ECOLOGICAL MODELING OF THE NORTH-SEA

North Sea ecosystem models published in accessible literature are partitioned into groups with respect to their emphasis on significance and detail of different trophic levels of the ecosystem. These subsets are treated separately in the three main chapters, which deal with relationships with physical dynamics, lower trophic level interactions and higher trophic level interactions. They are preceded by chapters that introduce the scope of the models, the history of modelling approaches, main purposes and specific aims, general aspects of internal structure, and modelling techniques applied. The main chapters compare the process descriptions characteristic of the subsets of models, and discuss aims and results with emphasis on significance and contribution of the processes considered. The chapter on plankton dynamics in relation to physical dynamics relates plankton responses in the mixed layer to changes in the physical environment. Attention is given to seasonal forcing functions, the coupling of horizontal and vertical plankton distributions, the flow of matter and the sensitivity of the plankton system. The chapter on lower trophic levels deals with primary production and its limiting factors, nutrient cycles, eutrophication, the microbial loop, and mineralization of organic matter in the pelagic and benthic compartments. The chapter on higher trophic levels highlights predator-prey interactions, the impact of grazing, and the significance of predation for system stability. A final chapter discusses what has been achieved so far with models of North Sea ecosystems and what must be aimed at in the future. It argues for lucidity and more methodology in simplification to the degree allowed by the questions to be solved, more attention for models as carriers of unifying concepts in marine ecological theory, technical solutions in handling different time and space scales for different processes and distributions, cooperation of different disciplines to find answers to questions of general importance, and the formation of data bases for model validation.