Huge complex ecosystem models with several hundred parameters andlarge input data sets escape standard attempts at integral assessment.We introduce the concept of group-collecting sensitivity analysisin which related model parameters or forcing coefficients are combinedinto subsets. Since means and standard deviations of subsets are variedinstead of individual coefficients, the method is numerically efficient andproduces a condensed amount of results. Application to the AquaticEcosystem Model (AQEM) is presented. AQEM is a descendantof the European Regional Seas Ecosystem Model (ERSEM) with a finerprocess and spatial resolution with respect to the Wadden Sea. Atwo-dimensional sub-structured sensitivity table, which is the major resultof this approach, enables an immediate perception of sensitive functionalrelationships and dependencies between individual parameters and therelevant characteristics of a near-shore aquatic ecosystem. Specialemphasis is placed on differences in average and seasonal behaviour.The response of selected result variables to the variations of the majorityof group parameters is correlated, i.e. result variables show a similarsensitivity to variations in a specific parameter group. We show thatexceptions to this rule lead to a deeper insight into the model system.