First Record of (Bacillariophyceae) from Khalaktyrskoye Lake (Kamchatka)

A new finding of the diatom Grunow, 1880 in Khalaktyrskoye Lake (Kamchatka) during the period of its mass growth in April 2023 is described. Density of this species was 4.95 million cells/l or 92.6% of the total density. A list of 45 species of associated diatoms is provided. According to electron microscopy data, it was established that the population of was represented by two morphotypes – and , differing in quantitative (number of areolae and rows of areolae in 10 μm) and qualitative (shape of spines, location and shape of areolae on the valve face) characteristics. Features in the shape of the areolae and their location for different frustules of the morphotype have also been identified. Mass growth of this species and noted morphological features of its frustule structure could be due to the high level of eutrophication of the Khalaktyrskoye Lake.