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The ongoing intensification of the hydrological cycle calls for the identification and assessment of factors controlling catchment resilience to climate change. Stable isotopes of O and H in streams and precipitation are cardinal tools in this respect – notably for investigating questions related to water source, flowpaths and transit times. However, the spatial and temporal variability of these tracers remain largely unknown – essentially due to the limited availability of long historical time series of O-H isotope signatures in stream water, as opposed to the multi-decadal records in precipitation of the IAEA’s GNIP database (https://www.iaea.org/services/networks/gnip). Based on their quality as natural archives of in-stream environmental conditions, freshwater mussels have been recently used for complementing stream water δ18O isotope records. With an average life span of ca. 10 years (up to 200 years for the freshwater pearl mussel), their potential is significant, considering the fact that nearly 1200 freshwater bivalve species inhabit a large variety of river systems and lakes around the globe (Pfister et al., 2018). Our proof-of-concept work has shown that δ18O values extracted from their shells closely mirror the variance of the measured stream water δ18O – both showing a strong damping of the precipitation signal. In our follow-up study, we leverage prior work by Schöne et al. (2020) on potential links between the NAO index, precipitation isotope signatures and subsequent interdecadal variabilities in reconstructed stream water δ18O signals for three catchments located in Sweden. Using freshwater bivalve shell δ18O as a proxy of stream water δ18O signatures, we hypothesize that interdecadal shifts in atmospheric circulation patterns translate into modifications of δ18O isotope signatures in precipitation and subsequent stream water δ18O signals – the latter potentially revealing changes in young stream water fractions related to fast flow paths. In parallel, we stipulate that the long-term δ18O signal in precipitation can be retrieved from historic records and reanalysis data of climate variables, as well as from synoptic atmospheric circulation classifications. Here we focus on findings gained from a unique dataset of 5 years-worth of sub-daily precipitation O-H isotope data from the Belvaux (L) meteorological station, comprising 1443 rainfall samples. We investigated the links between local climate variables, the rainfall amount, atmospheric circulation patterns, and the precipitation δ18O signal. Our results show (i) an anticipated strong temperature-induced seasonality of the δ18O signal, characteristic for semi-continental sites, (ii) a weak but significant amount effect, (iii) a circulation type-dependant influence of local climate variables on the δ18O signal, and (iv) a high variability at the event-scale – indicating the influence of complex frontal systems and moisture recycling. We leveraged these findings for building a multiple linear regression model, explaining up to 50 percent of the variability of the δ18O signal at sub-daily resolution and closely matching the isotopic signal when applying moving averages over periods within a monthly range.

Europe has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other groups remain largely off the public and scientific radar. Freshwater mussels (Bivalvia, Unionida) are an alarming example of this conservation bias and here we point out six conceptual areas that need immediate and long-term attention: knowledge, threats, socioeconomics, conservation, governance and education. The proposed roadmap aims to advance research, policy and education by identifying the most pressing priorities for the short- and long-term conservation of freshwater mussels across Europe., COST - European Cooperation in Science and Technology(CA18239)

A sample of 30 thick-shelled river musselsUnio crassusPhilipsson (Unionida: Unionidae) was collected from the River Sauer in Luxembourg to acquire data on parasitic infestations of the mussels. Among other parasites, different development stages of freshwater mites were collected from the gills and the mantle of the mussels and were documented with bright-field, stereo, and confocal laser scanning microscopy and microscopic X-ray computed tomography. The retrieved data allowed a morphological description of larvae and female adults of the mites and assigning them to the genusUnionicolaHaldeman (Trombidiformes: Unionicolidae) and the subgenusPentataxThor. Additionally, adult stages and larvae were barcoded by sequencing a section of the mitochondrialCOIand18SrRNA genes. This resulted in 4 new, similarUnionicolalineages from the adult stages, which differ in at least 14.7% (uncorrectedpdistance) from those already published. Barcoding of larval DNA was not successful. The comparison with known European species of the genusUnionicolaand analysis of the barcoding results allowed the proposal of a new species of the genusUnionicola.The species was namedUnionicola sauerensissp. nov. after the River Sauer in Luxembourg, where the infested mussels were collected.

