Allelopathic interactions between the red-tide causative dinoflagellate Prorocentrum donghaiense and the diatom Phaeodactylum tricornutum This study was supported by the Natural Science Foundation of China-Guangdong Province Joint Key Project (U1133003) Science Technology Planning Project of Guangdong Province (2012B020307009) Open Fund from Key Laboratory of Aquatic Eutrophication Control of Harmful Algal Blooms of Guangdong Higher Education Institutes Open Fund from Key Laboratory of Microbial

The interactions between the red-tide causing dinoflagellate Prorocentrum donghaiense and the marine diatom Phaeodactylum tricornutum were investigated using a co-culture experiment and an enriched culture filtrate experiment. The results showed that when the two microalgae were cultured together with different initial cell densities, the growth of one species was basically suppressed by the other one. In addition, the enriched culture filtrates of one species had generally inhibitory effects on the other one. Our result inferred that P. donghaiense and P. tricornutum would interfere with each other mainly by releasing allelochemicals into the culture medium, and that the degree of allelopathic effects was dependent on the initial cell densities and growth phases. The allelopathic interactions between microalgal species may contribute to the formation and succession of red tides.