The recovery of European freshwater biodiversity has come to a halt.

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss1. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity2. Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

Invasion impacts and dynamics of a European-wide introduced species.

Globalization has led to the introduction of thousands of alien species worldwide. With growing impacts by invasive species, understanding the invasion process remains critical for predicting adverse effects and informing efficient management. Theoretically, invasion dynamics have been assumed to follow an "invasion curve" (S-shaped curve of available area invaded over time), but this dynamic has lacked empirical testing using large-scale data and neglects to consider invader abundances. We propose an "impact curve" describing the impacts generated by invasive species over time based on cumulative abundances. To test this curve's large-scale applicability, we used the data-rich New Zealand mud snail Potamopyrgus antipodarum, one of the most damaging freshwater invaders that has invaded almost all of Europe. Using long-term (1979-2020) abundance and environmental data collected across 306 European sites, we observed that P. antipodarum abundance generally increased through time, with slower population growth at higher latitudes and with lower runoff depth. Fifty-nine percent of these populations followed the impact curve, characterized by first occurrence, exponential growth, then long-term saturation. This behaviour is consistent with boom-bust dynamics, as saturation occurs due to a rapid decline in abundance over time. Across sites, we estimated that impact peaked approximately two decades after first detection, but the rate of progression along the invasion process was influenced by local abiotic conditions. The S-shaped impact curve may be common among many invasive species that undergo complex invasion dynamics. This provides a potentially unifying approach to advance understanding of large-scale invasion dynamics and could inform timely management actions to mitigate impacts on ecosystems and economies.

Microbial faecal pollution of river water in a watershed of tropical Ethiopian highlands is driven by diffuse pollution sources.

Tropical communities in the developing world depend heavily on riverine systems for their socioeconomic development. However, these resources are poorly protected from diffuse pollution, and there is a lack of quantitative information regarding the microbial pollution characteristics of riverine water, despite frequently reported gastrointestinal diseases. The aim of our study was to apply faecal taxation (i.e., faecal pellet counting in representative test areas to estimate the potential availability of diffuse pollution sources) in combination with a detailed microbiological faecal pollution analysis in a riverine environment to elucidate the importance of diffuse pollution. To realize this approach, ambient faecal pellets, a multiparametric data set for standard faecal indicator bacteria (SFIB), including Escherichia coli, Clostridium perfringens spores and enterococci from catchment soil and river water, and a number of riverine water physicochemical variables were analysed during a one-year cycle. We demonstrated that the abundance of ambient faecal pellets, which were consistently counted at reference sites in the catchment, was associated with faecal pollution in the river water. Water SFIB, dissolved oxygen, nutrients, conductivity and total suspended solids were strongly linked with the abundance of ambient faecal pellets in the river catchment, as demonstrated by principal component analysis (PCA). Elevated concentrations of SFIB in the riverine water in the absence of rainfall also suggested the direct input of faecal bacteria into the riverine water by livestock (e.g., during watering) and humans (e.g., during bathing). Statistical analyses further revealed that the microbiological water quality of the investigated riverine water was not influenced by SFIB potentially occurring in the soil. This study demonstrates the importance of diffuse faecal pollution sources as major drivers of the microbiological quality of riverine water in the Ethiopian highlands. In addition, the new successfully applied integrated approach could be very useful for developing predictive models, which would aid in forecasting riverine microbiological quality in tropical developing countries.

Integrative taxonomy by molecular species delimitation: multi-locus data corroborate a new species of Balkan Drusinae micro-endemics.

BACKGROUND: Taxonomy offers precise species identification and delimitation and thus provides basic information for biological research, e.g. through assessment of species richness. The importance of molecular taxonomy, i.e., the identification and delimitation of taxa based on molecular markers, has increased in the past decade. Recently developed exploratory tools now allow estimating species-level diversity in multi-locus molecular datasets. RESULTS: Here we use molecular species delimitation tools that either quantify differences in intra- and interspecific variability of loci, or divergence times within and between species, or perform coalescent species tree inference to estimate species-level entities in molecular genetic datasets. We benchmark results from these methods against 14 morphologically readily differentiable species of a well-defined subgroup of the diverse Drusinae subfamily (Trichoptera, Limnephilidae). Using a 3798 bp (6 loci) molecular data set we aim to corroborate a geographically isolated new species by integrating comparative morphological studies and molecular taxonomy. CONCLUSIONS: Our results indicate that only multi-locus species delimitation provides taxonomically relevant information. The data further corroborate the new species Drusus zivici sp. nov. We provide differential diagnostic characters and describe the male, female and larva of this new species and discuss diversity patterns of Drusinae in the Balkans. We further discuss potential and significance of molecular species delimitation. Finally we argue that enhancing collaborative integrative taxonomy will accelerate assessment of global diversity and completion of reference libraries for applied fields, e.g., conservation and biomonitoring.

