Numerical study of plankton–fish dynamics in a spatially structured and noisy environment

The effects of mobile fish schools and noisy zooplankton mortality on the plankton dynamics are described, using a minimal model of the nutrients–plankton–fish food chain. The space is divided into three habitats of different phytoplankton growth, a first with high productivity, connected to the second with productivity, linearly decreasing down to the level of the third habitat. The plankton growth, interactions and transport are modeled with reaction–diffusion equations whereas, the fish school motion is discrete and rule-based, depending on the local zooplankton density as well as on spatial position, previous direction and maximum residence time.