The data that supports the findings of this study are available in the supplementary material of this article., Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists., This publication is based upon work from COST Action CA18239, supported by COST (European Cooperation in Science and Technology). A.M.L. was financed by the Institute of Environmental Sciences Jagiellonian University (N18/DBS/000003) and K.N. by the Aragón Government. The authors acknowledge Jarosław Andrzejewski, Bartosz Czader, Anna Fica, Marcin Horbacz, Tomasz Jonderko, Steinar Kålås, Tomasz Kapela, Bjørn Mejdell Larsen, Maciej Pabijan, Katarzyna Pawlik, Ilona Popławska, Joanna Przybylska, Tomasz Przybył, Mateusz Rybak, Kjell Sandaas, Jarosław Słowikowski, Tomasz Szczasny, Michał Zawadzki and Paweł Zowada for providing detailed information on specific examples concerning freshwater mussels in anthropogenic habitats. We thank the editor and two anonymous referees for the valuable suggestions made, which increased the clarity of our manuscript.

Freshwater mussels of the Order Unionida provide important ecosystem functions and services, yet many of their populations are in decline. We comprehensively review the status of the 16 currently recognized species in Europe, collating for the first time their life-history traits, distribution, conservation status, habitat preferences, and main threats in order to suggest future management actions. In northern, central, and eastern Europe, a relatively homogeneous species composition is found in most basins. In southern Europe, despite the lower species richness, spatially restricted species make these basins a high conservation priority. Information on freshwater mussels in Europe is unevenly distributed with considerable differences in data quality and quantity among countries and species. To make conservation more effective in the future, we suggest greater international cooperation using standardized protocols and methods to monitor and manage European freshwater mussel diversity. Such an approach will not only help conserve this vulnerable group but also, through the protection of these important organisms, will offer wider benefits to freshwater ecosystems.

The freshwater pearl mussel (Margaritifera margaritifera) is a highly specialized and sensitive freshwater bivalve, whose survival in the juvenile phase is indicative of high quality habitats. This contribution investigates the use of juvenile freshwater pearl mussels as bioindicators, considering the influence of mussel stock and study stream conditions on juvenile performance, as described by survival and growth rates. A standardized cross experiment was carried out investigating juvenile performance in four different pearl mussel stocks originating from the Rhine, Danube and Elbe drainages, representing distinct genetic conservation units. The juveniles were exposed in five study streams which were selected to integrate pearl mussel streams with different water qualities and recruitment status of the mussel population. Per study stream, five standard mesh cages containing an equal number of 20 (10 × 2) juvenile pearl mussels per stock in separate chambers were installed. Survival and growth rates of juveniles were checked after three months (i.e. before their first winter) and after nine months (i.e. after their first winter). Mussel stock and study stream conditions significantly influenced juvenile performance. Growth rates were determined by study stream conditions and increased with stream water temperature, organic carbon and C/N ratios. Survival rates varied stock-specifically, indicating different levels of local adaptation to their native streams. Due to the detection of stream-specific differences in juvenile performance, freshwater pearl mussels appear suitable as bioindicators. However, a careful consideration of stock-specificity is necessary to avoid false interpretation of bioindication results. The comparison of stock-specific survival in native versus non-native streams implicates that exposure of juveniles outside their native habitats is able to increase breeding success or else serve for risk spreading in breeding programs.

