Relationships between the dominant phytoplankton and DIN:DIP ratios in Osaka Bay and Harima-nada

Abstract

The relationships between the dominant phytoplankton and the water quality factors were examined at seven stations in Osaka Bay and Harima-nada (1995-1996). Monthly changes of water quality factors in Osaka Bay and Harima-nada showed that DIN (dissolved inorganic nitrogen) : DIP (dissolved inorganic phosphorus) and TP (total phosphorus) : DIP ratios were high in May and June, while DIN:DIP ratio was low and TN (total nitrogen): DIN ratio was high in August and September. The relationships between the dominant phytoplankton and the water quality factors were considerably variable and complex. Skeletonema costatum, Pseudonitzschia spp., Rhizosolenia fragilissima, and Eucampia zodiaus occurred in waters with high DIN : DIP ratio (>100), Ceratium furca, Noctiluca scintillans, Prorocentrum micans, Leplocylindrus danicus, Gyrodinium spirale, Mesodinium rubruon, and Prorocentrum triestinum did with moderate DIN:DIP ratio, and Gymnodinium mikimotoi, Rhizosoknia setigera, Chaetoceros curvisetum, and C. affinis did with low DIN:DIP ratio (<10). DIN :DIP ratio in waters where dominant phytoplankton occurred increased with increased TN x TP, TN:TP, and TP:DIP ratios, whereas it did not decrease with increased TN:DIN ratio.