Karel Douda

Conservation status of freshwater mussels in Europe: state of the art and future challenges.

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 role of host specificity in explaining the invasion success of the freshwater mussel Anodonta woodiana in Europe

Several freshwater mussel species represent some of the most problematic invasive species and have considerably altered ecosystems worldwide. Their invasion potential has been partially attributed to their free-living larvae, which have a high dispersal capability. We investigated the invasion potential of Anodonta (Sinanodonta) woodiana, a species of East Asian unionid mussel established worldwide despite having an obligatory parasitic stage (glochidium), which must encyst on host fish. The invasion success of A. woodiana has been attributed to the success of worldwide introductions of its sympatric fish hosts. We experimentally found, however, that A. woodiana is a broad host generalist, which can complete its development on all eight fish species tested, both coinvasive and native. Subsequently, we used a data on the occurrence and relative abundance of potential hosts in river habitats in the Czech Republic to project scenarios of the effect of host availability on A. woodiana invasion. We found that host availability does not constitute a major limit for A. woodiana to colonise most aquatic habitats in Central Europe. In addition, we investigated seasonal dynamics of A. woodiana reproduction and did not detect any limitations of its reproduction by ambient water temperatures typical of a Central European lowland river. Consequently, we predict that A. woodiana may further increase the speed and range of its invasion and we discuss possible consequences to native habitats and communities, especially to the endangered species of unionid mussels.

Host compatibility as a critical factor in management unit recognition: population‐level differences in mussel–fish relationships

Summary 1. The recognition of management units (MUs) that respect interpopulation distinctions in management needs is central to many biological applications addressing species conservation, biological invasions and ecosystem processes. 2. We present a methodological approach for the evaluation of population-level differences in the host compatibility of natural populations of affiliate (dependent) species. Two experiments were performed to diagnose the sources of variability in the relationships between an endangered freshwater mussel Unio crassus and its host fish species in a fragmented river system in Central Europe. 3. Despite the common approach applied to the conservation of U. crassus throughout the study area, we identified differences in the ability of U. crassus to infest particular host fish species between nearby and recently isolated mussel populations. These differences could strongly influence their reproductive success under a constant conservation regime. 4. The observed differences were accompanied by genetic and morphometric distinctions, as revealed by microsatellite, mtDNA and elliptic Fourier descriptor analyses. The genetic data indicated substantial reproductive isolation, which could have resulted in adaptive or random changes responsible for the differences in host compatibility. 5. We showed that experimental testing of physiological host compatibility can be effectively used for the detection of different MUs of U. crassus, with direct implications for the management of host populations. In combination with traditional genetic and morphometric techniques, this approach may provide a general framework for the recognition and care of management units of affiliate species. 6. Synthesis and applications. Population-level evaluations of host compatibility should be utilized in management unit recognition and the formulation of management targets for affiliate species. We demonstrated that small-scale cross-compatibility testing can be effectively used to diagnose the sources of variability in host relationships with direct management implications. This approach can enhance the targeting of management actions in many biological applications addressing species conservation, biological invasions and ecosystem processes.

Development of alder carr after the abandonment of wet grasslands during the last 70 years

Abstract• The secondary succession of wet grasslands to communities of alder carr dominated by Alnus glutinosa was recorded in different parts of Europe during the 20th century. However, knowledge of such development of alder carr remains insufficient.• The development of alder carr was reconstructed at five sites in the Czech Republic, using historical aerial photographs and methods of dendrochronology. The aims were to investigate the succession from wet grasslands to alder carr at sites previously intensively managed for agriculture and to find out the role of fluctuations in the groundwater table, caused by artificial drainage channels, in the observed stand dynamics and tree growth.• The spread of forest (i.e., an increase in forest cover) predominated until the 1970s at all sites. This trend was disrupted by a large-scale dieback of forest stands in four of the five sites after the 1970s, followed by an increase in patch heterogeneity, as indicated by landscape metrics. The radial growth increment in Alnus glutinosa has been affected predominately by local environmental factors, probably including the changing degree of waterlogging. Forest dieback was presumably connected with a lesser extent of drainage channels.• Our results indicate that observed successional pathways at sites of alder carr were probably caused by local changes in the groundwater table.Résumé• La succession secondaire des prairies humides en communautés de taillis d’aunes dominées par Al-nus glutinosa a été enregistrée dans différentes parties de l’Europe au cours du 20e siècle. Toutefois, la connaissance du développement de taillis d’aunes reste insuffisante.• Le développement de taillis d’aunes a été reconstruit dans cinq sites en République Tchèque, à l’aide de photographies aériennes historiques et des méthodologies de la dendrochronologie. Les objectifs étaient d’étudier la succession de prairies humides en taillis d’aunes sur des sites précédemment exploités intensivement par l’agriculture et de découvrir le rôle des fluctuations de la nappe phréatique, causées par le drainage artificiel des canaux, et d’observer la dynamique des peuplements et la croissance des arbres.• La progression de la forêt (c’est-à-dire, l’augmentation du couvert forestier) a prédominé jusque dans les années 1970 dans tous les sites. Cette tendance a été perturbée par un vaste dépérissement des peuplements forestiers dans quatre des cinq sites après les années 1970, suivie par une augmentation de l’hétérogénéité des bouquets d’arbres, comme indiqué par les paramètres du paysage. L’augmentation de la croissance radiale de Alnus glutinosa a été affectée principalement par les facteurs environnementaux, y compris sans doute l’évolution du degré d’engorgement. Le dépérissement des forêts est probablement lié à une moindre importance des canaux de drainage.• Nos résultats indiquent que les voies de succession observées sur les sites des taillis d’aunes ont probablement été causées par des changements locaux dans la nappe phréatique.

