A global synthesis of microplastic contamination in wild fish species: Challenges for conservation, implications for sustainability of wild fish stocks and future directions.

Research on the occurrence of microplastics in wild fish populations is a constantly growing area, requiring continuous reviews to properly keep up with the fast pace of publications and guide future work. This review analyses the scientific output of 260 field studies covering 1053 different fish taxa for the presence of microplastics. To date, microplastics have been recorded in 830 wild fish species, including 606 species of interest to commercial and subsistence fisheries. Among these, based on IUCN Red List status, 34 species are globally classified in one of the three threatened categories (Critically Endangered, Endangered or Vulnerable) and another 22 species were assessed as "Near Threatened". Of the species for which the IUCN Red List tracks population trend data, the fish species reported to have microplastics so far include 81 which are recorded as declining, 134 as stable and just 16 as increasing. This review highlights the potential implications of fish microplastic contamination to biodiversity conservation, sustainability of wild fish stocks, and human food safety and security. Finally, recommendations for future research are presented.

Effects of reservoir cascades on diversity, distribution, and abundance of fish assemblages in three Neotropical basins.

River systems are characterized by the existence of longitudinal processes structuring fish assemblages. However, the construction of dams, many of them built in cascades, are disrupting these processes worldwide. Here, we analyzed the fish assemblages across reservoir cascades in three Brazilian river basins (Iguaçu, Paranapanema, and São Francisco) to identify whether there is a spatial convergent pattern and to infer the mechanisms structuring metacommunities in these Neotropical rivers. Linear models were used to assess the effect of reservoir cascades, and the associated morphological, spatial and environmental variables, on the species richness and diversity along them. We analyzed if reservoir cascades produce similar species distribution patterns using the elements of metacommunity structure framework and beta diversity and its components. Finally, super-organizing maps were used to find common trends in species abundances and the environmental, morphological, and spatial variables along cascades. The negative relationship between species richness and diversity and the position in the cascade indicated diversity declines along cascades. However, the resulting metacommunities varied in each river basin. They conformed a quasi-Gleasonian structure, a Clementsian structure, and a nested structure with stochastic species loss in the Iguaçu, Paranapanema, and São Francisco River basins, respectively. Generally, total beta-diversity (ßsor) and species turnover (ßsim) between pairs of reservoirs increased along reservoir cascades, especially at the downstream end, whereas nestedness (ßsne) depicted distinct trends in each river basin. By contrast, there were general decreases in species abundances along cascades, especially downstream the fourth reservoir, with very few species benefiting from such situation. In general, species present in the downstream reservoirs were subsets of the species present in the upstream reservoirs (particularly in the São Francisco River Basin), while some had singular responses to the environmental gradient and appeared or disappeared at random. Although the cascade has an effect on fish assemblages, reservoir characteristics and operation also influence them. Our study highlights the impact of such structures and shows general patterns of fish assemblages that should help to mitigate the resulting ecological impacts and assist the process of infrastructure planning.