods were dominated by Lymnea stagnalis (macrophytes), Theodoxus fluviatilis (stones), and Radix balthica (dam). The relationship between the gastropods and the periphytic algae on macrophytes and the dam in spring and summer revealed an increase in gastropods biomass and a decrease in periphytic algae biomass. This was indicated by the negative correlation between the biomass of these communities.

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.

The periphyton of stony hard substrates in the littoral zone of lakes is inhabited by an abundant and diverse algae and meiofauna assemblage that is regulated by grazing. The objective of our study was to examine the effect of macroinvertebrate grazers on periphytic algae and meiofaunal organisms at different depths in the littoral zone of Lake Erken (Sweden). To this end, a 2-factorial field experiment was carried out in which macrofaunal access to the periphyton was manipulated at 3 different water depths (30, 70, and 200 cm). Grazing effects on algal biomass varied among depths and were highest in both deeper zones. Compared to algal biomass, the abundance of meiofaunal organisms was less affected by grazing because macrograzers significantly reduced meiofauna only at the 200-cm depth. The organism mainly responsible for the depth-dependent differences in grazer effects was the snail Theodoxus fluviatilis, which dominated macrofaunal assemblage at depths where grazing effects were the strongest (70 and 200 cm). The abundance of T. fluviatilis was positively correlated with the proportions of reduced algal biomass and reduced meiofaunal abundance. Meiofaunal groups and individual nematode species responded differently to grazing, so our results further revealed that grazing macroinvertebrates affected the composition of the meiofaunal assemblage. However, meiofaunal and nematode assemblages differed more across depths than across grazing treatments, suggesting that other depth-related factors (e.g., hydrodynamics or light) also were important for structuring periphytic meiofaunal assemblages.

Biocide-based antifouling (AF) paints are the most common method for preventing biofouling, i.e. the growth of algae, barnacles and other organisms on boat hulls. AF paints for leisure boats are predominantly based on copper (Cu) as the main biocide, with zinc (Zn) present as a pigment and stabilizer. Both metals are released from the paint matrix into the water column, leading to contamination of marinas which typically have only limited water exchange. Thus, the aim of this PhD thesis was to describe the use of AF paints in different regions in Sweden, as well as the associated environmental consequences with regard to contamination of the environment and toxicity to non-target aquatic snails. Using a recently developed X-ray fluorescence application, high levels of Cu were detected on boats moored in freshwaters, despite a more than 20-year-old ban, as well as high levels of tin (Sn) on 10 % of the boats, indicating the presence of (old) tributyltin paints (TBT), which might pose an environmental risk and a health hazard for people performing the paint scraping (paper 1). In addition, very high levels of Cu and Zn were measured in the biofouling material collected from the boat hulls, and this is problematic because the biofouling is commonly disposed of on the soil in boatyards at the end of each season. No difference was found in the amount of biofouling on boats coated with Cu or biocide-free paints, which implies that Cu might be currently overused in areas of low salinity and low barnacle density (paper 2). This work also introduces the use of a new species for ecotoxicological field experiments, the snail Theodoxus fluviatilis. Chronic field experiments (paper 3) revealed 6-fold increases in snail mortality, negative growth and up to 67-fold decreased reproduction in marinas, compared to areas not impacted by boating (‘reference areas’). Moreover, a higher prevalence of snails with histopathological alterations (e.g. necrosis of gills, gonads, midgut gland and parasite infestation, among others) was observed in the marinas, compared to the reference areas (paper 4). Statistical modelling indicated that the majority of the toxic effects were best predicted by the metals, most likely originating from AF paints. The results presented in this thesis depict some important aspects of AF paint use in brackish water and highlight the necessity of implementing a suitable management practice for the heavily contaminated biofouling waste in order to minimize the risk to soils. In addition, the evidence of toxicity to snails in marinas can be used as a basis to increase the public understanding of the impact of recreational boating and encourage people to choose less toxic alternatives to AF paints. At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

