Transformation of dissolved organic matter and its diverse effect on higher trophic level

A considerable amount of primary production by marine phytoplankton is released to seawater as dissolved organic matter (DOM) via exudation and leakage processes. The labile fraction of DOM can either directly serve as a source of energy and nutrients or is transformed to particulate matter by abiotic gel particle formation. Principally, both pathways induce diverse effects on higher trophic levels, as they: (i) affect the growth of bacteria and photo-autotrophic nanoplankton, which directly affects the microbial foodweb, and (ii) enhance the formation of aggregates, which provide pelagic microhabitats but also accelerate the export of organic matter to the benthos. Reliable biogeochemical flux estimates of these distinct pathways will crucially depend on our understanding of small-scale processes. Here, we show examples that address the microbial turnover of organic matter and how it is related to primary and secondary production in the North Atlantic and at sites in shelf regions. Recent findings on the sensitivity of microbial processes to changes in temperature and pH will be incorporated. Ecosystems in coastal and shelf regions are most sensitive to anthropogenic impacts, as they are susceptible not only to global changes but also to regional changes. We will therefore give an outlook on how to improve monitoring, experimental, and modelling strategies to better account for microbial foodweb dynamics when assessing climate change effects on ecosystems in coastal and shelf regions