The Life Cycle Of Phaeocystis Globosa And The Effects Of Light, Nutrient And Co-existing Diatom, Dinoflagellates

There had been an apparent increase in the occurrence of Phaeocystis globosa inChina Sea in recent years. Massive blooms of giant P. globosa along the Chinesecoast had caused serious environmental problems and economic losses. P. globosa hasa complex polymorphic life cycle that involves both colonial and solitary forms.P. globosa was grown in semi-continuous culture with three diatom species(Skeletonema costatum, Thalassiosira weissflogii and Chaetoceros curvisetus) or twodinoflagellates (Prorocentrum minimum and Alexandrium catenella) separately inorder to assess the effects of irradiance, nutrient limitation and their influence on P.globosa colony formation. The effects of allelochemicals on the colony formationwere assessed by adding the filtrate of diatom to the P. globosa culturing system. Theresults we could have were as follows:1. In the co-culture experiment of P. globosa and each diatom, the result showedthe adequate lightness could promote the growth of four species of algae otherwisewould restrained the growth significantly. P. globosa failed to form colonies underlight-limited conditions. The growth inhibition of P. globosa solitary cells and threediatoms was more significant under P-limited condition. The density of solitary cellswas higher in N-limitation conditions than that in P-limitation conditions. The colonyformation was significantly inhibited, as well nitrate was the favored nitrogen sourcefor the colony formation. Skeletonema costatum and P. globosa solitary cellspossessed higher competition than Thalassiosira weissflogii and Chaetoceroscurvisetus due to their smaller cell volume.2. The effect of P. globosa colony formation was assessed by adding the diatomfiltrate to the P. globosa culturing system. In non-nutrient limited conditions, thedensity of P. globosa colony was increased significantly while the diameter wassmaller. The furtherance was not significant for the P. globosa colony formation whenwe added the filtrate of each diatom to the P. globosa culturing system. In N-limitingconditions, the P. globosa colony formation was not significant.3. The cells of dinoflagellates possessed higher competition than P. globosa inthe co-culture experiment of dinoflagellates and P. globosa. The rapid consumption of nitrogen and phosphorus by dinoflagellates leaded to the lack of nitrogen andphosphorus in the system and oligotrophic environment in the medium-term training.As well the growth of p. globosa was constrained.