We explore a numerical model of ocean biogeochemical cycles and the marine ecosystem in which many tens of functional groups are permitted. Their functional characteristics are attributed in a random process and natural selection determines the community structure. In ensemble integrations, in realistic one- and three-dimensional ocean settings with multiple limiting nutrients, robust and plausible regimes of community structure emerge. We will illustrate the model and discuss the application of this framework as a means to address and interpret the distribution of Prochlorococcus ecotypes along environmental gradients in the Atlantic Ocean.