Effects Of UV-B Radiation Enhancement And Interspecies Interaction On Population Dynamics Of Skeletonema Costatum

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 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. Zooplankton grazing played an important role in the development of red tides, marine zooplankton selective grazing can significantly affect the phytoplankton community dynamics and control the rhythm, scale and fate of marine primary productivity. Enhanced UV-B (280nm-320nm) radiation resulting from ozone depletion is one of global environmental problems. Not only marine organisms But also marine ecosystem can be affected by enhanced UV-B radiation. UV-B radiation can significantly damage marine microalgae. The main targets are protein,DNA and photosynthetic pigments,and so on.A common red tide- Skeletonema costatum was selected to serve as experimental materials, and its growth were estimated under controlled laboratory conditions when stressed by P. helgolandicavar and enhanced UV-B radiation. The results could supply experimental base to answer the effect of enhanced UV-B radiation and interspecies on red tides, hence enhance our ability to understand and mitigate red t ides. Results showed:1 Effects of initial cell densities of S.costatum on population growth of S.costatumThe solitary culture methods were used to examine the effects of initial cell densities of S.costatum on population growth of S.costatum. The results showed that: The different initial cell densities of S.costatum have the apparent effects on its population growth. With promotion of the initial cell density,the time of entering exponential phase and stationary phase could be shortened,and the maximum population density could be decreased under solitary cultivated conditions;2 Effects of initial cell densities of S.costatum and different species of microalgae on population growth of S.costatumThe co-culture methods were used to examine the effects of P. helgolandicavar on population growth of S.costatum. The results showed that: The different effects were presented on population growth of S.costatum when stressed by P. helgolandicavar. The different initial cell densities of P. helgolandicavar also affected population growth of S.costatum, the inhibitation effect on S.costatum was increased gradually with increasing of initial cell densities of P. helgolandicavar in co-cultured system; the inhibitation effects were showed with curtate exponential phase and stationary phase, and decreased the maximum population density of S.costatum.3 Effect of enhanced UV-B radiation on population growth of S.costatum under solitary cultivated and co-cultivated conditionsThe ecotoxicological method was used to determine the effect of enhanced UV-B radiation on population growth of S.costatum under solitary cultivated. The results were showed as follows: UV-B radiation could stimulate the growth of S.costatum when the dose was lower than 1.2J/m2 while UV-B radiation also exhibited inhibitation effect to the growth of S.costatum when the dose was higher than 1.8J/m2, and inhibitation effect was enhanced with the increasing of UV-B radiation dose; The effect of enhanced UV-B radiation on S.costatum was changed under different initial cell density of S.costatum under solitary cultivated conditions, the inhibitation effect of enhanced UV-B radiation on S.costatum was presented an increasing first and then decreasing gradually with increasing of initial cell densities of S.costatum;4 Effect of enhanced UV-B radiation on population growth of S.costatum under solitary cultivated and co-cultivated conditionsThe ecotoxicological method was used to determine the effect of enhanced UV-B radiation on population growth of S.costatum under co-cultivated conditions with P. helgolandicavar. The results were showed that Population growth of S.costatum was changed by enhanced UV-B radiation under co-cultivated condition with P. helgolandicavar, the population cell density of S.costatum was decreased significantly in cultured system of P.helgolandicavar, and the inhibitation effect of enhanced UV-B radiation on S.costatum was increased gradually with increasing of initial cell densities of P.helgolandicavar in co-cultural system.5 Competition mechanisms between P. helgolandicavar and S.costatum and response to UV-B radiationThe ecotoxicological and statistics method was selected to examine interaction mechanisms between P. helgolandicavar and S.costatum and response of the interaction mechanics to UV-B radiation. Results indicated that interference competition and exploitation competition were coexistent in co-cultural system. P. helgolandicavar exhibited inhibitive effect to S.costatum through interference competition, S.costatum while presented an exploitation competition to P. helgolandicavar. The interaction mechanisms between P. helgolandicavar and S.costatum were changed by UV-B radiation stressed. A complete exploitation competition was showed between P. helgolandicavar and S.costatum after treated by UV-B radiation.