  We study a predator-prey model of plankton dynamics in the two and
three-dimensional wakes of turbulent flows behind a cylinder, focusing on the
impact of the three-dimensional character of the carrying velocity field on
population variance spectra and spatial distributions. By means of direct
numerical simulations, we find that the qualitative behavior of the biological
dynamics is mostly independent of the space dimensionality, which suggests that
only the relation between the typical flow and biological timescales is crucial
to observe persistent blooms. Similarly, in both cases, we find that the
spectral properties of the planktonic populations are essentially
indistinguishable from those of an inert tracer. The main difference arising
from the comparison of the two and three-dimensional configurations concerns
the local spatial distribution of plankton density fields. Indeed, the
three-dimensional turbulent dynamics tend to destroy the localized coherent
structures characterizing the two-dimensional flow, in which the planktonic
species are mostly concentrated, thus reducing the phytoplankton biomass in the
system.
