It has increasingly become accepted in recent years that ecosystems can only be managed sensibly if they are perceived and protected in their entirety. To this end, 12 principles for an ecosystem approach and 5 points of operational guidance have been elaborated in the framework of the Convention on Biological Diversity. They have not been applied to a marine ecosystem as yet. The “Ecosystem Research Wadden Sea” of 1989-1999 provides an appropriate case study for the practicality of these principles, because its integrative approach largely corresponds to the ecosystem approach.