Abstract
Seasonal variation in the vertical distribution in chlorophyll（Chl.）fluorescence was investigated to clarify the characteristics on primary production in East-Hiuchi-Nada, Seto Inland Sea. We made observations of three size-fractionated concentrations of Chl. a（＞20μm, 8－20μm, ＜8μm）, species composition of phytoplankton community, and nutrient concentrations. The maximum Chl. fluorescence was observed in the bottom layer from April to June and September and in the subsurface layer in July and August. Size-fractionated Chl. a concentrations showed that a higher rate in the＞20μm fraction was observed when Chl. a concentrations were high. The euphotic layer reached the bottom in this area because transparency was high in the stratification period except for in July. These findings could be related to the Chl. maximum in the bottom layer when the stratification was developed. It was considered that the primary production in this area could be supported by sufficient light conditions, nutrients
supply by release from the sediment, and intrusion of nutrient-rich water from Bisan-Seto.
