Seasonal Changes in Size-Fractionated Primary Production and Nutrient Concentrations in the Temperate Neritic Water of Funka Bay, Japan

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Size-fractionated primary productivity and chlorophyllaconcentration were studied at two stations in the temperate neritic waterof Funka Bay, Japan, from April 1984 to May 1985. Size distributions of phytoplankton were discussed in relation to nutrient availability. In the central part of the bay, 66% of the annual primary production occurred during the spring phytoplankton bloom with 95% of the spring production being accounted for by thegreater than 10μm size fraction, which was dominated by diatoms. The increase in this large fraction was enhanced at both stations when nutrient concentrations increased in the bay's upper layer. Under low nutrient concentrations during summer, small phytoplankters (<2μm) accounted for 40 to 75%(average 60%) of the total14C uptake atthe central station, and from 25 to 59%(average, 45%) at the coastal station. However, a sudden nutrient enrichment at the coastal station during the summer triggered the growth of the large size fraction. These seasonal and regional changes in total14C uptake were attributed to the large size fraction, composed mainly of diatoms. From the decreases in various nutrients during diatom blooms, it was further suggested that the predominance of diatoms was determined, not only by nutrient concentrations, but also by their relative availability.
日本海洋学会の論文