Seasonal changes in Skeletonema species in the sediment of Tokyo Bay evaluated with real-time PCR assays

Abstract

To investigate seasonal changes in the abundance and species composition of Skeletonema cells in the innermost area of Tokyo Bay, we examined the species composition of Skeletonema in the surface sediment using real-time PCR and enumerated the resting cell density by the MPN method. The process of the decrease in Skeletonema cells in the sediment was also investigated using incubation experiments. Six species of Skeletonema (S. ardens, S. costatum s.s., S. japonicum, the S. marinoi–dohrnii complex, S. menzelii, and S. potamos) were detected in the sediment. The light intensity at the bottom, estimated based on the Secchi depth, was very low, suggesting that the possibility of Skeletonema rejuvenation was not high for most of the year. In the incubation experiment, the cell density of Skeletonema decreased by 40% on average after 30 days of incubation. In August and October 2019, S. potamos was the only species to be detected in the water column; however, its cell density in the sediment remained quite low (<10³ cells g⁻¹). The result suggests that not all sinking Skeletonema cells form resting cells, and the resting cell formation differed among the species.