Preliminary Study On Experimental Ecology Of Seaweed Gracilaria Lemaneiformis

The growth of Gracilaria lemaneiformis under different conditions, such as temperature,salinity, photon irradiances and inorganic nitrogen (DIN) and phosphorus (DIP) concentrations,N: P ratio and different chemical forms of nitrogen, were studied in the laboratory conditions.The inhibitory effects of G. lemaneiformis on phytoplankton community and two red tidemicroalgae, Heterosigma akashiwo and Prorocentrum micans, were studied in a co-culturingsystem with a series of indoor experiments.The results showed that the favorable temperature and salinity of G. lemaneiformis were25℃and 30‰, respectively. The weak illumination (20001x to 30001x) favors the growth of theseaweed. The chemical factors (N: P ratio from 10 to 15, higher concentration of NH₄⁺-N, theaddition of DIN(100 to 200μmol/L) could stimulate the growth of G. lemaneiformis.G. lemaneiformis had inhibitory effects on the phytoplankton and the growth of red tidemicroalgae, and the effect was positively related to the initial biomass of G. lemameiformis;increase in the initial biomass of G. lemameiformis decrease the cell densities of microalgae.Maximum inhibition effect occurred at the end of the experiment, the concentration causinginhibition to H. akashiwo was 0.996 when the biomass of G. lemameiformis was 20g/L, but to P.micah, it was just 0.663 and desreasing in the low initial biomass of G. lemameiformis. The cellsnumber of phytoplankton in the controll waters (without seaweed) was higher than in theexperimental waters (with seaweed), and Skeletonema costatum, Chaetoceros curvatus disapeardin experimental waters after the experiments began 3 days. Nutrient competitions between G.lemameiformis and the two red tide microalgae were noticed. G. lemameiformis showed acompetition advantage over the microalgae, while the two microalgae had effects of nutrientcompetition on growth of G. lemaneiformi. P. micans showed the higher ability of competitionwith G. lemaneiformi, and H. akashiwo appeared the lower. In addition, the aqueous extract of G.lemaneiformis had some inhibitory effects on the growth of H. akashiwo, but the effectsdecreased after dealing it with high temperature.