Freshwater pearl mussel (Margaritifera margaritifera L.) is an endangered species. Rearing in captivity for eventual release is one possible method of increasing the likelihood of persistence in different rivers. As rearing is a time-consuming procedure, knowledge about conditions that increase survival and growth rates and decrease the period of the parasitic stage would be advantageous. Experiments with two excystment periods (one preterm in January, induced by artificially raising the water temperature, and a natural one in May) were performed, and the growth and survival rates of juvenile mussels were determined. Furthermore, meristic parameters of the host fish (brown trout, Salmo trutta) infested with glochidia in August the year before were investigated before and after both juvenile collection periods. In January the mean intensity was 151.5 glochidia per fish (±260.6) and 80% of host fish were infested. In May, the mean intensity was 142.7 glochidia per fish (±177.0) with 30% of fish infested with glochidia. Although the condition factors of the fish decreased during the experiments to 0.8 ± 0.1 (January) and 0.7 ± 0.2 (May), no apparent influence on the growth or survival rate of the juvenile mussels was obvious. The output of juvenile mussels was higher in the January excystment period (2854 compared with 2310). During both excystment periods, the length of the freshly excysted juveniles increased slightly from the first to the last day of collection. Mussels excysted with a mean length of 0.32–0.33 mm (at the beginning of the excystment period) and 0.38 mm (at the end). Individuals collected after the first few days of the January excystment period were the most suitable for culture. Growth up to a minimum of 1 mm in 110 days and a survival rate of 62–98% were observed. Juvenile survival from the May excystment period was lower (7–38%) presumably owing to poor water quality in the river. Copyright © 2014 John Wiley & Sons, Ltd.

The last remaining population of Margaritifera margaritifera in the Our River (Luxembourg, Europe) has come close to extinction. It consists predominantly of adult animals and will disappear within a few years without assistance. Juvenile mussels cannot survive in the river bed interstices, which are clogged by fine sediments, and rearing methods are needed to help them through this critical period. The objectives of this study were to elucidate the best rearing conditions for juvenile mussels with respect to the food type and density of individuals in order to breed them in the laboratory to a size at which survival in the river is likely. Different food mixtures (combinations of algae, detritus and crushed red bloodworms) were fed to juvenile mussels in plastic boxes containing 500 mL of river water during a period of 110 days. To understand fluctuations in the concentrations of nitrate, nitrite and ammonium between water exchanges, these ions were analysed over a period of 8 days. The best rearing results were achieved with a combination of detritus and algae. This treatment resulted in a growth rate of 189% (up to 1.13 mm (SD ±0.30) per box) with a survival rate of 80% (101 dead mussels (SD ±163.71) per box). The optimum number of mussels per box was 200. When detritus was added to the boxes, levels of nitrite and ammonium were reduced by more than 50% compared with the initial value within 8 days. Without detritus, ion concentrations increased noticeably (ammonium >50%, nitrite >150%), probably explaining higher mortality rates. Juvenile mussels have food reserves for less than 8 days after excystment and need additional food as soon as possible after dropping from the host fish. Juvenile mussels showed the most favourable survival rate and growth rate if fed with a mixture of algae and detritus. Detritus functions not only as a food source but also as a biologically active compound which reduces harmful ions such as ammonium and nitrite in the boxes. Copyright © 2013 John Wiley & Sons, Ltd.

Concentrations of the platinum group elements Pt, Pd, and Rh were analyzed by adsorptive cathodic stripping voltammetry (Pt, Rh) and total-reflection X-ray fluorescence (Pd) in the intestinal helminth Pomphorhynchus laevis and its host Barbus barbus. The fish were caught in the Danube river south of the city of Budapest (Hungary) and were exposed to ground catalytic material for 28 days. Following exposure all three precious metals were taken up and accumulated in host organs and the parasites. Interestingly, in all tissues of the unexposed controls Pt was found, whereas Pd was not present in the muscle of the controls and Rh was not detectable in muscle and intestine of unexposed barbel. All metals were found at significantly higher concentrations in the acanthocephalan than in the tissues of barbel. These results are discussed with respect to the application of P. laevis as an accumulation indicator for metals.

