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 Given that riverine systems exhibit longitudinal environmental gradients from headwater to the mouth of a river, habitat heterogeneity appears to be a major driver of spatial variation in community composition among riverine localities. As freshwater ecosystems are amongst the most endangered ecosystems in the world, community‐based conservation and multiple‐species management are necessary to maintain ecosystem integrity. We used joint species distribution models (JSDMs) to investigate the relative importance of abiotic and biotic factors that are responsible for the distribution and co‐occurrence of species in riverine ecosystems. Location Central and northern Europe. Methods We examined the general patterns of species assemblage of two endangered freshwater mussel species (Margaritifera margaritifera and Unio crassus) and their associated fish communities. We examined the patterns of positive or negative co‐occurrence in mussel and fish species and identified shared abiotic responses between mussel–host pairs. Results We found that the relative importance of abiotic and residual factors and patterns of significant species correlations varied among taxa: significant residual correlations were prevalent among fish species, whereas mussel occurrences were exclusively explained by abiotic factors. Mussels and their fish hosts generally had shared abiotic responses with some mismatched responses between mussel–host pairs. Main conclusions Given that the composition of communities were tightly linked with abiotic factors and residual correlations, the results have significant implications for the conservation and restoration of aquatic communities. This study highlights the necessity to simultaneously consider environmental factors and species co‐occurrences in the modelling of species distributions and assemblages of riverine communities. Such a holistic community conservation approach can reveal ecological similarities and differences among species, which can help us avoid conflicts among target‐species conservation plans.
Recruitment and dispersal of freshwater mussels of the Unionoida is strongly linked to their host fishes on which the larvae develop into juvenile mussels. Host limitation has been suggested as one of the potential causes for the decline of the formerly widespread thick‐shelled river mussel (Unio crassus), although quantitative data analysing the importance of this factor are still missing. In this study, the status of host fish populations was assessed in nine U. crassus streams within the Danube drainage system situated in southern Germany. In particular, links between recruitment patterns of U. crassus populations, fish species composition and quantitative data of host fish densities in functional and non‐functional streams were established. Fish species composition and richness ranged between three and nine species with no difference in presence data between functional and non‐functional streams. Despite this high variability, functional U. crassus streams with high proportions of juvenile mussels had significantly higher (mean: 40 Ind. per 100 m2) densities of primary hosts (Phoxinus phoxinus, Squalius cephalus, Gasterosteus aculeatus) than non‐functional streams (mean: 8 Ind. per 100 m2). In contrast, no relationship was found between the numbers and densities of juvenile mussels and densities of poor hosts as well as of non‐hosts. The results of this study indicate that the recruitment status of U. crassus strongly depends on the density of primary host fish species. Host limitation is likely to play a major role in a lack of juvenile recruitment and consequently in the decline of central European U. crassus populations. Therefore, future conservation for this endangered mussel species should more thoroughly incorporate management of host fish species and consider both the requirements of mussels and their hosts in habitat restoration. Copyright © 2014 John Wiley & Sons, Ltd.
ABSTRACT1. Conservation and restoration strategies require knowledge of the autecology of target species. The thick-shelled river mussel Unio crassus is an endangered freshwater bivalve with largely unknown habitat preferences. In this study, hydrological and substrate parameters including shear stress, flow velocity and penetration resistance of substrate were examined in relation to mussel presence/absence data in six streams with recruiting and self-sustaining populations to derive information on the hydrological and substrate habitat requirements of the species. The results indicate that the hydrological and substrate characteristics of U. crassus habitat are broader than expected. In contrast to the assumption that it depends on moderate to high flows (>0.3 m s À1 ), streams with low water flow and soft substrate were also identified as suitable habitats. 6. Functional characteristics of the substrate, especially stability and areas with low shear stress (<1.5 N cm À2 ), seem to be of great importance for the persistence of the species, and monitoring protocols used at present for habitat assessment of U. crassus should be updated.
In spite of their conservation importance, only a fraction of lakes and streams globally – including their catchments – are currently covered by conservation areas. To identify conservation gaps, assessing the spatial distribution of biodiversity in relation to conservation areas is a promising approach. A gap‐analysis approach was used to evaluate the protection status of the habitats of two endangered freshwater mussel species, Margaritifera margaritifera (Linnaeus, 1758) and Unio crassus (Philipsson, 1788), in the Federal State of Bavaria, Germany. First, ecological niche models (ENMs) were developed for both mussel species based on presence‐only data in order to identify suitable habitats. Second, binary maps of suitable and unsuitable habitats for the species were used to compare different categories of currently protected areas in a gap analysis. The ENMs for M. margaritifera revealed a spatially restricted distribution with good model performance, whereas the spatial distribution of U. crassus was wider and the model performance was weaker. For M. margaritifera, a higher percentage of suitable habitat is already under some sort of protection, whereas for U. crassus only half of the suitable habitats are under protection. The results suggest that suitable habitats of both species are not sufficiently protected. More effective conservation of M. margaritifera and U. crassus requires separate management: increasing the respective protection categories of already protected habitats of M. margaritifera and incorporating an increased area of suitable habitats under legal protection for U. crassus.
1. The freshwater pearl mussel (Margaritifera margaritifera) and the thick-shelled river mussel (Unio crassus) are relatively widespread across Europe, but are strongly declining and are now protected by the European Habitats Directive. In the course of this study, 20 pearl mussel and 14 thick-shelled river mussel streams in Bavaria, Germany, were investigated.2. The mussel populations were mapped to determine population size and age structure. For the assessment of habitat quality, host fish abundance and physicochemical parameters were investigated, e.g. substratum quality, water chemistry, redox potential, and turbidity. Furthermore, potential risks for the populations such as predation or river maintenance were also recorded and assessed.3. The average population size and recruitment rates of M. margaritifera populations were lower than in U. crassus populations, with 3517 (2.2% juveniles) compared with 5566 (41.4% juveniles) individuals, respectively. On average, 22.3% of particles were smaller than 0.85 mm in diameter at M. margaritifera sites, whereas the mean proportion of fine particles at U. crassus sites was twice as high, at 41.3%.Other parameters such as redox potential or electric conductivity also indicated more favourable habitat conditions in M. margaritifera streams. Unio crassus seems to be less vulnerable to adverse substratum texture and increased nutrient levels than M. margaritifera.4. The main threats for U. crassus were physical habitat destruction, predation by muskrat, or a lack of host fish, whereas M. margaritifera mainly suffered from siltation leading to a lack of oxygen supply to the interstitial zone, affecting recruitment. Consequently, conservation strategies need to be species-specific and address stream-specific reasons for decline. As a basis, accurate and comparable monitoring data are necessary, which implies the standardization of monitoring protocols.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.