Abstract: The effects of cleaning dredged materials on the growth of two marine microalgae species with different initial cell density:Skeletonema costatum and Heterosigma akashiwo, were investigated by using the measures of experimental ecology. The results show that at the unialgal culture medium of cleaning dredged materials in laboratory, the different initial cell density has apparent effects on the growth of microalgae. At the initial cell density of 0.2×10⁴ cells·mL^-1, the time of entering exponential phase and stationary phase can be extended, and reaching the maximum cell density is higher; at the initial cell density of 0.8×10⁴ cells·mL^-1, the time of entering exponential phase and stationary phase could be shortened, and reaching the maximum cell density is reduced. For the mixed cleaning dredged materials culture medium, the different initial cell density has apparent effects on the relation of interspecific competition between two species of microalgae. There is obvious interspecific competition between S. costatum and H. akashiwo. H. akashiwo has predominance in this competition, and S. costatum suffers from H. Akashiwo inhibition, within the entire experimental period, cell density reduces very significantly and is lower than that in the unialgal culture, while H. akashiwo cell density is not significantly reduced. Among these three different medium concentrations of cleaning dredged materials, the cell density in the highest culture medium concentrations of 1 000 mg·L^-1 is significantly lower than those in 100 mg·L^-1 and 500 mg·L^-1 culture medium, and the cell density is the highest in 100 mg·L^-1 culture medium. This indicates that the greater of clean dredged materials concentrations, the greater effects on the growth of microalgae, while the lower of clean dredged materials concentrations, the smaller effects on the growth of microalgae.

Key words: cleaning dredged materials, interspecific competition, initial cell density, Skeletonema costatum, Heterosigma akashiwo