First detailed limnological study was performed from April 2003 to June 2008 in a 396.6 km long section of the Serbian Danube (divided in three parts; from 1260 r-km to 863.4 r-km) to examine community composition and spatial distribution of Mollusca with special attention to the expansion of Ponto-Caspian species, propagation of invasive and introduced species and occurrence of endemic species. Mollusca samples were collected at 15 sites in April, June, September and November. We investigated the spatial distributions and calculated the faunistic similarity of localities with respect to the community composition using the Sorensen Quotient of Similarity. Site variation in analyzed qualitative traits was examined using correspondence analysis. Additionally, the obtained Complete Linkage City-block (Manhattan) distances among sites/parts were subjected to UPGMA (unweighted pair-group method using arithmetic averages) cluster analysis. The class Gastropoda was represented by 18 species from two subclasses (Prosobranchia — six families and Pulmonata — three families).The class Bivalvia was represented by 15 species from four families of order Eulamellibranchiata. Mollusca were represented by 33 species belonging to 17 genera and 13 families. Out of five recorded Ponto-Caspian species in the studied Danube stretch, Lithoglyphus naticoides (Pfeiffer, 1828) and Dreissena polymorpha (Pallas, 1771) are assumed to be invasive species with the highest occurrence frequency (F = 1, each). Four new species in invertebrate fauna for the Danube, denoted as the introduced species — Neozoa, were identified: Theodoxus fluviatilis (L., 1758), Corbicula fluminalis (Muller, 1774), C. fluminea (Muller, 1774), and Sinanodonta woodiana (Lea, 1834). The only endemic species of Gastropoda found in the Danube was Viviparus acerosus Bourguignat, 1862.

Abundant wood remains and buried trees have been found in the western part of Lithuania near Zakeliškiai and Lyduvėnai on Dubysa River (a tributary of Nemunas River) where deposits are rich in organic remnants and buried soils. In Zakeliškiai and Skiručiai sections of Dubysa River oxbow sediments were investigated by various methods (dendrochronological, carbonate, granulometric, pollen and mollusc fauna analysis). In addition, these sections were dated using the radiocarbon method. Samples were collected from deposits of Dubysa River outcrops. The studied oxbow lakes have existed for more than 5 thousand years (from ca. 4300 BC to 1000 AD). During this period organic rich deposits with trees and branches were formed in the oxbow lake. This indicates that at the end of Atlantic, during Subboreal and in the early Subatlantic periods there was a forest growing that contained mainly oaks which were falling down into an oxbow lake and later were covered by sandy and silty deposits. The granulometry of alluvial deposits, as well as the mixture of medium-grained sand and silt show different stages of Dubysa River palaeochannel formation: riverbed and oxbow lakes. Three climate warming cycles were revealed according to carbonate analysis data in all investigated sections. The rheophile thermophilous Holocene age molluscs species Bithynia tentaculata L., Unio cf. crassus Philipsson, Pisidium amnicum (Müller), Theodoxus fluviatilis (Linnaeus) have been found. The pollen composition and sequences have been divided into five local pollen assemblage zones (LPAZ) and described according to pollen spectra in each zone. In this way it is possible restore palaeoclimatic coherent evolution, trends and cyclical change.

Periphyton harbours a complex microbial food web with different trophic levels, but little is known about trophic interactions within this food web and its response to factors that potentially control the entire community. We used natural periphyton communities from Lake Erken (Sweden) in 2 experiments manipulating grazer presence. In addition to an ungrazed control, we included natural densities of either of 2 snail species (Theodoxus fluviatilis and Bithynia tentaculata) in order to test how generalist consumers affect different components of the periphyton. In the second experiment, we additionally manipulated light supply to alter the heterotroph-autotroph ratio in the periphyton and thus potentially the trophic interactions. In both experiments, grazer presence decreased algal biomass immediately and shifted the community composition from dominance of large filamentous forms to dominance of prostrate and motile unicellular species. Biomass of bacteria, heterotrophic nanoflagellates, ciliates and meiofauna also decreased with grazing, but with differentiated temporal dynamics and effect strength. In the ungrazed control, first heterotrophic protists and later meiofaunal biomass increased, indicating strong bottom-up and top-down propagation of trophic interactions in the microbial food web. High light increased the biomass of mixotrophic ciliates and nanoautotrophs but not total algal biomass. Grazer presence decreased algal richness in the second experiment, but increased evenness of the algal community under high light conditions. We conclude that grazer presence puts different pressure on the components of the periphyton, which are further linked by direct or indirect internal trophic processes.

This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants of the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.