A hairy case: The evolution of filtering carnivorous Drusinae (Limnephilidae, Trichoptera).

The caddisfly subfamily Drusinae BANKS comprises roughly 100 species inhabiting mountain ranges in Europe, Asia Minor and the Caucasus. A 3-gene phylogeny of the subfamily previously identified three major clades that were corroborated by larval morphology and feeding ecologies: scraping grazers, omnivorous shredders and filtering carnivores. Larvae of filtering carnivores exhibit unique head capsule complexities, unknown from other caddisfly larvae. Here we assess the species-level relationships within filtering carnivores, hypothesizing that head capsule complexity is derived from simple shapes observed in the other feeding groups. We summarize the current systematics and taxonomy of the group, clarify the systematic position of Cryptothrix nebulicola, and present a larval key to filtering carnivorous Drusinae. We infer relationships of all known filtering carnivorous Drusinae and 34 additional Drusinae species using Bayesian species tree analysis and concatenated Bayesian phylogenetic analysis of 3805bp of sequence data from six gene regions (mtCOI5-P, mtCOI3-P, 16S mrDNA, CADH, WG, 28S nrDNA), morphological cladistics from 308 characters, and a total evidence analysis. All analyses support monophyly of the three feeding ecology groups but fail to fully resolve internal relationships. Within filtering carnivores, variation in head setation and frontoclypeus structure may be associated with progressive niche adaptation, with less complex species recovered at a basal position. We propose that diversification of complex setation and frontoclypeus shape represents a recent evolutionary development, hypothetically enforcing speciation and niche specificity within filtering carnivorous Drusinae.

Larval morphology and phylogenetic position of Drusus balcanicus, Drusus botosaneanui, Drusus serbicus and Drusus tenellus (Trichoptera: Limnephilidae: Drusinae).

In a recent 3-gene phylogeny of the Trichoptera subfamily Drusinae Banks, 1916 molecular data clearly correlated with the morphology and feeding ecology of larvae. The largest of three main groups, the Drusinae grazer clade, exhibits an unusual larval feeding ecology for Limnephilidae, and is the most diverse group. In this paper we describe four previously unknown Drusinae larvae from this clade: Drusus balcanicus Kumanski, 1973 (micro-endemic to Eastern Balkans); Drusus botosaneanui Kumanski, 1968 (Dinaric Western Balkans, Hellenic and Eastern Balkan, Asia Minor), Drusus serbicus Marinkovic-Gospodnetic, 1971a (micro-endemic to Dinaric Western Balkans); and Drusus tenellus (Klapálek, 1898) (Carpathians, Dinaric Eastern Balkans). Characteristically, the larvae of these species develop toothless mandibles typical for the Drusinae grazer clade. Larvae and adults were unambiguously associated by a phylogenetic approach based on two mitochondrial (mtCOI, mtLSU= 16S rDNA) and two nuclear genes (nuWG, nuCAD). In addition, information on the morphology of the larvae is given and the diagnostic features necessary for identification are illustrated.

The larvae of Stenophylax mitis McLachlan 1875 and Allogamus hilaris (McLachlan 1876a) (Trichoptera: Limnephilidae), with notes on ecology and zoogeography.

The paper gives a description of the hitherto unknown larvae of Stenophylax mitis McLachlan 1875 and Allogamus hilaris (McLachlan 1876a) (Trichoptera: Limnephilidae: Limnephilini; Vshivkova et al. 2007). Information on the morphology of the larvae is given and the most important diagnostic features are illustrated. In the context of published keys, the larva of Stenophylax mitis keys together with Stenophylax permistus McLachlan 1895, S. vibex (Curtis 1834), Stenophylax crossotus McLachlan 1884, Platyphylax frauenfeldi (Brauer, in Brauer & Löw 1857), Micropterna lateralis (Stephens 1837) and M. sequax McLachlan 1875. These species are easily separated by a combination of the following features: spatial extent of the head spinule areas, setation on femora and on the 9th abdominal dorsum, and on the number of posterior sclerites behind each lateral protuberance. Allogamus hilaris keys with Allogamus uncatus (Brauer, in Brauer & Löw 1857), A. mendax (McLachlan 1876a) and Alpopsyche ucenorum (McLachlan 1876b). These species are very similar except in head width which is < 1.50 mm in A. mendax and A. ucenorum and > 1.61 mm in A. hilaris and A. uncatus; the two species in each of the pairs are not separable. With respect to distribution, S. mitis ranges from the Iberian Peninsula to the Balkan Peninsula and from southern Italy and Greece to the Central European Highlands. Allogamus hilaris is restricted to the Western Alps and the northern half of the Apennine Peninsula. In addition, ecological characteristics are briefly discussed. 

