Analysis of the Amphipod Fauna of Continental Water Bodies in the Northwestern European Part of Russia

The faunal composition of Amphipoda crustaceans of continental water bodies in northwestern Russia is analyzed. To compile a checklist of amphipod species, data from original collections made in 1998–2021, the collections of the Zoological Institute, and published information are used. To date, 29 species of amphipods have been recorded from the continental waters of the region. An arealogical analysis of the faunal composition reveals six groups or distribution patterns: Holarctic, West Palearctic, and North Atlantic estuaries, and further three groups of emigrants (settlers) from the Baikal–Siberian, Ponto-Caspian, and Arctic regions. The greatest species richness is recorded in estuarine sections of Baltic Sea rivers on the territories of Leningrad and Kaliningrad oblasts, as well as freshwater bodies of the Republic of Karelia. In terms of species richness, estuarine species amphi-Atlantic in distribution and representatives of allochthonous elements of fauna (invasive species) from the Ponto-Caspian basin dominate in the region. The most common in the region are representatives of Holarctic and Palearctic complexes, as well as species of Arctic and Baikal–Siberian origins. Among them, the following species are most often be recorded in lakes: Gammarus lacustris, Monoporeia affinis, Palaseopsis quadrispinosa, and Gmelinoides fasciatus, compared to G. zaddachi, G. oceanicus, G. tigrinus, and Pontogammarus robustoides in estuarine brackish waters. Human-mediated introductions, both intentional and accidental, must have facilitated the appearance of invasive species in the fauna of northwestern Russia. In the future, an increase in species richness in the region can be expected to occur in two ways: through the introduction of marine species into freshwater and due to speciation.