Many ocean ecosystems ar ethought to be heading towards a domiance of gelatinous organisms. However, gelatinous zooplakton has been largely understudied and the absence of quantitative long-term data for the studied area impeded drawing conclusion on the potential increasing densities. This study gives a comprehensive overview of the spatio-temporal distribution patterns of gealtinous zooplankton in terms of diversity and density bewteen March 2011 and February 2012 in the Belgian part of the North Sea and the adjacent Westerschelde estuary, based on monthly and seasonal samples respectively.