The Interspecific Competitions Between Microcystis Aeruginosa And Chlorella Pyreniodosa And The Factors Affecting On This Competition

Algal blooms significantly affect aquatic ecosystems with disrupting water body landscapes, decreasing water quality, and damaging aquaculture. It is acknowledged that explosion proceeding of the algae populations was affected by the environmental conditions and the interspecific competitions, yet little information is available on the mechanism of the dominance of harmful algae within algae assemblages in the eutrophication water body. In the present study, serial trials were conducted to explore the interspecific competitions between the harmful algae Microcystis aeruginosa and the cultural algae Chlorella pyrenoidosa under the extraneous nutrient load conditions and the predation impacts of Daphnia. The aim of this study is to explore the ecological mechanism of the formation of competitive advantage of M. aeruginosa to C. pyrenoidosa. The results showed that:1) The extraneous nutrients load such as the dry leaves had strong inhibitions on the population of M. aeruginosa and C. pyrenoidosa. Fish drug had significant toxicant effects on Chlorella sp., but promoted the growth of M. aeruginosa.2) The result of competition between M. aeruginosa and C. pyrenoidosa. was strongly related to their initial population density ratio, and such relation exhibit more evident on the impacts of Daphnia predation.3) Microcystis aeruginosa had strong toxic effect on the Daphnia. They declined the life span and the reproduction output of Daphnia, and by this way, they reinforced their competitive advantage on the impact of grazers predation.4) The fish predator, juvenile of Tanichthys albonubes, had strong effects on the Daphnia population. They promote the size and fecundity of Daphnia. On the other hand, these juvenile fish led to the dominance of large Daphnia. It promoted the impact of Daphnia on algae as the lager Daphnia has greater filter efficiency.5) The Daphnia could not utilize the M. aeruginosa, and as a result, they were suffered from starvation. However, they maintained their population in a short period by utilized the organic detritus that derived from the leaves degradation.6) In the experimental systems of extraneous nutrients load, algae, Daphnia and fish, M. aeruginosa did not showed clear competitive advantages to C. pyrenoidosa in eutrophication water. Additionally, this result was not change on the impact of grazer. Clearly, this might be result from the depression of leaves on the growth of M. aeruginosa. In general, I discovered that M. aeruginosa get the competitive advantage in the eutrophication water by escaping from the predation of grazer and by their greater ability on resource competitions.