Summary

Mid trophic levels (MTL) are essential for channelling resources across marine food webs influencing the transfer of primary production to upper trophic levels. Recent discoveries suggest that MTL (e.g. zooplankton and planktivorous fish) may enhance this transfer by combining inputs from microbial and metazoan food webs, thus increasing overall trophic efficiency and food chain length.These findings challenge the current paradigm of low trophic efficiency and short food chains leading to large stocks of high trophic level species (e.g. carnivorous fish). The aim of this project is to advance our understanding of the role of MTL in the functioning of marine food webs through the exploitation of microbial and metazoan resources. Specifically, the project will address the identification of MTL species with large microbial contribution, the influence of structural and functional diversity of microbial and metazoan communities on microbial contribution, and the main drivers of trophic efficiency at seasonal and spatial (habitat) scales. Given the importance of MTL for sustaining healthy and productive food webs and the expected increase of microbial food webs in the near future, the knowledge compiled by this project will be useful to i) understand the taxonomic and ecological constraints to microbial contribution; ii) better quantify the trophic efficiency of marine food webs, and iii) facilitate the prediction of changes in marine food webs as a consequence of global change.