| In recent decades, harmful algal blooms (HABs) occur frequently in marine coastal waters worldwide. This has caused disastrous damages to economic and public health. Many studies have begun to concentrate on the control of undesired algal growth, and allelochemical compounds of aquatic macrophytes may be potential candidates for the control of HABs. The present study deals with inhibitory effects of extracts of Eichhornia crassipes on three harmful algae Prorocentrum donghaiense, Phaeocystis globosa and Scrippsiella trochoidea. Inhibitory effects of extracts of fresh tissue and dry powder of E. crassipes and extracts of fresh tissue after autoclaved for 20 minutes at121℃ on the growth of microalgae were studied in this essay. The results showed that the growth of all three microalgae species was strongly inhibited by fresh tissue and by dry powder of extracts of E. crassipes at exposure concentrations(0.5-100g/L). The growth inhibition increased with the concentration of the extracts. It was found that LC50 of fresh tissue of E. crassipes to P. donghaiense, P. globosa and S. trochoidea were 0.93g/L, 4.90g/L and 9.80g/L at 96h of the experiment respectively and LC100 of dry power of E. crassipes to P. donghaiense, P. globosa and S. trochoidea were 20g/L,30g/L and 100g/L at 48h of the experiment respectively. There was some difference in the growth inhibition of the extracts of fresh tissue and dry powder of E.crassipes to microalgae, but the difference was not beyond 15%. It suggested that dry powder of E. crassipes also contain allelochemicals. After the extracts of fresh tissue of E. crassipes were autoclaved for 20 minutes at 121℃, the inhibitory effects of the extracts to P.donghaiense(at 2g/L) and S. trochoidea(at 10g/L) were obviously reduced and that increased to P. globosa(at 4g/L). The study have confirmed the inhibitory effects of extracts of E.crassipes on three harmful algae. Different microalgae showed different responses to the effects of the allelochemicals.
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