Temporal patterns in silica deposition among siliceous plankton during the spring bloom in the Oyashio region

Bottle incubations were conducted to investigate silica deposition and growth characteristics of siliceous phytoplankton in the Oyashio region using PDMPO, 2-(4-pyridyl)-5-((4-(2-dimethylaminoethyl-aminocarbamoyl)-methoxy)phenyl)oxazole, a fluorescence probe. This stain shows clear fluorescence in the position of newly produced silica cell walls during their vegetative cell growth. Parmales and diatoms dominated siliceous phytoplankton during the pre-bloom and bloom periods, and were successfully stained with PDMPO, indicating active silica deposition. Low PDMPO labeling of cells of the dominant diatoms relative to their initial abundance was often observed in the later half of the bloom period compared with high PDMPO labeling early in the bloom. That suggests that diatom silica deposition had slowed. Silica deposition in other siliceous plankton, i.e. silicoflagellates and choanoflagellates, and diatom resting spores was also detected. Our results show that the PDMPO technique is appropriate to demonstrate important biological processes in the silicon and carbon biogeochemical and cycles in the Oyashio region.