Long-Term Variations in Chlorophyllaand Primary Productivity in Jiaozhou Bay, China

Based on long-term data of measurements of nutrient and chlorophyllaconcentrations as well as estimates of primary production, the response of phytoplankton to nutrient enrichment was evaluated in the highly urbanized Jiaozhou Bay. Results showed that phytoplankton biomass, as indicated by chlorophyllaconcentration, did not show a direct linear response to increased nutrient concentrations. Instead, chlorophyllaconcentration was maintained at a constant level in the last two decades in Jiaozhou Bay, so did primary productivity. However, a reduction of zooplankton biomass was observed during the same period. Analysis showed that although the scale of phytoplankton blooms might be limited by availability of silicate due to low Si/N ratio and low concentration, top-down control on phytoplankton biomass by bivalve grazing may be an important factor in Jiaozhou Bay ecosystem.