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.

Aim At what spatial extent are biotic interactions discernible influences on the distribution and abundance of species in river networks? We address this question with analyses of data from river networks for Margaritifera margaritifera, a freshwater mussel that passes its larval stage attached to a host fish.Location Twenty river networks in Galicia, north-western Spain.Methods A maximum-entropy approach was implemented to model the species' distribution. Geostatistical mixed models were used to analyse the mussel's abundance in dendritic river networks. Predictor variables included the abundance and biomass of host fish (biotic interactions) and abiotic predictors for climate, geology and land-form.Results Maxent models of species distribution were improved by 4.5% in terms of the area under the receiver-operating characteristic curve (AUC) by the inclusion of biotic interactions. Host-fish predictors contributed 63% of the Maxent model prediction of mussel presence. A geostatistical mixed model explained 52% of the variance in mussel abundance when including all the mussel abundance sites in the study area; abiotic predictors had no significance and salmonid biomass and resident trout population density were the only significant biotic predictors, together explaining 2.4% of the variance. An autocovariate representing biotic interactions between mussels and fish explained 11.7% of the variance. Using only sites where migratory host fish were present (n = 149), a mixed model explained more variance (78%) and the contribution from the autocovariate for parasite-host interactions was about three times larger than for the model including all sites (n = 419). The spatial autocorrelation from mussel-fish interactions had a spatial extent (geostatistical range) greater than 15 km.Main conclusions Interactions between mussels and their larval hosts in river networks are manifested in spatial patterns of species distribution and abundance in this region, encompassing 20 river networks. The directional topology of dendritic river networks strongly supports the upstream dispersal of mussels by parasitized host fish as a component of spatial autocorrelation in mussel abundance.

Fish populations globally are susceptible to endangerment through exploitation and habitat loss. We present theoretical simulations to explore how reduced adult survival (age truncation) might affect short-lived freshwater fish species in human-altered contemporary environments. Our simulations evaluate two hypothetical "average fish" and five example fish species of age 1 or age 2 maturity. From a population equilibrium baseline representing a natural, unaltered environment we impose systematic reductions in adult survival and quantify how age truncation affects the causes of variation in population growth rate. We estimate the relative contributions to population growth rate arising from simulated temporal variation in age-specific vital rates and population structure. At equilibrium and irrespective of example species, population structure (first adult age class) and survival probability of the first two adult age classes are the most important determinants of population growth. As adult survival decreases, the first reproductive age class becomes increasingly important to variation in population growth. All simulated examples show the same general pattern of change with age truncation as known for exploited, longer-lived fish species in marine and freshwater environments. This implies age truncation is a general potential concern for fish biodiversity across life history strategies and ecosystems. Managers of short-lived, freshwater fishes in contemporary environments often focus on supporting reproduction to ensure population persistence. However, a strong focus on water management to support reproduction may reduce adult survival. Sustainability management needs a focus on mitigating adult mortality in human-altered ecosystems. A watershed spatial extent embracing land and water uses may be necessary to identify and mitigate causes of age truncation in freshwater species. Achieving higher adult survival will require paradigm transformations in society and government about water management priorities.

ABSTRACT1. Extensive assessments of a species distribution, its variation in density and demographic status across environments are crucial to develop successful conservation efforts.2. The freshwater pearl mussel (Margaritifera margaritifera) is considered one of the most endangered freshwater bivalves with many recovery efforts continuing throughout its geographic range. The distribution and conservation status of M. margaritifera are not well documented in the Iberian Peninsula. Galicia (NW Iberian Peninsula) represents nearly 70% of the historical distribution of the species in the southern limit of its European range.3. An extensive field survey was conducted in two phases at 2436 locations. The presence and density of M. margaritifera was determined at 555 sampling points spread across 54 rivers that belong to 23 drainage basins in Galicia. The present work has more than doubled the number of rivers known to provide habitat for this endangered species in the Iberian Peninsula.4. In Galicia the species is heterogeneously distributed with a highly variable density of individuals within and between rivers. For example, within the River Camba density ranged from 0.02 to 47.8 ind m -2 . The maximum density detected in a sample was 332 ind m -2 . Twelve rivers in Galicia are thought to have more than 5000 individuals, and small individuals were found in 11 rivers. 5. High rates of decline and extinction of M. margaritifera populations are known in some areas and the main threat to unionoid bivalves is a lack of natural recruitment. Thus, Galician populations are important for providing new opportunities for conservation of the species in Europe because it is vitally important to find the reasons for recruitment failure.

Aim:We apply a novel approach in a spatial network context to identify factors influencing a parasite-host system and to distinguish focal areas for conservation of interacting species.Location: Twenty river networks in southern Europe (Spain) Methods: Spatial stream network (SSN) models were applied to analyse and predict density and biomass of interacting species in river networks. Density of an endangered freshwater mussel (parasite) and biomass data of its host fish were response variables for models with fixed-effect biotic and abiotic predictors and three random effect models for spatial covariance. Universal kriging with the SSN models was used to obtain predictions for parasite density and host biomass for the entire study region.Results: Spatial stream network (SSN) models fitted separately for parasite density and host biomass explained 75% and 77% of the variance, respectively. Predictors explained 5% of the variance for the parasite and 14% for the host. Host biomass was the most important predictor of parasite density. The tail-up and tail-down spatial covariances fitted to the residual variance explained more than a half of the total variance in both models. Significant biotic and abiotic predictors differed between the parasite and host models. Combining model predictions for parasite density and host biomass identified areas where different strategies might be employed to conserve biotic interactions.Main conclusions: Conservation of biotic interactions requires consideration of respective ecologies of the interacting species. In a network environment, connectivity of habitats can be an important determinant for occurrence of biotic interactions.Spatially explicit analyses, such as the SSN, can identify focal areas for conservation of biotic interactions. Conservation focused on biotic interactions, as opposed to a single species, could yield benefits to the focal species, the biotic community with which they occur and the ecosystem that supports them. K E Y W O R D Sfreshwater mussels, geostatistics, parasite-host biotic interactions, Salmonidae, spatial stream network models, universal kriging