Morphological Characteristics Of Colony For Phaeocystis Globosa And The Influences Of Light And Calcium Ion On Formation And Cell Distribution Of Colony

Phaeocystis globosa has been studied for over one hundred years, which is commonly toform colony-dominated bloom in high latitude coastal regions. It has a complex life cycle thatalternates between solitary cells and colonies. Solitary cell is a few microns and, colony isgenerally several millimeters in diameter. Since1997, P. globosa bloom has quickly spread toChinese waters and become one of the most important HABs species. Unlike the strains in highlatitude, P. globosa in Chinese coasts has the characteristics of giantism colony formation andhemolysins generation. The giant colony may result in the unique structure and cell distribution.Both light and calcium are vital factors in growth and colony formation for P. globosa. However,the questions how they influence the colony formation and physiology of P. globosa are stillunclear.In the present study, the colony diameter, colony cell abundance and solitary cell abundancewere measured to investigate the correlations between contribution of solitary cell and colonycell to total biomass, colonial cell density and colony diameter of P. globosa Chinese strain. Theslope of linear regression relationship between colony cell number and colony diameter was usedto assess colonial cell distribution. Two P. globosa strains (non-colony form strain andcolony-form strain) were used to study the influences of light and Ca2+on the growth and colonyformation of P. globosa.Our results showed that colony was the dominant form during the polymorphic life cycle ofP. globosa. Log colonial cell abundance increased with log colonial diameter with the slope ofregression line of1.34, and the value was significantly less than previous results of other strains.The result shows that the colony of P. globosa Chinese strain contains relatively fewer cells perunit surface area. Both calcium and irradiance had significantly influence on growth, colonyformation and colonial cell distribution for P. globosa. The growth and colony formation of P.globosa was completely inhibited in calcium-free medium. The enlargement of colony andcolony abundance were hampered by low calcium; while compared with non-colony form strain,colony form strain was favor of high calcium conditions. The exposure of P. globosa to highlight (150μmol photons m2s-1) leaded to decline of biomass and colony abundance and raised colonial cell per unit colony surface area; Fv/Fmobviously decreased when non-colony formstrain grown at high light conditions, but there was no obviously difference in Fv/Fmbetweenhigh and low light (60μmol photons m2s-1) for colony-form strain.