Effect of five chinese traditional medicines on the biological activity of a red-tide causing alga—Alexandrium tamarense

The activity of algal cells plays an important role in the development of a red tide. Thus, when mass sedimentation of algae occurs, the scale of the red tide is reduced to some degree. Using cell suspension ability as an indicator, we studied the inhibitory effect of five Chinese traditional medicines/Chinese herbs on the activity of the red tide causing alga, Alexandrium tamarense, strain DH01. The results showed that among the five herbs, golden thread (Rhizoma coptidis Huang Lian) and areca seed (Semen arecae Bing Lang) had the best inhibitory effect, followed by indigowoad (Isatis tinctoria L.), and the least effect was found in lightyellow sophora (Sophora flavescens Ait.) and chameleon plant (Houttuynia cordata Thunb.). The 1hLC₅₀ of golden thread and areca seed was 0.054% (w/v) and 0.074% (w/v), respectively. Moreover, the higher the concentration of the herbs, the higher the inhibitory rate (IR), and the shorter reaction time needed. Combination of two herbs improved, to some extent, the inhibitory effect on the algae. A mixture of golden thread and areca seed was the most effective treatment against cell mobility of this red tide alga, and the 1 h inhibitory rate was 70.7%. Next most effective was the combination of indigowoad root and lightyellow sophora. The best inhibition results in the experiments using absorbents were golden thread and indigowoad with aloe (Aloe vera L. var. chinensis (Haw.) Berg.); followed by areca seed with aloe, and golden thread and areca seed with kelp (Laminaria japonica). In general, the zeolite based algal inhibitors were less effective. The inhibitory rates of the algal inhibitors LA, LI, KG, KA and KG were all above 90%, and remained high for 72 h. Our research results showed that the red tide inhibitors made with Chinese herbs, such as golden thread and areca seed, had the merits of low concentration, fast reaction time, and demonstrated a promising future for use in the control of red tides.