Ecophysiological Response Of Gracilaria Lemaneiformis On Nitrogen Concentration Changes And The Relationship Between The Seaweed And Phytoplankton

The high value of Gracilaria for human food, abalone feed and agar production has led the fast development of the seaweed cultivation in the coastal waters in China. Gracilaria has very high productivity and can absorb large quantities of N, P and CO₂, produces large amount of O₂ and plays an important role in decreasing eutrophication. Gracilaria has become important bioremediation material in eutrophic coastal waters.The results from N-uptaked experiments showed that G. lemaneiformis assimilated prior NH₄-N other than NO₃-N at the same concentration. High concentration of NH₄-N can increase its absorption rate in the seaweed. Under the same concentration, NH₄-N and NO3-N were absorbed by seaweed in the similar rate. The growth, biochemical compositions and photosynthesis rate of G lemaneiformis were positively correlated with N-concentration of H.18μmol/L-89.44μmol/L, but the protein content was relatively stable. The photosynthetic rate of the seaweed increased in the range of the light intensity from 1000 to 40001x.The indoor experiments demonstrated that cultivated G lemaneiformis grew well in the enclosed pond. The growth of phytoplankton was depressed by G lemaneiformis. G. lemaneiformis can control the growth of red tide microalgae to a great extent.