During the 1980s, Chelicorophium curvispinum and Dikerogammarus villosus colonized the lakes of the IJsselmeer area in The Netherlands. With the arrival of C. curvispinum the indigenous Apocorophium lacustre retreated to a small, sheltered bay with particular microconditions. The arrival of D. villosus is probably linked to a decrease of Gammarus tigrinus and possibly the disappearance of the gastropod Theodoxus fluviatilis. However, the occurrence of D. villosus may be restricted to stones along the banks of the lakes, and even there, G. tigrinus seems to remain stable at lower population densities. In samples from the beds of Dreissena polymorpha on the bottom of the lakes, D. villosus was virtually absent and densities of C. curvispinum were relatively low. G. tigrinus was here the single gammaridean species. Other changes in densities of invertebrates, like strong decreases in densities of Tricladida, Hirudinea, Asellidae, D. polymorpha and several gastropods, differ in details of timing from the arrival of the invaders, and are at least partly linked to other factors. In the River IJssel, the main source of invaders to the lakes, similar decreases in species abundance followed exceptionally high discharge events, but preceded both a relatively strong decrease of chlorophyll a levels and the arrival of D. villosus. This suggests that this arrival was not a direct cause of the recorded declines, although it may have prevented recovery.

Coastal eutrophication has resulted in the reduced abundance of the perennial macroalga Fucus vesiculosus L. due to negative effects of increased turbidity, spatial competition, and grazing. We conducted a factorial field experiment to explore the main and interactive effects of three factors on the recruitment success of F. vesiculosus. We manipulated (1) substrate occupancy by offering unoccupied substrates and substrates occupied by a natural assembly of macroalgal spores, periphyton and loose material, (2) nutrient availability by exposing substrates to ambient and enriched nutrient conditions, and (3) herbivory by exclosing the natural herbivore community and enclosing either small (Hydrobia spp.) or large (Theodoxus fluviatilis L.) snails. Microrecruit density of F. vesiculosus depended on the density of parent algae in ambient nutrient availability, whereas, under enriched conditions, such dependency disappeared. Microrecruit density was lower on previously occupied than on unoccupied substrates and at enriched rather than ambient nutrient levels. The lowest recruitment success resulted from a combination of these two treatment levels. The microrecruit density of F. vesiculosus decreased sharply with the density of filamentous algae indicating that competition with opportunistic species contributed to poor recruitment success. Microrecruit density did not differ between the grazer exclosure and the natural grazer community treatment level reflecting locally low grazer densities and consequent weak grazing pressure in the study site. However, the enclosure of snails at higher densities that still naturally occur in the nearby areas affected the recruitment success of F. vesiculosus. This effect was dependent on nutrient availability; at ambient levels, snail grazers had only a minor negative effect on microrecruit density whereas under enriched conditions, both snail species negatively affected recruitment success. Thus, instead of reducing competition and thereby benefiting the perennial slow-growing F. vesiculosus, negative grazing effects by both snail species increased under nutrient-enriched conditions.

Grazing pressure on macroalgae in littoral communities may vary with algal species, the age of an algal individual and grazer identity. Previous studies on alga–grazer interactions have shown that grazer preference for an algal species may release another one from interspecific competition. We measured the impacts of four common grazer taxa and the natural grazer guild on macroalgal communities at both their colonization and adult stages, and compared the impacts to grazer exclosures. The grazer effects were stronger on colonizing than on adult macroalgae; grazers did not reduce the total density of adult algae. Grazers both feed on propagules and indirectly facilitate other algae, depending on the grazer or algal species. Hydrobia species increased the settlement of spores of the red alga Ceramium tenuicorne. Similarly, the gastropod Theodoxus fluviatilis tended to facilitate one crustose algal species, but decreased the propagule density of annual filamentous algae, suggesting a preference for one species to the advantage of another. Effects of crustacean mesograzers on the studied macroalgae were weak. These results indicate that northern Baltic macroalgae are limited to grazing mainly during their colonization stage.

