Inhibition Effect Of Allelochemicals From Large Seaweeds On Gymnodinium Breve

Red tide is one of the most important ocean environmental problems with the development of industry recently. Because the technologies of controlling red tide have some shortcomings such as that some physical methods are not economic, and some chemicals used as red tide inhibitors are not safe for the ocean ecosystem. Therefore, safe, effective and economic red tide control technologies are desired. In competitive surroundings, marine organisms depend on simple physical defense, besides chemical defense also is the main method to compete with other organisms. In fact, chemical defense is that marine organisms usually release some chemicals to win dominance for their living, and the chemicals are allelochemicals in nature in the field of allelopathy. In ocean ecosystem, some large seaweed are known to produce chemicals to inhibit the growth of microalgae. In order to develop a safe, effective and economic red tide technology, the inhibitory effect of large seaweeds on the growth of Gymnodinium breve, isolation of the chemicals which can inhibit the growth of G. breve strongly from large seaweed, and the mechanism of allelochemicals working on G. breve are investigated.The allelopathy effect of seven species of large seaweeds (Undaria pinnatifida, Entermorpha clathrata, Grateloupia filicina, Sargassum sp, Ulva pertusa, Porphyra haitanensis and Sargassum fusiforme) on G. breve was investigated firstly. The results indicated that both U. pertusa could inhibit the growth of G. breve. The EC50 value was 1.45 g/L. Therefore, U. pertusa was used as materials for further isolation of allelochemicals.Six parts were got from U. pertusa, and the growth of G. breve was inhibited strongly by ethyl acetate fraction of all six fractions, and EC50 value of ethyl acetate fraction was 2.5 mg/L. Then the main chemicals in ethyl acetate fraction were detected by GC-MS. The results shown that there were 10 chemicals and the main part was phthalic acid esters (PAEs). The growth of G. breve was inhibited strongly by 1,2-Benzenedicarboxylic acid, butyl 2-methylpropyl ester (DIBP) and 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl)ester (DBP), and their EC50 values were 1.1 and 3.9 mg/L, respectively.Finally, the joint action of DIBP and DBP on G. breve was also investigated in this study. The results indicated that additive effect was main way of the two allelochemicals on G. breve.The mechanism of allelochemicals on G. breve was also investigated in this study. The results indicated that DIBP and DBP could induce the increase of reactive oxygen species (ROS) in algal cells, excessive ROS inhibited the activities of SOD and CAT, caused lipid oxidation, and destroyed the algal cells and resulted in the death of algal cells. This may be one of mechanisms of allelochemicals inhibiting the growth of algae. However, more detailed mechanism should be further confirmation.