MUTUAL PREDATION CAUSES BIFURCATIONS IN PELAGIC ECOSYSTEMS - THE SIMULATION-MODEL PLITCH (PLANKTONIC SWITCH), EXPERIMENTAL TESTS, AND THEORY

Zooplankton production is greatly dependent on the governing stability regimes of the ecosystems determining the flow of biomass transfer. M utual predation causes bifurcations or phase transitions between two o r more stable equilibria in pelagic communities. Minute changes in the phytoplankton reproduction rates caused by, for example, pollution ma y induce system changes from one stability regime to another. This piv otal behaviour of a simplified ecosystem was simulated, applying novel defniitions of population interactions in age-structured population m odels. The simulation model was then used for the localization of the most sensitive parts of the ecosystem, which were taken as guidelines for the experimental investigation of ecosystems synthesized according to the model requirements. It was possible to determine the congruenc ies as well as a non-compliance between the simulation model and the e xperimental results. By changing it accordingly, the simulation model was improved and developed further into a conceptual model of the cata strophic behaviour of plankton communities under the impact of mutual predation, a very general phenomenon in planktonic ecosystems. (C) 199 5 International Council for the Exploration of the Sea.