Bacteria-zooplankton interactions: a key to understanding bacterial dynamics and biogeochemical processes in lakes?

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Worldwide, metazoan zooplankton represents an enormous surface and biomass in pelagic systems but their linkage with bacteria has been assumed to be rather indirect (via nutrient cycling and trophic cascades). However, a zooplankter’s body carries a high abundance of diverse bacteria, which can account for a substantial fraction and diversity of pelagic bacteria. Zooplankton bodies are organic-rich micro-environments that support fast bacterial growth. Their physical-chemical conditions differ from those in the surrounding water and hence select for different bacterial communities. Until now, information on bacteria- zooplankton interactions is still limited to only a few zooplankton groups and environments, in particular copepods in coastal and estuarine waters. Therefore, our proposal focuses on bacteria-zooplankton interactions in lakes. Since zooplankton taxa can have very different life history traits we will compare a large number of zooplankton taxa in a variety of lakes. In field and lab studies we will investigate these interactions with a high spatial and temporal resolution. We will address 4 topics: A) spatial and temporal variations in bacteria-zooplankton association, B) microbial dynamics in the zooplankton gut microhabitat, C) bacterial dispersal by migrating zooplankton and D) effects on microbial activities during the mid-summer zooplankton decline. We aim to fundamentally change the way we understand pelagic food webs and the ecological role of bacteria-metazoan interactions.