Summary 1. We aimed to separate the effects of grazers on periphyton via grazing from that of nutrient recycling from their faecal pellets. 2. We set up three different experimental treatments (snails/no snails/faecal pellets) and sampled over 16 days. The ‘snail’ treatment contained a low density (snail biomass c. 14 g−2) of the gastropod grazer Theodoxus fluviatilis and the ‘faecal pellet’ treatment received the same amount of faecal pellets as were produced in the ‘snail’ treatment. Whereas the ‘faecal pellet’ treatment provided extra nutrients to periphyton from the faeces, the ‘snail’ treatment provided nutrients in the form of both faeces and in excreta. There was also direct grazing on periphyton in the ‘snail’ treatment. The ‘no snail’ was not grazed and received no nutrients in faeces or excreta. 3. We measured periphyton C, N and P content, chlorophyll-a (chl-a), primary production, bacterial biomass, bacterial production and bacterial respiratory activity. In the water column we measured dissolved inorganic N and soluble reactive P. 4. Snails increased the amount of dissolved inorganic N in the water. On day 16, the periphyton N : P ratio in the ‘faecal pellet’ treatment was lower, and periphyton P content was higher, than in the other two treatments. N : P ratios decreased over time in the ‘faecal pellet’ treatment. Primary and bacterial production were positively correlated in all treatments. 5. Algal chl-a and primary production of periphyton per unit area and periphyton chl-a : C ratios increased over the 16 day in the ‘snail’ treatment, and thus excretion of dissolved N by snails had a stronger positive effect on the periphyton community than N and P in faecal pellets. 6. Our data show that excretion and egestion can have different effects on periphyton, probably because of the higher proportion of dissolved N in excreta and the higher proportion of P recycled in faecal pellets. The relative effect of nutrients recycled in egesta or in excretions, probably depends on the form of nutrient limitation of the periphyton. Further, the different components of the periphyton matrix could react differently to the different forms of nutrient recycling. 7. We conclude that direct grazing effects are less important than nutrient effects when nutrients are limiting and grazing pressure is low. Further, the spatial separation of different grazing effects can lead to differences in periphyton production and nutrient stoichiometry. This might be an explanation for the patchiness of periphyton in nature.

The European water framework directive (WFD) aims at achieving good ecological status of water bodies, which implies assessment of their current ecological quality status in respect to defined reference (pristine) conditions. In this paper, two historical biodiversity datasets (from 1920s and 1950s) and results from the recent inventory are used to trace the long-term changes of the macrozoobenthos in the eutrophic boreal lagoon of the Baltic Sea. In comparison of datasets the highest congruence was obtained for molluscs and malacostracan crustaceans, which also had a similar level of taxonomic emphasis between studies. Considering inconsistencies in methodology and taxonomic determination, only few species extinctions in these groups did likely occur during the last 100 years. Two amphipod species (Gammarus pulex and Gammarus lacustris) were not found during the recent survey, whereas five new species of this taxonomic group occurred in the lagoon since 1950s. The causes of these extinctions remain unclear; however displacement by established new amphipods cannot be excluded. Theodoxus fluviatilis was recently recorded in the very restricted area of the lagoon, while in earlier studies the species was mentioned as common and widely distributed in the water body. On the other hand, 10 gastropod species and 9 bivalves were reported for the first time in the lagoon and most likely have been overlooked in earlier surveys. Approximately 10% of the species have their origin outside the Baltic Sea basin and the number of invasions considerably exceeds the number of likely extinctions. Assessment scheme of such changes is unclear following WFD guidelines, therefore elaboration of a framework for evaluation of the alien species diversity in a context of local biodiversity should attain more effort when implementing the WFD.

1.A study on the distribution pattern and conservation of freshwater molluscs of the south Guadiana River (SW Iberian Peninsula) was carried out between the Alqueva dam and the Atlantic Ocean. 2.The knowledge of the distribution and abundance of molluscs before the closure of the Alqueva dam is an important tool for evaluating the potential reduction in diversity and the changes in species conservation status that may occur later. 3.Twenty-three species (15 gastropods and 8 bivalves) were found in the study area. The presence of Unio crassus and Potomida littoralis indicates the importance of this basin for the conservation of endangered mussels (Unionidae) in the south Iberian Peninsula. 4.Drainage area above the sampling site explained almost 58% of the variation in species richness. Larger drainage areas had a higher number of species, including those endemic to the basin. 5.Patterns of habitat use were examined to identify species preferences with respect to the erosional-depositional gradient. Islamia minuta, Pisidium casertanum and Pisidium personatum find their optimum habitat in headwaters, whereas Theodoxus fluviatilis, Mercuria emiliana, Radix auricularia and all unionid species inhabit large and stable habitats downstream without marine influence. 6.Populations of invasive Corbicula fluminea were found in the Guadiana River basin, both in rivers with large drainage areas and in brackish waters near the mouths of rivers. Copyright © 2006 John Wiley & Sons, Ltd.

