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.

Invasion of Corbicula fluminea (Müller, 1774) (Bivalvia: Corbiculidae) in water bodies from the East Aegean River Basin in Bulgaria

Two decades after the first record of the invasive mussel Corbicula fluminea (Müller, 1774) in Bulgaria in 2001, it has been found in many surface lotic and standing waters in the Bulgarian Danube River Basin. The aim of the current study is to report the finding of C. fluminea in lotic environment of the East Aegean water basin in Bulgaria. Six new localities of the mussel, all situated in the lower stretches of the Tundzha (two) and Maritsa (four) River were registered. The distributional patterns of the mussel and the abundance of its populations in relation to the environmental conditions were analyzed. The adaptive character of the Corbicula, the possible path for invasion as well as the probability of rapid spread of the mussel in the largest rivers and their tributary systems in south-eastern part of Balkan Peninsula was discussed.