Study On The Nonlinear Dynamics Of Plankton Ecosystem And Prediction Of Harmful Algal Blooms

Plankton ecosystem is a key component of the marine ecosystem, and it plays an important role in reglulating the structure and function of the marine ecosystem. The dynamics of the plankton ecosystem is a key theme and also a key difficult problemt in resolving the HABs. The detailed research work is as follows:First, we get an E-S-N model acoording to the control mechanism of the food chain. Using the key parameter as control variable, we research the stability and bifurcation of the system. Then based on ecological eutrophication, interaction of the algal and the prey of the phytoplankton, a P-P-Z model is constructed. Using the methods of the modern nonlinear dynamics, we discussed the bifurcation behaviors and stability of the model equations.A stochastic predator-prey model with function III response in a random environment is investigated. Conditions for the stability and Hopf-bifurcation of the deterministic model are worked out and stochastic stability about the positive interior equilibrium is studied. Last the numerical simulations are carried out to substantiate the analytical findings.With the aid of Ecopath with Ecosim mass-balance model and perturbation by fishing, the existence of alternative attractors in marine ecosystems was explored. The ecosystem was investigated in the form of bottom-up, mixed and top-down control respectively. Furthermore, fishery species were changed from wasp-waist to top predators. Thus, the effect of the trophic level to the existence of the alternative attractors was showed. The results proved that there were indeed alternative attractors in the studied ecosystems, and alternative attractors might be easier to appear from the systems with top-down control. As the fishing trophic level changed, the occurrence frequency of the alternative attractors changed slightly, but the models with alternative attractors changed significantly.Using the DELPHI7.0 of MS, a HABs early warning system is constructed based Windows9x. This system consists of three sub-systems: information system, decision system and urgent response system. The concept and principals of the ecosystem management are illuminated. Based ecosystem management we present an integrated management and prevention method of the HABs disaster.