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.

Freshwater mussels are declining globally, and effective conservation requires prioritizing research and actions to identify and mitigate threats impacting mussel species. Conservation priorities vary widely, ranging from preventing imminent extinction to maintaining abundant populations. Here, we develop a portfolio of priority research topics for freshwater mussel conservation assessment. To address these topics, we group research priorities into two categories: intrinsic or extrinsic factors. Intrinsic factors are indicators of organismal or population status, while extrinsic factors encompass environmental variables and threats. An understanding of intrinsic factors is useful in monitoring, and of extrinsic factors are important to understand ongoing and potential impacts on conservation status. This dual approach can guide conservation status assessments prior to the establishment of priority species and implementation of conservation management actions.

The freshwater pearl mussel (Margaritifera margaritifera) is an endangered species in Europe, protected nationally and internationally, but with a steadily declining range and abundance owing to pressures such as pollution, river engineering, and illegal exploitation. Despite this, no consistent approaches have been developed around Europe for monitoring pearl mussel populations and their habitats. To address this need, experts on pearl mussel ecology from 11 countries met at a series of workshops in order to develop a protocol for monitoring, published under the auspices of the European Committee for Standardization (CEN). This standard is unique, as it is the first CEN standard dedicated to a single species of conservation concern. The standard is aimed at scientists, conservation bodies, and environmental regulators, and can be used for designing national monitoring programmes as well as reporting on the conservation status of pearl mussel populations under the European Habitats Directive. It contains guidance at the individual site level to determine why populations are failing to recruit, but also addresses the need for a wider‐scale approach to ensure that catchment developments do not have adverse impacts on rivers containing pearl mussels. A pearl mussel monitoring programme needs to investigate the size and viability of populations, as well as the fish hosts (Atlantic salmon, Salmo salar, or brown trout, Salmo trutta) on which pearl mussel larvae depend. Water quality, including variables such as dissolved oxygen, acid–base chemistry, and nutrient levels, is also an essential monitoring component, together with the physical features of the river bed, river flow regimes, and sediment dynamics. It is hoped that this pan‐European approach will improve the ability to compare data across many countries, and will ultimately ensure that the results of monitoring are translated into measures for improving the conservation status of the freshwater pearl mussel throughout its range.

With the biodiversity crisis continuing unchecked, we need to establish levels and drivers of extinction risk to effectively allocate conservation resources and develop targeted actions. Given that threat appears particularly high in freshwaters, we assessed the extinction risk of 1,500 randomly selected freshwater molluscs using the IUCN Red List Categories and Criteria, as part of the Sampled Red List Index project. We show that close to one third of species in our sample are estimated to be threatened with extinction, with highest levels of threat in the Palearctic, Australasia and Nearctic and among gastropods. Threat levels were higher in lotic than lentic systems. Twenty-seven species were classified as Extinct (eight bivalves and 19 gastropods), mostly from the Nearctic realm and lotic systems. Pollution and the modification of natural systems (e.g. through damming and water abstraction) were the most frequently reported threats to freshwater molluscs, with some regional variation. Given that we found little spatial congruence between species richness patterns of freshwater molluscs and other freshwater taxa, new additional conservation priority areas emerge from our study. We discuss the implications of our findings for freshwater mollusc conservation and important next steps to estimate trends in freshwater mollusc extinction risk over time.

. (2015) Effects of substrate size and cleaning regime on growth and survival of captive-bred juvenile freshwater pearl mussels, Margaritifera margaritifera (Linnaeus, 1758).