Multi-decadal improvements in the ecological quality of European rivers are not consistently reflected in biodiversity metrics.

Humans impact terrestrial, marine and freshwater ecosystems, yet many broad-scale studies have found no systematic, negative biodiversity changes (for example, decreasing abundance or taxon richness). Here we show that mixed biodiversity responses may arise because community metrics show variable responses to anthropogenic impacts across broad spatial scales. We first quantified temporal trends in anthropogenic impacts for 1,365 riverine invertebrate communities from 23 European countries, based on similarity to least-impacted reference communities. Reference comparisons provide necessary, but often missing, baselines for evaluating whether communities are negatively impacted or have improved (less or more similar, respectively). We then determined whether changing impacts were consistently reflected in metrics of community abundance, taxon richness, evenness and composition. Invertebrate communities improved, that is, became more similar to reference conditions, from 1992 until the 2010s, after which improvements plateaued. Improvements were generally reflected by higher taxon richness, providing evidence that certain community metrics can broadly indicate anthropogenic impacts. However, richness responses were highly variable among sites, and we found no consistent responses in community abundance, evenness or composition. These findings suggest that, without sufficient data and careful metric selection, many common community metrics cannot reliably reflect anthropogenic impacts, helping explain the prevalence of mixed biodiversity trends.

Long-term trends in crayfish invasions across European rivers.

Europe has experienced a substantial increase in non-indigenous crayfish species (NICS) since the mid-20th century due to their extensive use in fisheries, aquaculture and, more recently, pet trade. Despite relatively long invasion histories of some NICS and negative impacts on biodiversity and ecosystem functioning, large spatio-temporal analyses of their occurrences are lacking. Here, we used a large freshwater macroinvertebrate database to evaluate what information on NICS can be obtained from widely applied biomonitoring approaches and how usable such data is for descriptions of trends in identified NICS species. We found 160 time-series containing NICS between 1983 and 2019, to infer temporal patterns and environmental drivers of species and region-specific trends. Using a combination of meta-regression and generalized linear models, we found no significant temporal trend for the abundance of any species (Procambarus clarkii, Pacifastacus leniusculus or Faxonius limosus) at the European scale, but identified species-specific predictors of abundances. While analysis of the spatial range expansion of NICS was positive (i.e. increasing spread) in England and negative (significant retreat) in northern Spain, no trend was detected in Hungary and the Dutch-German-Luxembourg region. The average invasion velocity varied among countries, ranging from 30 km/year in England to 90 km/year in Hungary. The average invasion velocity gradually decreased over time in the long term, with declines being fastest in the Dutch-German-Luxembourg region, and much slower in England. Considering that NICS pose a substantial threat to aquatic biodiversity across Europe, our study highlights the utility and importance of collecting high resolution (i.e. annual) biomonitoring data using a sampling protocol that is able to estimate crayfish abundance, enabling a more profound understanding of NICS impacts on 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.

Influence of thermal regime and land use on benthic invertebrate communities inhabiting headwater streams exposed to contrasted shading.

Headwaters account for a high proportion of total freshwater stream-channel length in a drainage basin and are critical habitats for rare, endangered, and specialized species. In the context of climate warming, increasing water temperatures may be an ultimate threat to cold-adapted species even in temperate ecosystems. Climate change effects on streams may interact with other pressures such as pollution or habitat fragmentation, confounding their real impact on biological communities. Three headwater streams exposed to contrasted shading and land use conditions were sampled over a three-year period in spring and autumn (2010-2012). Five stations distributed along the longitudinal continuum were chosen in the upstream part of each stream. In addition to benthic invertebrate sampling, water temperature was recorded continuously using data loggers. Results showed that the riparian woodland associated with forested land use throughout the catchment clearly moderated winter temperature minima, summer temperature maxima and thermal variability compared to open river channels with narrow or absent riparian tree cover. Although, the variability in macroinvertebrate species distribution was mainly attributed to anthropogenic land use in the catchment, a significant part of the variability was explained by temperature descriptors such as the number of cumulative degree-days in summer and extremes in winter temperature. Trichoptera species preferring headwaters and cold water temperatures were found exclusively in the forested unimpacted stream. Conservation issues are discussed in relation to the predicted loss of the potential future distributions of these Trichoptera cold-adapted species.

Identification and mRNA expression of pi-class glutathione S-transferase and selenium-dependent glutathione peroxidase in the gudgeon Gobio gobio exposed to PCB 77.

In aquatic environments some pollutants are present in water and sediments and organisms possess cellular detoxification systems to face up these xenobiotics. The gudgeon, Gobio gobio, is a freshwater benthopelagic fish that appears particularly adequate for an ecotoxicological assessment of rivers. The aim of this study was the identification of GST and GPx genes in this organism in order to develop new indicators of early exposure to xenobiotics in aquatic environments. Reverse-transcription PCR using degenerate primers and RACE-PCR allowed us to identify a selenium-dependent glutathione peroxidase (Se-GPx), belonging to the class one (GPx-1), and a pi-class glutathione S-transferase (pi-GST) cDNAs. These sequences encoded for 191 and 208 amino acids proteins respectively, they exhibit high identities and similarities with corresponding proteins in other fish and the residues essential to the enzymatic functions are highly conserved. The expression patterns of these two mRNA were established by real-time PCR in five gudgeon tissues: liver, gills, kidney, spleen and muscle. The mRNA levels of these genes were highest in the liver and their expression in the other tissues exhibited some differences. Gudgeons exposed to PCB 77 in the food exhibited an increase in pi-GST mRNA and a decrease in GPx-1 transcripts levels in the liver. However, no modification of the enzymatic activities was observed. The present study provides the first transcriptional data regarding pi-GST and GPx-1 in the gudgeon Gobio gobio.

Chemical contaminants in fish species from rivers in the North of Luxembourg: Potential impact on the Eurasian otter (Lutra lutra).

Contamination levels of PCBs, and of the heavy metals cadmium (Cd), lead (Pb) and mercury (Hg) were analyzed in four fish species from seven rivers in the North of Luxembourg. During August and September 2007, 85 samples of fish were collected belonging to four species: the stone loach (Barbatula barbatula, n=12 pools), the chub (Squalius cephalus, n=36), the barbel (Barbus barbus, n=23) and eel (Anguilla anguilla, n=14). The concentration of seven indicator PCBs ( summation operator(7)PCBs) reached a mean of 39ngg(-1) and varied between 4.0 and 346.2ngg(-1) (wet wt) depending on the site and species. Fish collected at Wallendorf on the Our River and sites on the Wiltz and the Clerve rivers showed the highest concentrations for PCBs. In comparison with 1994, PCB levels in fish decreased strongly during the last decade in these rivers. Lead was detected at low levels (0-181.4ngg(-1) wet wt). Mercury concentrations ranged between 10.3 and 534.5ngg(-1) (wet wt) exceeding maximum tolerable levels for human consumption of 500ngg(-1) in two fish out of 85. Chubs and eels from the Sûre River were the most contaminated by mercury. Cadmium levels varied between 4.0 and 103.9ngg(-1) (wet wt). In addition to mercury in fish, cadmium was the most problematic pollutant on the Our, the Wiltz, the Clerve and the Troine Rivers, because values found in 20% of fish exceeded the threshold of about 10-50ngg(-1) (wet wt) recommended for human health. The total PCB level predicted to accumulate in livers from otter potentially feeding on these fish based on a previously published mathematical model is 37.7microgg(-1) (lipid wt), which is between a proposed "safe level" and a "critical level" for otters. Rivers in the North of Luxembourg are thus to some extent polluted, and the establishment of otter populations could be affected by current levels of contamination.