Effects Of Diatom On The Growth And Colony Formation In Phaeocystis Globosa

Phaeocystis globosa is a common harmful bloom species in the coastal of China.Its' frequent outbreaks of blooms have caused serious economic losses and ecological hazards.P.globosa has a complex and polymorphic life cycle.It can alternate between free-form single cells and gelatinous colonies.The formation of colony is usually responsible for the occurrence and development of algal blooms.In the ocean.Phaeocystis blooms generally occur seasonally after the diatoms bloom.Therefore,it is of great significance to study the relationship between diatoms and colony formation of.globosa for revealing the mechanism involved in colony formation of Phaeocyslis and the control of Phaeocystis blooms.In this paper,the phytoplank-ton community diversity and community structure characteristics during the outbreak of P.globosa bloom in the Beibu Gulf of Guangxi province.China were studied.Meanwhile,the diatom Ditiylum brightwellii,Chaetoceros pseudocurvisetus were selected to investigate the effects of the diatom on the colony formation and growth of P.globosa in lab experiment.The main results are as follows:1.A total of 103 species belonging to 46 genera were identified from surface water samples collected from Beibu Bay when P.globosa bloom happened.Among them.diatoms contained with 42 genera(92 species)are the main phytoplankton groups in this area,accounting for 89.3%of the total species.The dominant species were P.globosa.Chaetoceros and Guinardia.Importantly,the areas with high abundance of diatom species and P.globosa overlapped,suggesting the correlation between diatoms and P.globosa bloom outbreak.2.Different species of diatoms have different effects on the colony formation of P.globosa.The promotion of a diatom on the colony formation is based on the existence of a certain difference of density between them.The initial density ratio of P.globosa to a diatom must be at least 10:1.3.When the initial density of P.globo.sa was low(102 cells/mL),C.pseudocurvisetus promoted the colony formation of P.globosa.When the initial density of P.globosa was medium(103 cells/mL),D.brightvtwellii promoted the colony formation of P.globosa.When the initial density of P.globosa was high(104 cells/mL).diatoms did not promote the colony formation.Because when the density of P.globosa is high.P.globosa can easily form colony.4.D.bnighellii and C.psvedocurvisetus had promoted the early formation of the colony,increased the size of the colony at the early growth stage,and also played a role in the maintenance of the colony in the later growth stage.5.When the initial density of P.globosa was 10-4 cells/mL.the filtrate of the culture medium during the decline period of D.brightwellii had inhibited the colony formation and decreased the diameter of the colony of P.globosa.When the initial density of P.globosa was 103 cells/mL,the filtrate of the culture medium during the logarithmic growth phase of D.brightwellii had promoted the colony formation of P.globosa and increased the colony diameter.