Studies Of Grazing By Pavocalanus Crassirostris On The Solitary Cells Of Phaeocystis Globosa

Phaeocystis globosa bloom mainly appears in the form of colonies.Recently,Phaeocystis frequently blooms in tropical,subtropical,and temperate coastal waters as result of eutrophication and global warming.Predators grazing play an important role in regulating algae bloom.However,P.globosa have a heterogeneous life cycle that allows it to avoid the most grazing from predators by transforming from solitary cells to colonies.Therefore,to understand the role of predator in regulating P.globosa bloom,feeding on the solitary cells of P.globosa must be disclose.Firstly,the relationship between the solitary cells density and the colonies formation of P.globosa was test in different culture conditions.The following studies were conducted once confirmed that a certain solitary cells density is necessary for the colonies formation.Pavocalanus crassirostris,the dominant species of zooplankton in coastal water was use as the predator during the following experiments.Laboratory experiments were conduct to measure the grazing of P.crassirostris on solitary cells of P.globosa under different temperatures and diet concentrations and compositions.In the end,to evaluate the sustainable control ability of predator on solitary cell,the nutritional value of solitary cells of P.globosa and its effects on the growth and reproduction of P.crassirostris were assess.The main results were as follows:?1?Under the conditions of different temperatures or different nutrients,the density of solitary cells in the water body was different at the time of P.globosa colonies observed but all higher than 10×10³ cell ml^-1.The time for colony formation decreased with the increase of initial cell density.No colonies were found when the density of solitary cells?2?The highest ingestion rate on solitary cells of P.globosa by P.crassirostris was found during adult stage.No significant differences was found in ingestion rate of copepod in different temperature treatments?p>0.05?.Also,The ingestion rate increased with the increase of food cell ml^-1.In addition,in the mixing ratio of diatom to solitary cells of P.globosa,P.crassirostris has no selective grazing on solitary cells of P.globosa?3?Survival and egg production of P.crassirostris decreased when it long feeding on the diploid solitary cells of P.globosa?p<0.05?;however,egg hatching success was not significantly affected by diploid diet?p>0.05?.In contrast,no adversely affects were found when copepod feeding on haploid solitary cells.The survival rate,egg production and hatching success of P.crassirostris was 20.07±2.18%,solitary cells.While the survival rate,egg production and hatching success of P.crassirostris was 41.75±4.69%,36.05±26.70 eggs ind^-1 and91.34±3.52%in the diet treatment of haploid solitary cells.The results of the fatty acid analysis revealed that haploid solitary cells of P.globosa were a nutrition-rich food for P.crassirostris.In contrast,the diploid solitary cells of P.globosa were not suitable food for P.crassirostris because of the deficiency of polyunsaturated fatty acids?PUFA??5.60%?and absence of DHA and EPA which is necessary for copepods growth and reproduction.