This PhD investigates how marine heatwaves reshape plankton community dynamics in the Belgian part of the North Sea (BPNS), where plankton is essential in food webs and biogeochemical fluxes yet are increasingly exposed to anthropogenic stressors. We first detect and characterize BPNS heatwaves using the Hobday method (≥5 days above the seasonal 90th-percentile SST), applying satellite SST data and validating against underway (~3 m) temperatures from the RV Simon Stevin as well as buoy data. The detected heatwaves events are compared based on intensity, duration, cumulative intensity, and timing across geographic and biologically defined regions. In parallel, we quantify phytoplankton and zooplankton composition, bloom timing, and abundance from the Belgian LifeWatch time series (zooplankton since 2014; phytoplankton since 2017) using ZooScan and Flowcam across nine coastal and eight offshore stations. By coupling physical extremes with community responses, this work advances mechanistic understanding and improves forecasting of plankton phenology and dominance shifts under a future of more frequent and intense marine heatwaves.