Concentrations of As, Al, Ag, Ba, Bi, Cd, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sb, Sn, Sr, Tl, V and Zn were analyzed by inductively coupled mass spectrometry (ICP-MS) in the intestinal helminth Pomphorhynchus laevis and its host Barbus barbus. The fish were caught in the Danube river downstream of the city of Budapest (Hungary). Ten out of twenty one elements analyzed were found at higher concentrations in the acanthocephalan than in different tissues (muscle, intestine, liver and kidney) of barbel. Considering the fish tissues, most of the elements were present at highest concentrations in liver, followed by kidney, intestine and muscle. Spearman correlation analyses indicate that there is competition for metals between the parasites and the host. The negative relationships between parasite number and metal levels in organs of the barbel support this hypothesis. The bioconcentration factors for Ag, As, Ba, Bi, Cu, Ga, Mn, Pb, Sr, Tl, and Zn showed that the parasites concentrated metals to a higher degree than the fish tissues. They accumulated the metals As, Cd, Cu, Fe, Ni, Pb, Sr and Zn even better than established bioindicators such as the mussel Dreissena polymorpha as revealed by data from the literature. The results presented here emphasize that acanthocephalans of fish are very useful as sentinels for metal pollution in aquatic ecosystems. Ratio of metal concentrations in the parasites and the host tissues provide additional information. Not including acanthocephalans in accumulation bioindication studies with fishes (as still customarily done) may lead to false results.

Die Aufnahme und Anreicherung der Kfzburtigen Platingruppenelemente (PGE) Pt, Pd und Rh durch aquatische Tiere wurde an Dreikantmuscheln, Aalen und Barben untersucht. Hierzu wurden die Testorganismen in Wasser mit Strasenstaub einer stark befahrenen Strase oder mit zerriebenem Autokatalysatormaterial uber mehrere Wochen exponiert und anschliesend Leber und Niere der Fische sowie das Weichgewebe der Muscheln analysiert. Im Rahmen dieser Studien konnte nachgewiesen werden, dass alle drei Edelmetalle durch Fische wie durch Muscheln aufgenommen und angereichert werden. Fur Pd fand sich die hochste Bioverfugbarkeit, gefolgt von Pt und Rh. Das Ausmas der Aufnahme von Pd durchDreissena polymorpha war ca. 5fach hoher als von Pb und 6fach niedriger verglichen mit dem essenziellen Element Cu. In Anbetracht der steigenden Emission von Pd sollte ein Umweltmonitoring die Verbreitung von Pd in der Umwelt klaren.

Intensive agriculture causes increased fine sediment and nutrient runoff into running waters. Despite various approaches to quantify the entry of fine sediment into streams, its biological impact is not well understood. In particular, it is unclear whether the potential effects on the biota can be explained by fine sediment loads alone or in combination with other physicochemical and/or hydrological impacts. In this study, we investigated the impact of fine sediment deposition relative to other impacts on the benthic macroinvertebrates in small headwaters in Luxembourg, a region that is sparsely populated and characterised by agricultural land use on the hills and wooded stream valleys. The surficial-deposited fine sediment, content of inorganic sediment, proportions of organic matter, and carbon to nitrogen (C/N) ratio were recorded 1 year. The stream macroinvertebrate assemblages were recorded in the spring and autumn using multi-habitat sampling. A partial canonical correspondence analysis (pCCA) was applied to quantify and verify the impact of individual sediment components and other environmental variables on the community composition, whereas redundancy analysis (RDA) was used to examine the impact of environmental variables on the macroinvertebrate diversity and functional metrics. Oxygen content, C/N ratio as well as fine gravel explained best both the taxa composition and macroinvertebrate metrics, whereas large-scale variables such as land use were less important. The biological response to oxygen deficits and the C/N ratio of the deposited fine sediment indicate the potential effects of fine sediment deposition through oxygen consumption. Our results show that the chemical composition of the deposited sediment is more important than the amount of sediment, as the C/N ratio alone explained a substantial amount of variance in species composition. Thus, we suggest that future studies on the impact of fine sediment on the macroinvertebrate community should focus on small-scale factors, including the chemical composition of the deposited fine sediment in combination with the physicochemical and hydromorphological stream parameters.

