Taxonomic Composition of Protist Communities in the Coastal Stratified Lake Kislo-Sladkoe (Kandalaksha Bay, White Sea) Revealed by Microscopy

Lake Kislo-Sladkoe is a stratified water body partly isolated from the White Sea. Perennial meromixis in lake irregularly alternates with mixing events. Taking into account that protists of Arctic coastal bodies are understudied, we evaluated for first time vertical structure, species richness, and diversity assigned to different taxonomic groups using light, luminescent, scanning electron microscopy. To test research hypothesis event affects stratification composition lake, compared protist communities two extremely states: strong vs. full mixing. A total 97 morphologically distinct phototrophic, heterotrophic, mixotrophic were revealed most diverse supertaxa SAR (59), Obazoa (9), Excavates (14). The hidden (43 species) was bit less than active (54 species). list micrographs cells observed provided. majority cosmopolitan or widespread northern sea waters. patterns absolutely 2018 2021. In July 2018, clearly inhabited layers lake. Bloom cryptophyte Rhodomonas cf. baltica detected chemocline, whereas maximum density its grazers adjacent layers, mainly dinoflagellates Gymnodinium sp. Scrippsiella trochoidea, as well ciliate Prorodon 2021 due recent seawater, there no column except superficial 0–1 m layer fresh water.