Effects of vertical velocity oscillations (associated with high frequency internal gravity waves) upon the vertical distribution of horizontally averaged phytoplankton concentration are considered. It is suggested that such effects have been systematically misrepresented in previous modeling efforts. Correction terms are derived both for averaged quasi-Lagrangian (isopycnal) models and for averaged Eulerian models. In quasi-Lagrangian models, an apparent modification to growth rate coefficient is obtained. In Eulerian models, velocity fluctuations are shown to induce a net vertical transport which can be described by a “virtual velocity” and which is seen as a correction to eddy diffusivity parameterizations. Difficulties such as negative or singular diffusivities are circumvented. Convergence of virtual velocity can provide an effective mechanism for formation of a phytoplankton maximum near or below the mean compensation depth. It is hoped that inclusion of effects here derived may extend the realism and utility of averaged plankton models.