Germination of phytoplankton resting cells in surface sediments collected from the tributary and littoral zones of Lake Taihu, China

Phytoplankton responsible for harmful algal blooms (HABs) may originate from the seed bank present in lake and river sediments. In this study, we investigated the germination of phytoplankton in the laboratory from resting cells in sediments collected during spring from four tributary and littoral zones of Lake Taihu (east, south, west, and north), the season before HABs typically occur. We evaluated the potential for germinated phytoplankton to contribute to HABs. We found that 26 species from three phyla including Cyanobacteria, Bacillariophyta, and Chlorophyta germinated from the sediment during the 15-day incubation experiment. The germinated phytoplankton species from the sediments collected in most areas were moderately or very similar, but dominant species exhibited different temporal and spatial distributions. The densities of germinated cells for different phytoplankton species varied at different times during the incubation period. Cyanobacteria Microcystis spp. (1,511 cells g⁻¹ wet weight) and Bacillariophyta Melosira sp. (2,865 cells g⁻¹ wet weight) had the highest cell densities after 10-day incubation, whereas Chlorophyta had the highest cell density (54 cells g⁻¹ wet weight) after 15-day incubation. There was a high number of Cyanobacteria resting cells that could germinate from the seed bank preserved in the sediments, suggesting potential risks of HABs throughout Lake Taihu.