Studies On Allelopathic Effects Of Extracts From Mangrove Leaves On Algae

Red tide has become one of the world's recognized marine disasters, which not only results inserious environmental and economic problems, but also poses a serious threat to human healthand safety. Thus, it is imperative to seek some safe and effective ways to prevent and control thered tide outbreak. The presence of mangrove allelopathy provides a new approach for thebiological control of red tide. In this study, five typical mangrove plants Bruguiera gymnorrhiza,Kandelia candel, Excoecaria agallocha, Cerbera manghas, Acanthus ebracteatus and two redtide algae Phaeocystis globosa and Heterosigma akashiwo were chosen to investigate theinhibitory effects of aqueous extracts from mangrove plants powder and fresh tissue on the twored tide algae. What's more, the inhibitory effects of organic solvent extracts from B.gymnorrhiza on the growth of P. globosa, the effects of heat treatment on the algaecidal effectsof aqueous extracts from mangrove plants, and the effects of extracts at different initial algaldensity (IAD) on the growth of algae were elucidated. The results showed that, mangrovepowder and fresh tissue aqueous extracts could significantly inhibit the growth of Phaeocystisglobosa and Heterosigma akashiwo. The inhibitory effects of powder aqueous extracts on thetwo red tide algae were in the order of E. agallocha>K. candel>A. ebracteatus>B. gymnorrhiza>C. manghas. In our study, fresh tissue aqueous extracts of B. gymnorrhiza and K. candel hadstronger algaecidal effects. Heat treatment study showed that algaecidal allelochemicals ofaqueous extracts from K. candel and E. agallocha were relatively unstable, but those from B.gymnorrhiza and A. ebracteatus were relatively stable under high temperature condition. Fromalgaecidal experiments with organic solvent extracts of B. gymnorrhiza, we found that four kindsof the extracts had significantly inhibitive effects on P. globosa, and the inhibitive effects ofextracts of hexane phase and ethyl acetate phase were stronger than those of n-butyl alcoholphase and water phase. The48h-EC50of extracts of hexane phase and ethyl acetate phase on P. globosa was14.90and12.18mg/L, respectively. The initial algal density (IAD) was consideredas an important factor influencing the inhibitive effects of extracts. The inhibitive rate (IR) washigh at low IAD, and the IR decreased with the increasing of IAD. At a higher IAD, the extractspromoted, but did not inhibit the growth of P. globosa.