Seven Epithemia taxa (Bacillariophyta) from Lake Akan (Japan) and their salinity tolerances

The ecologies (salinity tolerance) of many diatoms are largely unknown, despite their potential to contribute to more detailed paleoenvironmental reconstructions. This study therefore aimed to investigate the relationship between diatom species and salinity. We cultured seven cosmopolitan benthic diatom species obtained from Lake Akan, a freshwater inland lake in Japan: Epithemiaadnata, E.frickei, E.gibba, E.operculata, E.sorex, E. sp. and E.turgida. Each species was cultured at eleven salinities between 0‰ and 50‰. Epithemiaadnata, E.frickei and E.sorex had the highest growth rate at a salinity of 3‰, with no further increase observed above 25‰. However, E.gibba had the highest growth rate at a salinity of 5‰, with no increase at salinities ≥ 30‰. These results suggest that E.adnata, E.frickei, E.gibba, and E.sorex grow in freshwater to brackish-water environments. Epithemiaoperculata and E. sp. proliferated at all salinities, indicating that they can adapt to hypersaline environments. However, E.turgida did not survive in salinities >10‰, making it the species with the narrowest salinity tolerance range. These results provide new knowledge that improves the understanding of the ecology of these species in modern environments and offer insights into paleoenvironmental reconstructions through diatom analysis.