Connecting models, networks and experiments: Revisiting the role of viruses in marine carbon cycling
The marine microbial food web is a key driver of global carbon cycling, mediating the production, consumption and remineralisation of organic matter in the ocean. Within this food web, viruses exert strong top-down control by infecting and lysing both phytoplankton and heterotrophic bacteria. Although virus-induced mortality is recognised as a factor shaping microbial dynamics, accurately quantifying its contribution to carbon cycling remains difficult. A range of approaches have been used to estimate this contribution, notably: (1) dynamical microbial ecosystem models, (2) static carbon flux networks, and (3) direct measurements of virus-induced mortality, such as dilution assays. In this study, we bring these approaches together by formulating them within a common mathematical framework. This enables us to clarify the difference between two notions of lysis percentage in the literature, to compare predictions of previous microbial ecosystem models and flux network reconstructions, and to critically evaluate the theoretical approach of eliminating viruses from the system to explore their effects. Our analysis clarifies how the different approaches capture complementary aspects of the role of marine viruses in carbon cycling across varying spatial and temporal scales.