Study of Limiting Nutrient and Size Structure of Phytoplankton Community in Western Seto Inland Sea and Pacific Ocean.

Horizontal variations of limiting nutrient and size structure of phytoplankton community at estuarine and oceanic stations from Hiroshima Bay to the Pacific Ocean were studied. The following results were obtained :1) Concentrations of DIN, DIP and chlorophyll a were very high in Hiroshima Bay estuary and decreased toward the south sea area.2) Limiting nutrient of phytoplankton in the Hiroshima Bay estuary was estimated to be phosphorus, whereas that in other stations was estimated to be nitrogen.3) Nanophytoplankton dominated total biomass of phytoplankton population in terms of chlorophyll a in Hiroshima Bay. On the contrary, picophytoplankton showed the greatest fraction of total biomass of phytoplankton population in terms of chlorophyll a from the Sea of Iyo to the Pacific Ocean.4) Cell density of picocyanobacteria was maximum in the Hiroshima Bay estuary, but the lowest was observed in southernmost station of the Pacific Ocean.