The goal of this study is to demonstrate a hypothesis that phytoplanktonic intracellular organic matters released by cell disruption caused during predation and extracellular organic matters contained in exudate have distinct effects on coastal prokaryotic community. Coastal prokaryotic community collected in Osaka bay was cultured with addition of intracellular or extracellular organic matters extracted from Heterosigma akashiwo (NIES 293 strain), or f divided medium for control. Each triplicated flask was incubated at 20 degree Celsius with a 10 h 14 h light photocycle. Samples were taken on the day 1, 3, 5, 7, 9, 11, and 13 during incubation. DNA extracted from each samples were offered for 16S rRNA (V3 V4 region) analysis.