Modelling and Simulation of the Mesoscale Mosaic Structure of the Lower Marine Trophic Levels

Marine ecology deals with biological and chemical processes in interaction with their aquatic environment. The possibility of using more of the products of the sea as human food has created at present a keen interest in the study of marine plankton. It is of importance to understand the production of pbytoplankton and the predator-prey relationships between phytoand zooplankton, the path by which the organic matter produced finally reaches the fish. In the sea, plankton populations are almost entirely at the mercy of water movement. In spite of this diffusive process, these populations display a spatio-temporal structure. The spectral analysis of the spatial organization of phytoplankton populations exhibits two main classes of behaviour depending on the range of spatial scale. Below 5 km, the phytoplankton behaves as a passive scalar i) from zero to IO0 m, the spatial variability of phytoplankton is eontr~lled by turbulence and its spectrum is similar to the spectrum of homogeneous and spatially isotropic turbulence according to Kolmogorov's theory, ii) from I00 m to 5 km, the coherence between chlorophyll and temperature are high. Beyond 5 km and until I00 km, the phytoplankton dynamics in promoting patchiness, i.e. mesoscale spatial heterogeneity, dominates over that of the physical diffusive processes in eroding it.