Small-scale metapopulation structure of a limnophilic fish species in a natural river system investigated using microsatellite genotyping by amplicon sequencing (SSR-GBAS).

Habitat niches of fish species can exert a strong influence on population structure, even on a small geographical scale. In this scope, Pelasgus thesproticus is a great model species to study connectivity in riverine environments owing to its naturally patchy habitat distribution. Furthermore, it is important to conduct such studies in near-natural systems to avoid the impact of human disturbances on the river, such as fragmentation, morphological changes and habitat degradation. In this sense, the Vjosa in Albania is an excellent study area. A total of 204 individuals were sampled from five locations in the lower Vjosa and two tributaries and genotyped with 33 newly designed microsatellites loci using high throughput sequencing. The application of microsatellite genotyping by sequencing revealed genetic structure and some differentiation, even at a small spatial scale (< 65 river km). A total of 500 alleles were found with an average of 0.93 private alleles among sites with rather low FST values (< 0.04). The extent of admixture observed in some populations indicate that the genetic structure is mainly influenced by upstream populations, either from the main river itself or from tributaries. In addition, the connection between a tributary and the other sites is disrupted by the flow regime, which is reflected in a high degree of divergence from the other populations. Our results indicate that hydrological conditions of the flowing river present strong barriers to gene flow, particularly in the upstream direction, but at the same time act as dispersal corridors in the downstream direction and exhibit source-sink dynamics in which upstream populations contribute disproportionately to downstream populations for this habitat specialist along the river. It is suggested that processes of colonization and reinforcement may play an important role in shaping the genetic structure of patchily distributed fish species in natural river systems. Future studies should increase the knowledge of dispersal factors, habitat heterogeneity, consequence of source-sink dynamics, and gene flow within the system, which will help to understand and maintain important processes related to metapopulation theory and the potential evolutionary consequences of habitat loss and fragmentation.

Key and bibliography of the genera of European Trichoptera larvae.

The paper provides a synoptic key to the genera of final instar European Trichoptera larvae. The most important characters are illustrated by colour photos, with arrows highlighting the diagnostic features. A short descriptive text gives additional information for each decision and guides the reader through the determination process.

The larva of Psilopteryxpsorosa (Kolenati 1860) (Trichoptera: Limnephilidae) with notes on ecology and zoogeography.

The paper gives a description of the hitherto unknown larva of Psilopteryx psorosa (Kolenati 1860), subspecies bohemosaxonica Mey & Botosaneanu 1985 (Trichoptera: Limnephilidae: Limnephilini, Chaetopterygina; Vshivkova et al. 2007). Information on the morphology of the larva is given and the most important diagnostic features are illustrated. In the context of already available keys, the larva of P psorosa bohemosaxonica keys together with Pseudopsilopteryx zimmeri (McLachlan 1876), Chaetopteryxfusca Brauer 1857 and C. villosa (Fabricius 1798). Psilopteryxpsorosa is not yet separable from P zimmeri but may be easily separated from the two Chaetopteryx species by the median fusion of setal groups sal at the first abdominal sternum in P psorosa which is lacking in C. fusca and C. villosa. With respect to distribution, P. psorosa bohemosaxonica is present in the Bohemian Forest and the Erzgebirge (Upper Austria, Czech Republic, and Germany). In addition, ecological characteristics are briefly discussed.

The larvae of Drusus franzressli Malicky 1974 and Drusus spelaeus (Ulmer 1920) (Trichoptera: Limnephilidae: Drusinae) with notes on ecology and zoogeography.

