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Knowledge of the complex life cycle of Phaeocystis is a key to understanding its role in marine ecosystems and global biogeochemistry. An existing life cycle model was modified and used to integrate understanding of the Phaeocystis life cycle. In model-driven research, models expose gaps in our understanding, empirical studies ensue, and feedback improves understanding. Following this scheme, three facets of the life cycle model were examined here. With four exceptions, the empirical studies described have been presented in other literature citations. The first facet involved testing for the existence of a process or producing its description. These studies included: demonstration of in vitro colony division in Phaeocystis pouchetii, description of in vitro change in colony shape for P. pouchetii associated with senescence, determining which P. pouchetii life stage is vulnerable to viral infection and lysis, and an experiment designed to determine whether the sediment could be a source of new Phaeocystis colonies to overlying waters; results suggested that more-detailed investigation of benthic particles as a physical substrate for colony formation is warranted. The second facet involved investigation of process rate quantification or process control parameters. Process rate quantification included measurements of colony division rate and growth rate using mesocosm-derived colonies. Process control experiments included testing diatom frustule enhancement of P. pouchetii colony formation from solitary cells, and investigation of mesozooplanktonic suppression and microzooplanktonic enhancement of Phaeocystis globosa colony formation by planktonic grazer infochemicals. The third facet pertained to the molecular identification of genetic differences between single cells and colonies of P. globosa. These studies were designed to provide insight to the question of control factors involved in the transition between single cell and colonial life stages. The life cycle model provided a ready place to incorporate new insights and understanding from empirical studies into an existing model, and can be used to improve simulation models of the direct and indirect effects of Phaeocystis on global biogeochemistry. [ABSTRACT FROM AUTHOR]