The Effects of Lagrangian vs. Population Dynamics on Plankton Patchiness Generation

The relative importance of Lagrangian and population dynamics on spatial pattern formation in the distribution of plankton near the ocean's surface is investigated. Phytoplankton and zooplankton are treated as biologically interacting tracers that are passively advected by a divergence-free two-dimensional nonsteady velocity field. The time-dependence of this field is assumed to be quasiperiodic, which extends the analysis presented beyond standard chaotic advection. Various forms of predator--prey interactions, including complex interactions, are considered. Numerical simulations illustrate how Lagrangian dynamics, which is characterized by a mixed phase space with coexisting regular and chaotic motion regions, influences plankton patchiness generation depending on the nature of the biological interactions.