An invasive species reverses the roles in a host-parasite relationship between bitterling fish and unionid mussels

The impact of multiple invading species can be magnified owing to mutual facilitation—termed ‘invasional meltdown’—but invasive species can also be adversely affected by their interactions with other invaders. Using a unique reciprocal host–parasite relationship between a bitterling fish (Rhodeus amarus) and unionid mussels, we show that an invasive mussel reverses the roles in the relationship. Bitterling lay their eggs into mussel gills, and mussel larvae parasitize fish. Bitterling recently colonized Europe and parasitize all sympatric European mussels, but are unable to use a recently invasive mussel, Anodonta woodiana. The parasitic larvae of A. woodiana successfully develop on R. amarus, whereas larvae of European mussels are rejected by bitterling. This demonstrates that invading species may temporarily benefit from a coevolutionary lag by exploiting evolutionarily naive hosts, but the resulting relaxed selection may facilitate its exploitation by subsequent invading species, leading to unexpected consequences for established interspecific relationships.

Population-specific responses to an invasive species

Predicting the impacts of non-native species remains a challenge. As populations of a species are genetically and phenotypically variable, the impact of non-native species on local taxa could crucially depend on population-specific traits and adaptations of both native and non-native species. Bitterling fishes are brood parasites of unionid mussels and unionid mussels produce larvae that parasitize fishes. We used common garden experiments to measure three key elements in the bitterling–mussel association among two populations of an invasive mussel (Anodonta woodiana) and four populations of European bitterling (Rhodeus amarus). The impact of the invasive mussel varied between geographically distinct R. amarus lineages and between local populations within lineages. The capacity of parasitic larvae of the invasive mussel to exploit R. amarus was higher in a Danubian than in a Baltic R. amarus lineage and in allopatric than in sympatric R. amarus populations. Maladaptive oviposition by R. amarus into A. woodiana varied among populations, with significant population-specific consequences for R. amarus recruitment. We suggest that variation in coevolutionary states may predispose different populations to divergent responses. Given that coevolutionary relationships are ubiquitous, population-specific attributes of invasive and native populations may play a critical role in the outcome of invasion. We argue for a shift from a species-centred to population-centred perspective of the impacts of invasions.

Parasite-induced increases in the energy costs of movement of host freshwater fish.

Parasitization by the larvae (glochidia) of freshwater mussels can cause harm to a fishs gills, resulting in less effective respiration and/or reduced activity by the host fish. The impact of glochidia infections on the hosts physiology remains poorly understood, and no information is available concerning energy consumption in parasitized fish. Hence, we obtained glochidia of the invasive unionid mussel Sinanodonta (Anodonta) woodiana and experimentally infected common carp, Cyprinus carpio, tagged with physiological sensors to measure energy consumption. We tested the hypothesis that parasitization affects energy consumption in the host fish, reflected as higher energy costs for movement and reduced movement activity over eight days post-infection within a twenty-four-hour cycle. Parasitized fish showed higher energy costs of movement; however, no changes in movement activity were found compared with activity in control fish. Significantly increased biochemical indices were measured in host fish blood samples, including aspartate (AST) and alanine (ALT) aminotransferase levels, indicating liver injury, and high concentrations of potassium (K+), signifying kidney injury (hyperkalemia). Increased Cl- concentrations indicate gill dysfunction. Our results show that the energy costs due to glochidia parasitization are independent of overall movement activity patterns and vary in time according to the parasitic phase and the diurnal cycle. Moreover, the side effects of parasitization have a more important impact on fish hosts than has been shown in previous reports.

