Population Growth And Interspecific Competition Of Marine Microalgae And Their Response To Enhanced Cd²⁺

Heavy metal pollution have found in many countries with the development.of economy More and more attention has been put into this problem while the heavy metal with extensive sources can transfer along the food chain, accumulte easily and be hard to recover. It is inevitably for marinr ecosystem to be polluted. As the main primary producers, marine microalgae plays an important role in material cycle and energy flow and is also the pathway of pollutants entering the food web. Flow Cytometry (FCM) is a rapid method for the quantitative measurement for individual cell in moving fluid. Measurements of multiple fluorescence properties of thousands of individual cells are collected simultaneously to detect physiological status of cells. Flow cytometry only recently been applied to ecotoxicological studies, but has aroused increasing interest among researchers. This study was aim at eluminating the possible effects of Cd²⁺ on the growth of different species of microalgae and on the interactions among them. Three species of marine microalgae : Platymonas helgolandica (Chlorophyta), Heterosigma akashiwo (Rhaphidophyta) and Prorocentrum minimum(Dinophyta) The toxic effects of Cd²⁺ on these microalgae are analyzed under controlled laboratory conditions, and results show that:1. the effect of enhanced Cd²⁺ concentrations on three kinds of microalgae in acute test(1) P. helgolandica, H. akashiwo and P. minimum can be easily distingusihed with bacteria, cell debris and suspended particles by use of FCM, which was the base of following the analysis.(2) many kinds of fluorescene light were analyzed and th e data on cell volume, cellular content complexity, chlorophyll a (Chl a) fluorescence, survival rate, and content of reactive oxygen species (ROS) was obtained. Both the content of Chl a and the survival rates decreased with the concentration of Cd²⁺ increasing. Howerever, the content of ROS increased obviously. The response of the cell volume and cellular content complexity was depend on the species. The cell volume and celluar content complexity largened for P. helgolandica when the concentration of Cd²⁺ increased. However, the cell volume of other two kinds diminished, and the cell content complexity turned different perormance whlie H. akashiwo's decreased and P. minimum's increased.(3) For three kinds of marine microalgae, the content of chlorophyll a, the survival rates and the level of ROS had the same tendancy on the base of flow cytometry, respectively. These three indexes could be as indicators to response to Cd²⁺ exposure.2. Effect of acute Cd²⁺ exposure on three kinds of microalgae in bi-algal culture(1) P. helgolandica, H. akashiwo and P. minimum can be easily distingusihed with bacteria, cell debris and suspended particles by use of FCM, which was the base of following the analysis. It was also easy to separate one marine microalgae to other in bi-algal culture.(2) It was obvious to observe that Cd²⁺ had toxic effect on two kinds of microalgae in co-culture. The population size of marine microalgae diminished according to the gates of R1 and R2 which seted by forward scatter and side scatter. The cellular content complexity increased while the level of chlorophyll a rose for microalgae in all co-culture system except P. helgolandica in co-culture with P. minimum. The cell volumn of H. akashiwo and P. minimum decreased in co-culture afer Cd²⁺ added to the medium. Morever, the stress made the cell volumn of P. helgolandica lessen and the cell volumn of P. minimum largen in bi-algal culture. The cell volumn of H. akashiwo had no change while the cell volumn of P. minimum declined in the co-culture.