Water quality monitoring is greatly dependent on identification tools for aquatic and semi-aquatic insects. Species-level identification improves resolution and precision of water quality assessment and requires comprehensive keys. With the aim of increasing the suitability of Drusinae for such applications, this paper gives a description of the hitherto unknown larvae of Drusus franzressli Malicky 1974 and Drusus spelaeus (Ulmer 1920). Information on the morphology of the larvae is given and the most important diagnostic features are illustrated. In the context of already available keys, the larvae of D. franzressli and D. spelaeus key together with Metanoea flavipennis (Pictet 1834), M. rhaetica Schmid 1956, D. improvisus McLachlan 1884, D. nigrescens Meyer-Dür 1875 and Ecclisopteryx malickyi Moretti 1991. These species are easily separated by differences in larval morphology (dorsal outline and sculpturing of pronotum, presence/absence of lateral gills at 2nd and 3rd abdominal segments, start of lateral fringe) and their distribution ranges. Drusus franzressli is endemic to the Hellenic western Balkans whereas D. spelaeus is endemic to the western Alps (Grenoble area). In addition, ecological characteristics are briefly discussed.

Notes on Leuctra signifera Kempny, 1899 and Leuctra austriaca Aubert, 1954 (Plecoptera: Leuctridae), with the description of a new species.

Leuctra signifera Kempny, 1899 and Leuctra austriaca Aubert, 1954 are re-described and their taxonomical status is discussed. New country records are reported for L. austriaca from Hungary and L. signifera from Italy, Slovenia, and Hungary. A new species, Leuctra papukensis sp. n., from Croatia, is described and illustrated. The subspecies Leuctra signifera jahorinensis Kacanski, 1972 is raised to species level.

New records for the Western Balkans cranefly fauna (Diptera, Tipuloidea) with the description of a new Baeoura Alexander (Diptera, Limoniidae).

The cranefly (Tipuloidea) fauna of the Western Balkans is still poorly known. In this study, occurrence data of 77 species is reported, of which two species are newly recorded for Albania, eight species for Bosnia and Herzegovina, twelve for Croatia, and seven for Slovenia, respectively. A new species, Baeouraneretvaensis Kolcsár & d'Oliveira, sp. nov. is described from Bosnia and Herzegovina, Montenegro, and Slovenia. Images of the habitus, wing, and male and female terminalia of the new species are provided. Furthermore, images of male terminalia and wings of thirteen additional species are presented.

Description of the larval stage of Drusus mixtus (Pictet, 1834) (Trichoptera: Limnephilidae: Drusinae) with notes on its ecology and zoogeography.

In the Swiss Jura adults of Drusus mixtus and unknown Drusinae larvae which could not be identified with existing keys were sampled. Based on ripe pupae, the unknown larvae were identified as D. mixtus. The association was confirmed by specimen rearing in aquaria. Based on morphology, larvae of Drusus mixtus key out together with D. croaticus in existing keys. D. mixtus is separated from the latter species by the shape of the anteromedian metanotal sclerites which are broadly triangular, whereas in D. croaticus the sclerites are almost parallel-sided, resembling a stretched rectangle. In addition, the two species are geographically well separated: D. croaticus is restricted to the confines of Croatia and Slovenia, whereas D. mixtus is only present in Switzerland and eastern France. With this present paper, all Central European Drusinae species except Drusus chapmani McL, 1901 (France, Switzerland) and D. noricus Malicky, 1981, an endemic from the Saualpe (Carinthia, Austria), are known in the larval stage.

The rare and enigmatic mayfly Prosopistoma pennigerum (Müller, 1785): Habitat characteristics, recent records from the Volga (Russia) and Vjosa (Albania) rivers, and a proposal for flagship species status.

Nymphs of all 29 described Prosopistoma species share a conspicuous synapomorphy: a round mesonotal shield, the carapace. They occur in the Palaearctic (nine species), the Oriental (12 species) and the Afrotropic as well as Australian regions (six and two species, respectively). Relatively little is known about their ecology, but past and extant distribution patterns indicate an association with undisturbed conditions. Prosopistoma pennigerum is a rare European mayfly with conspicuous nymphs. Formerly common in large rivers, it has been extirpated from central Europe over the last century.This study evaluated general habitat characteristics and human pressures for historical and current records of this rare species. Prosopistoma pennigerum is currently known from only three European rivers, all with gravel substrates, naturally dynamic discharge regimes, summer-warm water temperatures, and little human pressure.This study showed that nymphs from the Vjosa and upper Volga rivers, two relatively natural watercourses 2,000 km apart, are morphologically indistinguishable, and show no variation across a ca. 600-bp fragment of the mitochondrial cytochrome c oxidase I gene.Flagship species were first designated in the 1980s, when charismatic species with high habitat requirements such as the Bengal tiger or the giant panda, but also invertebrates are used to communicate conservation and protection needs. We propose that Europe's rarest mayfly P. pennigerum, with its unusual nymphs and remaining populations in naturally dynamic river courses, can serve as a flagship species promoting the preservation of ecological integrity in European rivers.