Species-specific pattern of crayfish distribution within a river network relates to habitat degradation: implications for conservation

Abstract The degradation of aquatic habitats has increasingly become one of the most important factors influencing the distribution of freshwater species worldwide. We analysed the occurrence of three crayfish species, Astacus astacus, Austropotamobius torrentium and Orconectes limosus, in relation to habitat degradation status (based on Directive 2000/60/ES), stream morphology, geographical characteristics and land cover. In total, we analysed 6,768 sites within the Czech Republic (Central Europe), of which 6,187 sites lacked crayfish; among the remainder, A. astacus was present in 507 sites, O. limosus occurred in 44 sites and A. torrentium was present in only 30 sites. The analysis revealed that A. astacus preferred streams of better water quality that were not surrounded by agricultural land or settlements. This species also preferentially occurred in smaller streams with stony bottom substrata that were located at higher altitudes. Austropotamobius torrentium occurrence was associated with the natural character of the water body and the presence of protected areas at higher altitudes. Conversely, the non-native crayfish species O. limosus was typically recorded at lower altitudes in downstream reaches surrounded by agricultural land and with deteriorated water quality. The degree of environmental (human) pressure besides differences in habitat characteristics at sites with ICS and NICS may be of general importance for conservation strategies aimed at central European native crayfish species, primarily because the habitat-driven co-occurrence pattern (and its possible changes in the future) may strongly influence interspecific relationships, such as direct competition and the spread of infectious diseases between crayfish species.

Within-river variation in growth and survival of juvenile freshwater pearl mussels assessed by in situ exposure methods

The early post-parasitic phase is considered to be the most vulnerable life stage of the endangered freshwater pearl mussel (Margaritifera margaritifera), yet little is known about the spatial variability in juvenile performance at a river scale. The main aim of this study was to determine within-river variation in habitat suitability for juvenile M. margaritifera. The growth and survival rates of juveniles (one and two year old) were measured in the Vltava River (Czech Republic) in relation to several physical and chemical variables using a total of 166 bioindication units (individual mesh cages and sandy boxes) during two thermally different vegetation seasons. Three spatial scales were studied: a longitudinal river profile, bottom habitat types, and hyporheic microhabitats. Both the survival rate and growth of the exposed juveniles varied considerably within the studied river. The effect of the longitudinal river profile and the roles of temperature, oxygenation within microhabitats, episodic pollution, and exposure method were demonstrated. This study represents the first example of a hierarchized approach to the assessment of a riverine mussel biotope with the use of bioindication methods. The results demonstrate the importance of the scale and bioindication method used in understanding the suitability of a river environment to juvenile freshwater mussels.

Altered thermoregulation as a driver of host behaviour in glochidia-parasitised fish

ABSTRACT Parasites alter their host behaviour and vice versa as a result of mutual adaptations in the evolutionary arms race. One of these adaptations involves changes in host thermoregulation, which has the potential to harm the parasite and thereby act as a defence mechanism. We used a model of the brown trout (Salmo trutta) experimentally parasitised with glochidia ectoparasitic larvae from the endangered freshwater pearl mussel (Margaritifera margaritifera) to reveal whether parasitisation alters fish behavioural thermoregulation. A study using radiotelemetry temperature sensors was performed during almost one year of the M. margaritifera parasitic stage. Glochidia-infested S. trutta altered their thermoregulation through active searching for habitats with different thermal regimes. The general preference for temperatures in infested fish varied and was either above or below the temperature preferred by uninfested individuals. Infested fish also preferred different temperatures across localities, whereas uninfested fish maintained their thermal preference no matter which stream they inhabited. Glochidia further induced the expression of a behavioural syndrome among S. trutta personality traits, suggesting that it might increase the probability that the fish host would occur in the glochidia temperature optimum. Our findings present the first evidence that thermoregulation plays a fundamental role in the relationship of affiliated mussels and their fish hosts. Incorporating thermoregulation as a factor in the study of this relationship can help to interpret results from previous behavioural studies, as well as to optimise management measures related to endangered mussels. Summary: Thermoregulation plays a fundamental, up to now neglected, role in the relationship of endangered affiliated mussels and their fish hosts.