Acanthocephalus rhinensis n. sp. is described from the European eel. Anguilla anguilla (Linnaeus, 1758), collected in the Rhine River near the city of Karlsruhe, Germany. It is the sixth species of Acanthocephalus Koelreuther, 1771 described from European fish. Four other species are known from amphibians. The new species is distinguished from the other 5 species infecting fish by having a 1.2-mm-long proboscis armed with 15-21 rows of 13-16 hooks each, lemnisci about as long as receptacle, oblong and slightly pre-equatorial testes, and thin fusiform eggs, measuring 85-95 X 15-18 micro. Testes in the other European species are usually round to ovate, except in Ac. anguillae (Müller, 1780) Lühe, 1911 where they are also elongated but postequatorial. It aslo has an orange-brown belt encircling the anterior end of the trunk. The comparative distribution of Acanthocephalus in Europe and North America, and the validity of 2 presumably questionable species are discussed, Acanthocephalus falcatus (Froelich, 1789) Lühe, 1911 and Ac. Paronai (Cendorelli, 1897) Meyer, 1932. A dichotomus key distinguishing Ac. rhinensis from the other 9 European species is also included. The new species was only found in 3 of 390 eels examined during 11 yr; this may be related to the changing benthos community in the Rhine River.

In 2003, the parasite fauna of 197 European eelsAnguilla anguilla, captured at three different locations (Laufenburg, Karlsruhe and Beneeden Leeuwen) in the River Rhine, was analysed. The eels harboured a total of 18 species, among them the protozoa (Myxidium giardi, Myxobolus kotlaniandTrypanosoma granulosum), acanthocephalans (Acanthocephalus anguillae, Acanthocephalus lucii, Echinorhynchus truttae, Pomphorhynchus laevis), nematodes (Paraquimperia tenerrima, Pseudocapillaria tomentosa, Camallanus lacustris, Raphidascaris acus, Spinitectus inermisandAnguillicola crassus), cestodes (Bothriocephalus clavicepsandProteocephalus macrocephalus) and monogeneans (Pseudodactylogyrussp.). The parasite fauna at the different locations is discussed with respect to the crustacean fauna present at these locations. The investigation shows that changes in the composition of the crustacean fauna, due to the anthropogenic breakdown of a biogeographic barrier, are reflected in the composition of the intestinal eel parasite fauna.

The fish fauna in the northern part of the upper river Rhine close to the city of Karlsruhe (Germany) was analyzed by collecting fish from the cooling-water intake of a power plant (impingement method) between 1989 and 2001. With this method a total of 36 fish species were recorded. The results were compared between the years as well as with other studies on the fish fauna in this area. Particularly with regard to the physical structure of the river bed and banks, the pre-technical situation of the river Rhine has not been restored. However, the number of fish species has been augmented since the 1970s mainly due to improvements in the water quality and almost all autochthonous fish species are present again. Altogether only three introduced fish species ( Sander lucioperca L., Lepomis gibbosus L., and Carassius auratus gibelio were found in this study. Among the long-distance migrating species three freshwater spawners ( Lampetra fluviatilis , Petromyzon marinus and Salmo trutta trutta ) were detected in addition to the catadromous eel. The eudominant fish species varied between years, i.e. the European eel, Anguilla anguilla , was the eudominant species 1989, whereas this species occurred in much lower numbers during the subsequent sampling campaigns. This clearly indicates that the high dominance of eels is mainly caused by stocking activities in the upper Rhine. In the following years roach, Rutilus rutilus was the eudominant fish species. Overall a positive development of the fish fauna in the upper Rhine over the last 15 years could be observed in terms of fish populations as well as in terms of species richness.