This thesis project will combine the development and the application of an ecosystem model including the integration of mixotrophy processes. The mathematical developments will allow to take into account the different types of mixotrophic organisms in an already existing ecological model which currently describes the functional groups in a classical way (autotrophic vs. heterotrophic). The model developed will be applied to a 3D model of the North Sea and validated before being applied for future scenarios. Field samples will be collected in the studied area and genomic data of plankton diversity will be analysed to study the importance of mixotrophic organisms in the North Sea and also used for model validation.