The coupled socio-ecohydrological evolution of river systems: Towards an integrative perspective of river systems in the 21st century.

River systems have undergone a massive transformation since the Anthropocene. The natural properties of river systems have been drastically altered and reshaped, limiting the use of management frameworks, their scientific knowledge base and their ability to provide adequate solutions for current problems and those of the future, such as climate change, biodiversity crisis and increased demands for water resources. To address these challenges, a socioecologically driven research agenda for river systems that complements current approaches is needed and proposed. The implementation of the concepts of social metabolism and the colonisation of natural systems into existing concepts can provide a new basis to analyse the coevolutionary coupling of social systems with ecological and hydrological (i.e., 'socio-ecohydrological') systems within rivers. To operationalize this research agenda, we highlight four initial core topics defined as research clusters (RCs) to address specific system properties in an integrative manner. The colonisation of natural systems by social systems is seen as a significant driver of the transformation processes in river systems. These transformation processes are influenced by connectivity (RC 1), which primarily addresses biophysical aspects and governance (RC 2), which focuses on the changes in social systems. The metabolism (RC 3) and vulnerability (RC 4) of the social and natural systems are significant aspects of the coupling of social systems and ecohydrological systems with investments, energy, resources, services and associated risks and impacts. This socio-ecohydrological research agenda complements other recent approaches, such as 'socio-ecological', 'socio-hydrological' or 'socio-geomorphological' systems, by focusing on the coupling of social systems with natural systems in rivers and thus, by viewing the socioeconomic features of river systems as being just as important as their natural characteristics. The proposed research agenda builds on interdisciplinarity and transdisciplinarity and requires the implementation of such programmes into the education of a new generation of river system scientists, managers and engineers who are aware of the transformation processes and the coupling between systems.

The larva of Plectrocnemia scruposa McLachlan 1880 (Trichoptera, Polycentropodidae.

This paper describes the previously unknown larva of Plectrocnemia scruposa McLachlan 1880. Information on the morphology of the 5th larval instar is given, and the most important diagnostic features are illustrated. In the context of existing identification keys, P. scruposa keys together with P. brevis McLachlan 1871, P. conspersa (Curtis 1834), and P. laetabilis McLachlan 1880. These species can be separated by the length of the outermost seta of the posterolateral trio on the last abdominal tergum and by presence/absence of a central pigmented mark on the posterior margin of the labrum. According to mandible morphology, the larva of this species appears to be mainly a predator and passive filter feeder of particulate organic matter.

The larva of Chaetopteryx rugulosa Kolenati 1848 (Trichoptera: Limnephilidae), with notes on ecology and zoogeography.

This paper gives a description of the hitherto unknown larva of Chaetopteryx rugulosa Kolenati 1848 (Trichoptera: Limnephilidae). Information on the morphology of the larva is given, and the most important diagnostic features are figured. In the context of the known European Chaetopterygini and Stenophylacini species, the larva of C. rugulosa can be separated from morphologically close species by metanotal sclerite morphology, setation, the extension of the lateral fringe, and by case morphology.

A new Drusinae species from the western Alps with comments on the subfamily and an updated key to filtering carnivore larvae of Drusinae species (Insecta: Trichoptera: Limnephilidae).

A new Drusinae species, Drusus katagelastos sp. nov., of the Drusus chapmani Species Complex, is described based on a male and associated larvae. Adult-larval association was achieved through DNA barcoding. The male of the new species differ from that of its congeners in the formation of the intermediate appendages and parameres. Information on the morphology of the larva is given, and important diagnostic features are discussed. In the context of filtering carnivore Drusinae, the larva of the new species can be separated from other filtering carnivore species by the dense cover of long translucent bristles within the frontal cavity surrounded by a circular corona of long bristles. Drusus katagelastos sp. nov. is known from only northwestern Italy (Piemonte).

Impacts of multiple stressors on freshwater biota across spatial scales and ecosystems.

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors. For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response variable. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions.