Variability of the biomass, chemical composition and productivity of phytoplankton in Kinu-ura Bay, Japan during the rainy season

Abstract

At intervals from 1 to 5 days, biomass, chemical composition and production rate of phytoplankton populations and physicochemical environmental parameters were measured in Kinu-ura Bay, Japan, a semi-closed eutrophic bay, during the rainy season from late May to early July 1983. Considerable concentrations of inorganic nutrients, probably derived from increased river influx from the land due to rainfall, were frequently introduced into the surface water of the bay during the experimental period. This influx from the rivers appeared to be one of the most important sources of inorganic nutrients supplied to phytoplankton blooms during this season. The particulate protein/carbohydrate ratio at the surface water was generally ≥3, indicating sufficient nutrients for high phytoplankton growth at the surface throughout this season. The average daily production rate during the experimental period, determined with the 13C method, was 2·2 g C m−2 day−1 and consequently, daily particulate organic nitrogen production rate was assumed to be 0·37 g N m−2 day−1. Estimated nitrogen supply was enough for primary production during the experimental period, consistent with the result that chemical composition of particulate organic matter indicated no nitrogen limitation.