This PhD project focussed on the North Sea’s viral diversity and dynamics. WP1 and WP2 delved into viral diversity and spatiotemporal dynamics through metagenomics and metatranscriptomics. WP3 studied virus-host causal networks and WP4 investigated the biogeochemical impact of viruses using viral production assays. Despite covid-related delays, the results underscore the significance of coastal seas through a viral lens.