Freshwater mussels are benthic suspension feeders that influence microbial dynamics in rivers and lakes. However, interactions between freshwater bivalves and fish-pathogenic bacteria remain poorly understood. We evaluated the capacity of the native freshwater mussel Diplodon chilensis to remove the fish pathogen Flavobacterium psychrophilum from the water column and assessed short-term physiological responses to bacterial exposure. Mussels were exposed to increasing bacterial concentrations (105–107 CFU ml−1), and filtration performance was evaluated over 8 h. A complementary assay evaluated digestive activity, immune responses, and tissue integrity after 24 h of exposure to bacterial concentrations that were efficiently removed during the filtration experiment 105 and 106 CFU ml−1, plus a sub-outbreak concentration (104 CFU ml−1). D. chilensis rapidly reduced bacterial concentrations at 105 and 106 CFU ml−1, reaching near-complete removal within 8 h while maintaining high clearance rates. Higher bacterial loads reduced filtration performance, suggesting functional limits at extreme microbial loads. Physiological analyses indicated activation of digestive and cellular immune responses without evidence of acute tissue damage. These results demonstrate that D. chilensis can effectively filter F. psychrophilum while maintaining short-term physiological integrity. Such interactions highlight the potential role of freshwater mussels in modulating microbial assemblages in freshwater systems, including fish pathogens.
Biological invasions commonly occur in series, leading to new interactions between multiple invaders in novel habitats. Their coexistence or competitive exclusion depends on the width and overlap of their habitat preferences. We evaluated the habitat preferences of North American crayfishes invasive in Europe: Faxonius limosus (FL), Procambarus clarkii (PC) and Procambarus virginalis (PV), to check their selectivity for substratum grain sizes, shelter sizes, and shells of various bivalve species as shelters. All the species exhibited overlapping grain size preferences (diameter: 2 mm), PV being the least selective (preference extending to 5 mm). FL selected smaller shelters than PC. FL and PC preferred shells of the alien Sinanodonta woodiana over native unionid mussels, whereas PV was non-selective for unionid shells. All species avoided the smaller Corbicula shells. Altogether, in our study, FL was the most, whereas PV the least selective, and PC the most explorative. The high overlap of habitat preferences and low probability of habitat partitioning suggests that the coexistence of these crayfishes will be temporary, and FL is likely to get displaced by new Procambarus invaders, P. clarkii being more explorative and aggressive, P. virginalis being less selective.
Whiting in the Black Sea is assessed as a single shared stock within the General Fisheries Commission for the Mediterranean framework using biological data provided by the riparian countries. Because these data originate from different national monitoring programmes, uneven size coverage may influence growth estimation. To evaluate the implications of such data limitations, a harmonised multinational age–length dataset from Bulgaria, Georgia, Romania, and Türkiye was analysed using both classical and Bayesian von Bertalanffy growth models. Jointly standardised otolith readings were used to minimise reader-related bias, while biologically informed priors were incorporated in the Bayesian framework to stabilise estimation where parts of the size spectrum were poorly represented. Bayesian estimates were less affected by truncated size distributions while preserving the main growth patterns observed in the classical analyses. Although similar regional patterns were evident under both modelling approaches, the available data do not allow the relative contributions of sampling structure and biological variation to be distinguished. Growth-based natural mortality trajectories further demonstrated that differences in growth estimates propagate into assessment parameters. These findings highlight the value of Bayesian growth modelling for shared stock assessments based on heterogeneous multinational datasets, while emphasising the need for cautious biological interpretation when sampling coverage is uneven.
Freshwater ecosystems have long been exposed to multiple human-mediated stressors, including the introduction and spread of non-native species. Although invasion biology has produced numerous freshwater case studies, the role of waterbody heterogeneity in shaping the invasion history of freshwater catchments has rarely been assessed. To address this knowledge gap, we reconstructed the appearance history of non-native aquatic species in the catchment of the largest shallow lake in Central Europe. The catchment comprises a diverse mosaic of waterbodies, including a large shallow lake (Lake Balaton), a thermal lake (Lake Hévíz), fishponds, and several small watercourses. We found that the arrival of new species was strongly associated with waterbodies differing in environmental characteristics, intensity of human pressures, and pressure histories. Lake Balaton acted as the primary entry point for species introduced via shipping activity. In contrast, Lake Hévíz disproportionately contributed to the appearance of non-native species of Afrotropical origin, consistent with aquarium-mediated introductions. Fishponds represented the major source habitat for species introduced through unintentional releases linked to fish production. Overall, our results demonstrate that heterogeneity of waterbodies plays a substantial role in structuring invasion history in freshwater catchments and should be explicitly incorporated into invasion assessment and management.
Small hydropower plants are increasingly recognised as important drivers of hydromorphological alteration in river ecosystems, yet their effects on benthic diatoms remain insufficiently understood. We investigated the taxonomic and functional responses of benthic diatom assemblages to two operational-channel hydropower plants along the Hernád River (Hungary). Twenty-five benthic samples were collected from the main channel, operational channels, and hydromorphologically modified river sections. Taxonomic composition differed markedly among habitat types, whereas functional trait composition showed weaker differentiation, indicating functional redundancy despite pronounced taxonomic turnover. Species richness, effective Shannon diversity, and evenness did not differ significantly among habitat categories; however, functional richness and functional divergence revealed significant differences, highlighting functional reorganisation associated with hydromorphological modification. Significant distance–decay relationships were detected within both operational channels and modified river sections, suggesting that spatial structuring persisted despite river fragmentation. Fifteen threatened taxa and several non-native species were recorded, but neither habitat-specific segregation of threatened taxa nor invasion hotspots were identified. Our results demonstrate that small hydropower plants can substantially modify the taxonomic and functional organisation of benthic diatom assemblages without necessarily reducing local taxonomic diversity. The observed responses suggest community reorganisation rather than biodiversity loss and highlight the importance of maintaining longitudinal connectivity in regulated rivers.
