The inhibitory effects of seaweed Gracilaria lemaneiformis on the growth of two red tide microalgae Heterosigma akashiwo and Prorocentrum micans were studied in co-culture under the controlled laboratory conditions.The results showed that G.lemaneiformis inhibited the microalgal growth,or even caused mortality at end of the experiment.And the inhibitory effects were positively related to the initial densities of the seaweed.The cell number of microalgae was decreased markedly by increasing the initial densi...