The Allelopathy On Microalgaes Caused By Marine Macroalgaes

The relationship among marine organisms is complicated.And allelopathy exists in different sea plants and the different individuals of the same specieses.And allelapothy is a emerging method to treat the red tide.It is according to the inhibition of macroalgaes on the growth og microalgaes.In this article,three kinds of macroalges (Ulva pertusa、Gratelou piafilicina、Undaria pinnatifida) are choosed to research the allelopathy on two kinds of microalgaes (Alexandrium tamarense、Platymonas helgolandica).The aim is exploring the mechanism of allelopathy. The indicators mainly include:the cell count, EC50,MDA content, Chlorophyll-a content and carbon and nitrogen stable isotope analysis.The results are as follows:All three of macroalgaes have sensible allelopathy on Alexandrium tamarense, and Ulva pertusa have the strongest inhibition on Alexandrium tamarense according to the EC50 And as the concentrations of macroalgaes increase the inhibition effect becomes more obvios. However,the inhibitory effect of Ulva pertusa on Platymonas helgolandica is much weaker compared to Alexandrium tamarense.As for MDA concent, it increases rappidly in first few days after adding the macroalgaes.And MDA concent will be higher as the inhibitory effect increasing.As for Chl a content, when the microalgaes inhibited by the macroalgaes,the Chl a content of them is significantly lower than that in control group. And it becomes lower with the increase of the additon of extract solution。As for carbon stable isotope composition, under the allelopothy of Ulva pertusa,the δ13C value of Alexandrium tamarense increases obviousliy。And the higher concentration of Ulva pertusa is, the higher δ13C value of Alexandrium tamarense is。As for nitrogen stable isotope composition, the trend of δ15N value in experimental groups is similar to that in control group.However the d15N values of experimental groups are lower than that in control group.To sum up, macroalgaes have a significant allelopathy on microalgaes.The same macroalgae has different effect on different kinds of microalgaes.During the allelopahy of macroalgaes,MDA concent of microalgaes increases rapidly in first few days.And the chla concent decreses when the microalgae is inhibited by macroalges. Macroalgaes also have influence on carbon and nitrogen stable isotope composition of microalgaes.