The influence of trophic interactions in the plankton community on its spatiotemporal dynamics

The present work considers a model of spatiotemporal dynamics for plankton community in a vertical column of water. Usually mesozooplankton (e.g. copepods) is considered as the main grazer in models of plankton systems. However, numerous studies have appeared recently that microzooplankton, not copepods, are the primary grazers in oceanic ecosystems. This work presents the model with microzooplankton and copepods as phytoplankton predators. Functional response for copepod feeding includes its preference for phytoplankton and microzooplankton. The effects of half saturation constants of zooplankton and diet variants on the stability of spatial homogeneous equilibriums was studied. In the case of effective grazing by mesozooplankton the system demonstrates stable coexistence of both zooplankton groups if phytoplankton carrying capacity is sufficient for it. In the case if microzooplankton protists are ineffective grazers – they are displaced by copepods or survive in a small number if their portion in the copepods diet is insignificant. The phenomenon of multistability has been identified in the system for copepod diet with microzooplankton preference. It means that several equilibria are stable at the same time, and the dynamics of the system are determined by the initial conditions. Allowing for spatial dependence in the modeled plankton community causes spatial structures appearance induced by Turing instability. It means that the system with diffusion only is able to induce stationary vertical profiles of plankton biomass. Such system state is possible if both predators are effective grazers and the microzooplankton prevails in the copepods diet.