| Summary: | Searching for regularities in the species composition and diversity of scaled chrysophytes is crucial formonitoring Arctic waterswithin the concept of global climate change since these organisms are goodindicators of environmental changes. Transmission electron microscopy allowed us to investigate thespecies diversity of scaled chrysophytes in 14 Arctic water bodies near the town of Tiksi (Yakutia) relativeto hydrochemical gradients. We described a high species richness of scaled chrysophytes, 65 speciesfrom 6 genera: Chrysosphaerella (2), Paraphysomonas (8), Lepidochromonas (3), Spiniferomonas(10), Mallomonas (23), Synura (19). The water bodies we studied had a significantly different speciescomposition. The composition of the species in the study area was confirmed to be affected by concentrationsof water dissolved oxygen (O2), ion nitrate (NO3-) and copper ion (Cu2+) as well as by indicatorsof biological and chemical oxygen demand (BOD and COD). The species richness (α richness) isproved to be higher within creasing concentrations of COD and O2, while increasing concentrations ofcopper ions (Cu2+) in water led to its reduction. According to ecological and biogeographic data, ubiquitousand cosmopolitan species prevailed in the longitudinal group of the study area (60 %), whilepolyzonal species (55 %) predominated in the latitudinal group. A high share of Arctic boreal species(19 %) and the presence of typically boreal species (11 %) were identified in the latitudinal group. Abiogeographical distribution of scaledchrysophytes typical of Arctic water bodies in contemporary conditions that reflect global warming trends was described. This study was performed using the facilities of the Instrumentation Center for Electron Microscopy at the Integrated Center of Ultramicroanalysis (Limnological Institute, Siberian Branch, Russian Academy of Sciences. The study was supported by the projects No. 0279-2021-0008 (Limnological Institute) and No. 0297-2021-0023 (Institute for Biological Problems of Cryolithozone).
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