Growth Characteristics Of Two Diatoms In Culture Media And Aquacuktre Wasterwaters

In the past several decades, harmful algal blooms (HAB) increased in frequency, intensity and geographic distribution all over the world. Thus, HAB pose a grove and expanding threat to fishery resources, especially to public health of human. Recently, very little research on HAB has been done in China; therefore, to reveal the relationships between key environmental factors and HAB is of great importance to control HAB in saline aquaculture areas effectively.Two diatoms(Skeletonema costatum and Chaetoceros curvisetus), as tested harmful algae, were used to study the effect of nutrient input on Skeletonema costatum growth and the ecological factors on Chaetoceros curvisetus growth, as well as different initial cell density on population competition between two diatoms. The environmental factors influencing HAB were also studied by simulative culture experiments in Dafeng and Tsingtao, in terms of diffusion characteristics of aquaculture wastewater into the sea. The results are described as follows:The effect of the initial cell densities on the Skeletonema costatum growth was studied on the conditions of different phosphate concentrations and the f/2 substrate. The specific growth rate ranged from 0.125 to 0.252 and varied a little with different phosphate concentrations and initial cell densities, while it was slightly higher at low initial cell density; the biomass yield was lowest at the low level of initial cell density and phosphate concentration. The population density was 10% of that as compared to the high level of initial cell density and phosphate concentration.Comparative studies were carried out to determine the effects of environmental factors, i.e. temperature, light intensity, salinity and pH on the growth of Chaetoceros curvisetus. The best growth conditions are 20℃, 40001x illumination, salinity 25‰and 8.3 pH. This condition obtained the maximum specific growth rate and the highest cell density.The effect of initial cell density on the population competition between Skeletonema costatum and Chaetoceros curvisetus was studied in this experiment. The results demonstrated that, different initial cell densities (0.4×10⁴, 0.6×10⁴, 1.2×10⁴cell·mL^-1) had significant effects on the cell density of Skeletonema costatum and Chaetoceros curvisetus when cultured alone. The cell densities of Skeletonema costatum and Chaetoceros curvisetus increased with inaeasing initial cell density. In the mixed culture, the growth of the two species was inhibited, and the influence extent on Skeletonema costatum was greater than that on Chaetoceros curvisetus as compared to the pure culture conditions. Calculated by the inter-specific competitive parameters, Chaetoceros curvisetus had a stronger interspecific competitive capacity and about 11 times of that of Skeletonema costatum.A simulative culture experiment with seawater and aquaculture wastewater, which was derived from Dafeng and Tsingtao, was also conducted. The result showed that, the algae biomass increased in the seawater with low level nutrients, indicating eutrophication was one of factor causing red tide. It is demonstrated that the growth rate of algae was relatively lower under low nutrient concentration conditions. However, the growth rate and the biomass of algae increased to its maximum, and the stationary growth phase sustained longer time when adding aquaculture wastewater into seawater. In terms of above-mentioned description, we concluded that aquaculture effluent caused and accelerated HAB.