A population of Theodoxus fluviatilis L in the littoral zone of Lake Esrom was investigated from November 1977 to February 1979. The population was sampled every month in the winter period and twice during the rest of the year. Biomass was estimated as ash-free dry weight (AFDW) of the organic matter both of the soft parts of the animal and the shell itself. The relation between AFDW ( c ) and shell length ( l ) was log c =2.9509×log ( l )−1.7120. The population comprised more than 1 year-class, which could be separated by shell length, by a narrow band on the shells and the growth of algae on the shell. The life cycle lasted 2 1 2 - 3 years. The oldest animals had a shell length of 7.0–7.5 mm. A few individuals who were estimated to be 3 1 2 years had a shell length up to 8.6 mm. Population density varied between 575 and 2115 individuals m −2 on the stony substratum. The average was 1160 individuals m −2 . Mortality was low during the summer period. In winter many animals died due to the effect of ice and stormy weather on the stony substratum. Growth of the animals was estimated from the shell length. Maximum growth was observed from May to August with no growth during the winter. Egg capsules were found on the stones all year round. New capsules were found from late May to the middle of November. Most freshly laid capsules were observed in May–June and August–September. Capsules from the late summer hatched in spring and capsules laid in the spring hatched in August–September. The average annual net production for the whole population was estimated by three methods. The Allen curve method gave 1.895 AFDW m −2 , the growth-increment method gave 1.784 mg AFDW m −2 and the Hynes method 2.284 mg AFDW m −2 . Corresponding estimated P/B ratios were 1.29, 1.30 and 1.57. Annual net-production of the four investigated year-classes was 16 mg AFDW m −2 year −1 for 1975, 224 mg AFDW m −2 year −1 for 1976, 1.258 mg AFDW m −2 year −1 for 1977 and 287 mg AFDW m −2 year −1 for 1978. P/B ratios for the three oldest year-classes were, respectively, 0.32, 0.50 and 1.67. A comparison with other investigations on gastropod life cycles, reproduction and P/B ratios is made and differences discussed. Variations are correlated to temperature, and food quality and quantity.

Investigating the geographical distribution of genetic lineages within species is critical to our understanding of how species evolve. As many species inhabit large and complex ranges, it is important that phylogeographical research take into account the entire range of widespread species to clarify how myriad extrinsic variables have affected their evolutionary history. Using phylogenetic, nested clade, and mismatch distribution analyses on a portion of the mitochondrial COI gene, I demonstrate that the wide-ranging freshwater snail Theodoxus fluviatilis possesses in parallel many of the phylogeographical patterns seen in less widespread freshwater species of Europe. Fragmentary forces play a major part in structuring the range of this species, with 12 of 14 geographically structured nested clades displaying a distribution consistent with fragmentation or restricted dispersal. Certain regions of southern Europe harbour the majority of genetic diversity (total haplotype diversity, H = 0.87), particularly Italy (H = 0.87) and areas surrounding the Black Sea (H = 0.81). Post-Pleistocene range expansion is pronounced, with the majority of northern European populations (95% of sample sites) having arisen from northern Italian individuals that initially colonized northern Germany. Additionally, two highly divergent haplotype lineages present in northern Germany imply that there were at least two postglacial recolonization routes. Estuaries may also provide a means of dispersal given that no genetic differentiation was found between estuarine populations and neighbouring freshwater populations. Taken together, these data reveal a species with a complex genetic history resulting from the fragmentary effects of European geology as well as continuous and discrete range expansion related to their aquatic biology.

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‰).

Increase of phenolic secondary metabolites, phlorotannins, in brown algae due to gastropod grazing has been interpreted as an anti-herbivore adaptation. Here we tested whether such a response could be due to changes in truly available resources for the alga, not by the grazing activity of snails as such. We allowed two species of snails, Theodoxus fluviatilis and Physa fontinalis to graze on Fucus vesiculosus. These species feed on epibiota and particulate matter on the thallus but do not eat the thallus of F. vesiculosus. We further simulated snail grazing by nutrient enhancement, removal of epibiota and by a combination of the two. Manipulations of nutrient and light availability revealed the crucial role of epibiota in mediating resource availability for F. vesiculosus. Nutrient enhancement alone increased epibiota and decreased phlorotannins. Cleaning the thallus resulted in increased growth, and together with nutrient enhancement also in a trade-off with phlorotannins. Presence of T. fluviatilis on the thallus induced phlorotannin production, a response differing from the simulations of snail grazing. However, we suggest that the increase in phlorotannins may not be an induced defense but rather a consequence of a specific way of resource manipulation by this snail species. T. fluviatilis removes hyaline hairs that facilitate nutrient uptake. P. fontinalis did not remove hyaline hairs and the response of the alga to its grazing was similar to the treatment where we mechanically removed epibiota suggesting that cleaning of the thallus is the major mechanism how this snail species affects F. vesiculosus. Genetic variation in phlorotannin concentrations highly exceeded the induced responses of simulated or real snail grazing. This casts doubt for the efficiency of induced phlorotannin production to act as a defense, but is not contradictory with the interpretation of phlorotannins responding to variation in resource availability.