Effect of Fishing on the Complex Dynamics of Marine Ecosystems

Marine ecosystems are complex nonlinear systems, and there biological varibles have low-dimensional nonlinear chaos characteristics. Under certain conditions, marine planktonic ecosystem can have different nonlinear dynamic properties, such as point attractor, periodic attractor as well as chaotic attractor. In this paper, a phytoplankton-fish (herbivorous) model was constructed. With the fishing intensity changed, we studied the nonlinear dynamic properties such as the stability and bifurcation of this model. Futhermore, a model consisting of 6 phytoplankton species and 4 zooplankton species extended with fishing factor was used to analyze the different attractors of the system under different fishing intensity. Results showed that fishing can promote the occurrence of alternative attractors. Futhermore, fishing will decrease the relative frequency of chaos. Under median fishing intensity, there will be more cyclic attractors which mean that population abundance varies mostly.