Heterotrophic bacterioplankton and archaea constitute the largest living biomass in the oceans. These organisms need to take up labile dissolved organic matter substrates for growth and metabolism and they are exposed to two major mortality agents: heterotrophic nanoflagellates and viruses. Ultimately determining the biomass and activity of heterotrophic prokaryotes, these two factors (availability of substrates and mortality losses) are also known as bottom-up and top-down, respectively. The balance between bottom-up and top-down controls also affects the role of temperature in their standing stocks and productivity. We are interested in assessing the interplay between the three modes of control in different marine regions, with a special focus on nearby areas characterised by some of the hottest temperatures of the world ocean.
