Gelatinous zooplankton (jellyfish) and macrozooplankton are currently not part of systematic monitoring throughout the Baltic Sea region. This is largely due to the specific requirements of quantitative recording, which differ fundamentally from the monitoring of other, smaller zooplankton groups. The project aims to close identified data and knowledge gaps regarding the occurrence of jellyfish. A concrete concept for pilot monitoring will be developed,. Existing publications and datasets on macrozooplankton and jellyfish occurrence in the western Baltic Sea will be evaluated to create the baseline knowledge for the evaluation of potential trends.