Permalink : http://hdl.handle.net/2115/47535

KEYWORDS : Phytoplankton;Diatom bloom;Nitrogen depletion;Harima-Nada

　In the eastern Seto Inland Sea, dissolved inorganic nitrogen has decreased due to the reduction of nutrient inputs, and there have been changes in the total cell density and the composition of the phytoplankton assemblages. The major phytoplankton component was diatoms, and the contribution was always over 90 percent of total phytoplankton since the 1990s. In order to elucidate growth characteristics and nutrient consumption of diatom species, we conducted major nutrients-enrichment bottle incubation experiments on shipboard using the surface waters in Harima-Nada, eastern part of the Seto Inland Sea. Seawater incubation experiments demonstrated that nutrient environments for phytoplankton are in a state of nitrogen-limitation in Harima-Nada. The addition of nitrate to surface waters of this coastal region promotes blooms of large chain-forming diatom species. These results suggest that diatom blooms cause depletion of the nutrients (mainly nitrogen) in Harima-Nada.