| Ozone layer depletion was one of the greatest global environmental problems. Because the depletion and the destruction of the ozone layer were becoming more and more serious, the ultraviolet radiation which reached the earth, esp. UV-B radiation which was harmful to the DNA of organisms, was strengthened. UV-B radiation enhancement has altered the whole ecological system on the earth's surface and emerged as one of the most noticeable global changes. The potential danger from the influence and injury of UV radiation on marine organisms (esp. marine plankton) has been increasing. On the other side, red tide was a global marine ecological calamity too. In recent years, there has been an increase in frequency, affected area and extent of injury of red tide outbreaks in coastal waters of our country.. Due to the worsened cultural environment and increased nutrient enrichment, red tides occurred more frequently than before and brought incalculable negative effect on marine ecology, fishery resources and sea-water aquaculture. Characterized by globalization, high frequency and great harm, nutrient enrichment and harmful red tides in coastal waters had become one of the most important fields among worldwide-concerned, newly-emerging significant marine environmental problems, which were associated with global changes and in bad need of being studied and solved.In this paper the responses of the interspecies competition between each two of three marine red tide algae of Alexandrium tamarense, Skeletonema costatum and Heterosigma akashiwo to UV-B radiation enhancement were studied by co-culture method. The results showed that 1. The growth characteristics of Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatum under different initial cell densities were different. The growth curves of three species of microalgae could be predicted by Logistic growth model. Different initial cell densities (0.2×l04cell/mL,0.4×l04cell/mL and 0.8×l04cell/mL) had apparent effects on the population growth of three species of microalgae. With the promoting of initial cell density, the time of entering exponential phase of growth and period of stationary phase shortened, and maximum population density decreased.2. The growth responses of Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatum toUV-B radiation enhancement was different. The growth of Heterosigma akashiwo was inhibited by UV-B radiation treatment, while lower dose of UV-B radiation could stimulate the growth of Alexandrium tamarense and Skeletonema costatum. However, higher dose of UV-B radiation also exhibited inhibitation to the growth of Alexandrium tamarense and Skeletonema costatum. The 96h.EC50 values of UV-B radiation treatment to Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatum were 1.63J/m2, 2.34J/m2 and 2.58J/m2 respectively.3. The UV-B radiation treatment could change the competition between Skeletonema costatum, Alexandrium tamarense and Heterosigma akashiwo.lt could promote the competitive dominance of Alexandrium tamarense. Therefore, the competitive dominance of Alexandrium tamarense changed more remarkable under UV-B radiation treatment when A:H=1:1 and A:H=4:1. Meanwhile, it could increase the competitive dominance of Skeletonema costatum and decrease the competitive dominance of Heterosigma akashiwo. when the inoculation proportions of Heterosigma akashiwo and Skeletonema costatum were H:S=1:4 and H:S=1:1, Skeletonema costatum was in predominance in this competition; However, Heterosigma akashiwo was in predominance when inoculation proportion was H:S=4:l.In the same time, it could promote the competitive dominance of Skeletonema costatum. Therefore, the competitive dominance of Skeletonema costatum changed more remarkably when A:S=1:4, and Skeletonema costatum was in predominance when A:S=1:1 under UV-B radiation treatment.This paper was significant to clarify the influence of the enhancement of UV-B radiation on marine ecological system and mechanism of red tide occurrence. |
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