Growth inhibition of queous extracts of Ulva pertusa on three species of microalgae in red tide

Aqueous extracts of Ulva pertusa were tested for allelopathic activity against three species of red tide microalgae, Heterosigma akashiwo, Skeletonema costatum, and Alexandrium tamarense. Within the first four days of the experiment, the growth of all the three species of microalgae were strongly inhibited at exposure concentrations(025～ 20?g·L-1). Maximum inhibition effect occurred at the 2～3?d of the experiment. The growth inhibition increased with the concentration of the extracts. The growth of H. akashiwo, and S. costatum were completely inhibited and A. tamarense was strongly suppressed at 20?g·L-1 treatment. The growth of microalgae was stimulated at lower concentration treatments (025～10?g·L-1) during the second half period (5～8?d) of the experiment. The inhibitory effects of the extracts to H. akashiwo and S. costatum could not be observed and that to A. tamarense was obviously reduced after autoclaved for 20 minutes at 120℃. 