Studies Of Competing Between Three Marine Economical Microalgae And Heterosigma Carterae

At present red tide is a problem to be solved urgently. Actually red tide is the result of competing among species. Competing for resources and interacting occur between competitors, that is to prevent other competitors growing and keep themselves existing. Based on reading of many internal and international references, progresses on studies of competition among microalgae is summarilized to search the method to control red tide ecologycally in this paper. Through competing experiments between several economical microalgae and Heterosigma carterae, economical microalge is choiced which can evidently restrain harmful microalgae from growing. Then competitive mechanism is discussed through experiments about the relationship between cell concentrations and competition, competing for nutrition and allelopathy between microalgae. The main experimental results are following:1) Marine economical microalgae Nannnochloris oculata, Chlorella vulgaris, Phaeodactylum tricornutum and harmful microalgae Heterosigma carterae are experimental materials. Through competing experiments between three economical microalgae and Heterosigma carterae, the results show that three economical microalges can inhibit Heterosigma carterae from growing with different extent. The inhibitory effects of economical microalgae from weakness to evidence is below: Nannnochloris oculata < Chlorella vulgaris < Phaeodactylum tricornutu, and the effect is more evident as the initial density is higher. Under the initial density ratio is 2:1 of Chlorella vulgaris and Heterosigma carterae, Heterosigma carterae almost die the seventeenth day. The initial density ratio 2:1 is circumscription to inhibit Heterosigma carterae from growing. Under the initial density ratio is 1:1 of Phaeodactylum tricornutu and Heterosigma carterae, Heterosigma carterae will die after 7-9 day. Using linear regression method, the growth rates of Chlorella vulgaris, Phaeodactylum tricornutu and Heterosigma carterae are obtained, that is 0.5195, 0.425, 0.2652 respectively. The carrying capacity K is 632×104, 396×104, 62×104 cell/ml respectively. Utilizing Lotka-Volterra competition equations, competitive coefficients are calculated and this can allow a quantification of the strength of competition between economical microalgae and Heterosigma carterae. The results show that Phaeodactylum tricornutu is the best microalga to inhibit Heterosigma carterae from growing.2) Through competing experiments between Phaeodactylum tricornutum and Heterosigma carterae at different densities, the results show that Phaeodactylum tricornutum can inhibit Heterosigma carterae from growing with different extent when Heterosigma carterae is at different densities. And inhibitory effects is more evident as the initial density of Phaeodactylum tricornutum is higher. This makes out that inhibitory effects of Phaeodactylum tricornutum on Heterosigma carterae is connected with biomass. At the density of 10×104 cell/ml, Heterosigma carterae increases more quickly, is more deleterious to other organism and it is difficult to control. Maybe it is because Heterosigma carterae is at exponential phase.3) Through studies of competing for nutrition (nitrate and phosphate) between Phaeodactylum tricornutum and Heterosigma carterae, the results show that Phaeodactylum tricornutum can not endure the condition of low nitrate and phosphate well and can not exist, while Heterosigma carterae can endure the condition of low nitrate and phosphate well and can maintain biomass when no nitrate and phosphate are supplied. This makes out that Heterosigma carterae has better ability of competing for nutrition than Phaeodactylum tricornutum when nitrate and phosphate are limited. Heterosigma carterae dominates in competing when nitrate is enough and Phaeodactylum tricornutum will dominates when phosphate is enough. This makes out that Phaeodactylum tricornutum has better ability of competing for nutrition than Heterosigma carterae when nitrate and phosphate are high.The effect of phosphate on competing is more evident than nitrate. If environmental conditions benefits growing of Phaeodactylum tricornutum, correspondingly, Heterosigma carterae will grow badly. So it is feasible to control the trend of competing through adjusting of nutrient. 4) Effects of components (cultured fitrate, suspended cell, fragmented cellular fitrate and cellular fragments) of Phaeodactylum tricornutum on the growth of Heterosigma carterae are studied and competitive mechanism is discussed. The results show that components of Phaeodactylum tricornutum can inhibit Heterosigma carterae from growing respectively, and the inhibiting effect is more evident as the component is added more. It is possible that the inhibiting action of Phaeodactylum tricornutum to growth of Heterosigma carterae is connected with allelochemicals excreted by Phaeodactylum tricornutum.