Latest data on the hydrophysical and biological state of the residual basins of the Aral Sea are presented and compared. Direct, quasi-simultaneous observations were carried out in the central part of the Western Large Aral Sea, the northern extremity of the Large Aral known as Chernyshev Bay, Lake Tshchebas, and the Small Aral Sea in October 2014. The Large Aral Sea and Lake Tshchebas transformed into hyperhaline water bodies with highly special taxocene structure. The Small Aral Sea was a relatively diverse brackish ecosystem, which was rather similar to the pre-desiccation environment. The Small Aral Sea and Lake Tshchebas exhibited a fully-mixed vertical structure, whereas the Western Large Aral Sea was strongly stratified. Our data show that during desiccation, different parts of the Aral Sea experienced different environmental conditions, resulting in qualitative and quantitative differences in the physical and biological regimes among the different residual basins.

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A survey of publications and collections databases reveals a pattern of non-indigenous decapods distribution in the 13 seas around Russia and adjacent countries. No alien species were reported from Russian territorial waters and exclusive economic zone in the Japan, Okhotsk, west Bering and most of the Siberian shelf Seas. From the seas and their basins in East Europe, 13 alien species have been recorded, with seven of these yet to become established. Established or commonly occurring species can be categorized as: ‘global invaders’ (Chinese mitten crab,Eriocheir sinensisin the White, Baltic, Black, Azov and Caspian Seas; and Harris mud crab,Rhithropanopeus harrisiiin all mentioned seas, except the White Sea); ‘regional aliens’ (Palaemon adspersusandP. elegansin the Caspian Sea and the latter species in the Baltic); and ‘Arctic invaders’ (Kamchatka king crabParalithodes camtschaticusand snow crabChionoecetes opilio).Eriocheir sinensisis the most widely occurring alien decapod species, but there are no indications of an established population in East Europe. For this and other mentioned crab species, invasion history, distribution and important biological data are reviewed. In the seas where few or no native crab species have been present, Harris mud crab (in the Azov and Caspian Seas), Kamchatka crab (in the Barents Sea) and snow crab (in the Barents and Kara Seas) have shown rapid establishment (within two decades) of an invasive population throughout an entire basis or its significant part.

Expanding human activities alongside climate change, the introduction of invasive species and water contamination pose multiple threats to the unique marine ecosystems of the Pechora Sea in the Russian Arctic. Baseline data on biodiversity and responses to environmental change are urgently needed. Benthic decapod crustaceans are globally distributed and play an important role in fisheries, yet their roles in food webs are less understood. In this study, we used an integrated approach combining stomach content analysis and stable isotope analyses (δ13C and δ15N) to examine the trophic niches of three decapod species in the Pechora Sea including the invasive snow crab Chionoecetes opilio and two species of native decapods, the spider crab Hyas araneus and the hermit crab Pagurus pubescens. Stomach contents of 75 decapods were analysed (C. opilion = 23; H. araneusn = 9; P. pubescensn = 43), and 20 categories of prey items were identified with the most frequently occurring prey items being bivalve molluscs (Ciliatocardium ciliatum, Ennucula tenuis, Macoma calcarea), polychaetes, crustaceans and plant debris. Bayesian ellipse analyses of stable isotope signatures (n = 40) revealed that C. opilio displays an overlapping trophic niche with the two native decapods, providing direct evidence that the invader likely competes for food resources with both H. araneus and P. pubescens. As such, the presence of this invasive species could hold important consequences for trophic interactions, benthic ecosystem functioning and biodiversity. Microplastics were also found to be a likely stressor on this ecosystem, as 28% of all stomachs contained digested microplastics among other items. Long-term studies of benthic ecosystem structure and functioning are now needed to more fully understand the extent to which this new competitor may alter the future biodiversity of the Pechora Sea alongside the additional stressor of digested plastics.