Abstract A non-linear model is proposed to explain the horizontal structuration of prey—predator populations in a turbulent sea. The model is represented by a system of partial differential equations taking into account advection, due to residual currents, and eddy diffusivity. The ecological interactions are assumed to be of the Lotka-Volterra type. Starting from an initial small patch of prey—predator populations, numerical simulations show two distinct phases: 1. (i) an “explosive” phase corresponding to a bloom of phytoplankton and, 2. (ii) after that, a decrease of the quantity of plankton at the centre of the patch leading to a ring structure. The ring propagates in increasing its radius with constant intensity and velocity. The prey behaves like an “activator” and the predator like an “inhibitor”. The ring is thus similar to an active wave. When two waves meet each other, the simulation shows their “annihilation”. All these new properties of the prey-predator equations are in agreement with experimental data. Finally, the physical mechanism for initiation of patchiness is discussed.
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