Effects Of Anthracene On The Population Growth And Interspecific Competition Between Two Species Of Marine Microalgae Under Controlled Laboratory Conditions

Global marine oil pollution is one of the most serious problems of marine pollution that people focus attention upon and need to be solved urgently. Polycyclic aromatic hydrocarbons (PAHs) are assumed to be the most toxic component of oil to marine organisms. Since some PAHs are known carcinogens and mutagens, these ubiquitous environmental pollutants are on the United States Environmental Protection Agency's priority pollutant list. Anthracene (ANT), one typical individual compound of PAHs, has the simplest linear structure. It is one of sixteen individual PAH compounds which have been identified as priority pollutants. Researches on ANT's toxicity can provide basic experimental evidences for further studies about complex PAHs. Algae, the major primary producers in the marine ecosystem, play an important role in the fate of PAHs in aquatic ecosystems. Many studies indicate that ANT has significant effects on marine microalgae.Platymonas helgolandica var. tsingtaoensis and Heterosigma akashiwo are selected to serve as target organisms in this study. The main objective of this work is to determine the microalgal population growth dynamics at different initial cell density in mono-culture, and their growth changes and interspecific interactions with different initial biomass ratio in co-culture with and without ANT stress under controlled laboratory conditions. The purpose of the present study is to provide scientific basic to investigate effects of PAHs on aquatic ecosystems, and supply theoretical evidences to study the community succession of marine microalgae and marine environmental monitoring.Results showed as followed:A. Effects of different microalgal initial cell densities on population growth of P. helgolandica and H. akashiwo in mono-culture (1) The population growth of both P. helgolandica and H. akashiwo can be fitted with the logistic growth model. Different microalgal initial cell densities have pronounced different effects on the time of entering exponential phase and stationary phase, the intrinsic growth rates (r) and the carrying capability (K): the time of entering exponential phase and stationary phase are shorter with initial cell densities increasing;(2) The value of r is highest when the initial density is lowest. When the initial cell density is 0.125×10~4cells/mL, there is the highest value of r. The highest value of r of H. akashiwo is larger than P. helgolandica. The highest value of r of H. akashiwo is about 1 times higher than P. helgolandica.(3) There is no marked change in the value of K with the increased initial cell densities. There are pronounced differences in the highest K value between the two microalgal species. The highest value of K of P. helgolandica is about 3 times higher than that of H. akashiwo.B. Effects of different proportions of the microalgal initial biomass on the interactions between P. helgolandica and H. akashiwo in the bialgal culture(1) The population growth and interspecific interactions between P. helgolandica and H. akashiwo are investigated at different initial biomass ratios in the bi-algal culture. The population growth of both microalgal species can be fitted with the logistic growth model. The competition model of Lotka-Volterra can be used to analyze the interspecific competition between the two microalgae. The results show that, firstly, H. akashiwo (ab. H) can out-compete P. helgolandica (ab. P) in the competition when the initial proportion is set at P: H = 1: 4 and 1: 1. Secondly, the interaction between the two microalgal species might be coexistence at the proportion of P: H = 4: 1, but this equilibrium is unstable.(2) There are two types of competition between the two microalgal species, exploitative competition and interference competition.C. Effects of ANT on the interactions between P. helgolandica and H. akashiwo in the bi-algal culture(1) The ecotoxicological method is used to determine the effect of ANT on the interactions between P. helgolandica and H. akashiwo. The results show that there is different sensitivity of the two microalgal species exposed to ANT. The tolerance of P. helgolandica to ANT was greater than H. akashiwo. Compared to the monoculture when exposed to ANT stress, there is a significant effect of ANT on the population growth of P. helgolandica in the bi-algal culture.(2) When P. helgolandica and H. akashiwo are exposed to low concentration of ANT, their relative growth rates become higher. It is showed that low concentration of ANT can obviously stimulate the growth of the two microalgae, and their relative growth rates increase when the concentration of ANT is lower. On the contrary, high concentration of ANT has negative effect on the population growth of two microalgae, and the relative growth rates of the two microalgae decrease with the concentration of ANT increased.(3) In the bi-algal cultrue, effects of ANT on the interspecific competition between P. helgolandica and H. akashiwo are measured by using ecotoxicological method. The results show that the interspecific competition between the two microalgal species can be changed when exposed to ANT. H. akashiwo plays the dominant role in the competition at three different initial proportions without ANT stress. In contrast, the interspecific competition between two species of microalgae changes in the bi-algal culture with ANT stress and P. helgolandica becomes dominant species in such condition. The results of this work show that the competitive ability of H. akashiwo is weakened when exposed to ANT, whereas the competitive ability of P. helgolandica is significantly enhanced, and finally the interspecific competition between P. helgolandica and H. akashiwo changes in the bi-algal culture with ANT stress compared to the control group (without ANT stress).