A series of enclosed ecosystem experiments were conducted in a land based tank near the seaside of West Xiamen Harbor.The results of experiments conducted in different seasons and years showed a repeatble phytoplankton succession. In this relatively stable ecosystem with added nutrients and trace metals,diatoms dominated initially,dinoflagellates dominated in the later stage,and dinoflagellate red tides eventually occurred.Vitamin B 12 enrichment may speed up this succession process. Stirring the water column could stop this process. Soluble Mn at a level of 3-4 μg/L in seawater,which also is the existing concentration of solu ble Mn in Xiamen Harbor seawater,is sufficient for the multiplication of algae and occurrence of red tide.The present study showed that excessive soluble Mn in Xiamen Harbor cannot cause red tide,and that Fe was one of the important factors causing diatom red tide in this present study.. A series of enclosed ecosystem experiments conducted in a land based tank near the seaside of West Xiamen Harbor. The results of the experiments conducted in different seasons and years showed a repeatble phytoplankton succession. In this relatively stable ecosystem with added nutrients and trace metals, diatoms Dominated initially, dinoflagellates dominated in the later stage, and dinoflagellate red ttings due occurred process. Vitamin B 12 enrichment may speed up this succession process. Stirring the water column could stop this process. Soluble Mn at a level of 3-4 μg / L in seawater, which also is the existing concentration of solu ble Mn in Xiamen Harbor seawater, is sufficient for the multiplication of algae and occurrence of red tide. the present study showed that excessive soluble Mn in Xiamen Harbor can not cause red tide, and that Fe was one of the important factors causing diatom red tide in this present study ..