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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)

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.

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.

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.