Modelling the interactive effects of viral presence and global warming on Baltic Sea ecosystem dynamics

Abstract. Marine viruses have been identified as key players in biogeochemical cycles and in the termination of phytoplankton blooms; however, most models of biogeochemical processes have yet to resolve viral dynamics. Here, we incorporate a viral component into a 1D ecosystem model for the Baltic Sea to explore the influence of viruses on ecosystem dynamics under current and future climatic conditions. Virus host interactions and zooplankton grazing were mechanistically described through size-based contact rates. The model demonstrated that the presence of viruses increased nutrient retention in the upper water column. This corresponded to a reduction in phytoplankton biomass, production of dead organic matter and transfer of biomass to higher trophic levels. Viral presence played a key role in deeper water layers, near the thermocline. While warming alone reversed these trends, the combination of warming and viral presence enhanced the effect of viruses. Our results illustrate that marine ecosystem models need to incorporate viral dynamics to better predict system responses to climate change.