Distribution of Benthic Microcystis Cells as Potential Source of Algal Blooms in Lake Hachiro

摘要

Harmful algal blooms occur annually in Lake Hachiro located Akita Prefecture, Japan. We investigated the distribution of Microcystis cells in the bottom sediment of Lake Hachiro because recruitment of Microcystis cells from bottom sediment to water column may contribute to occurrence of algal blooms. The sediment samples were collected from 31 sites before the occurrence (on 22 June, 2016) and after the decline of algal blooms (on 7 November, 2016). Epifluorescence microscopy of sediment samples revealed that a large number of Microcystis cells were detected from the same sites in June (<8.4×10~7 cells/g-dry) and November (<1.4×10~8 cells/g-dry). This result suggested that Microcystis cells were tended to accumulate on the same sites. Since cell density was 1-order higher in November than in June, Microcystis living cells seemed to precipitate bottom surface after the decline of algal blooms. As a part of these accumulated cells were confirmed to be alive by rRNA analysis, they may contribute to the occurrence of algal blooms in the next season.