Marine mesozooplankton play a crucial role in the functioning of pelagic ecosystems and global biogeochemical cycles. It is very diverse from a taxonomic and phylogenetic point of view (e.g., giant protists, copepod, krill, small jellyfish, fish larvae), but also functionally (e.g., small vs. large organisms, herbivores who are filtering-courant feeders vs. carnivores who are ambush feeders, vertical migrations, lipid reserve production, etc.). Yet, the link between mesozooplankton diversity and ecosystem functioning remains poorly understood.? TRAITZOO aims to decipher this link using a trait-based approach and taking advantage of recent developments in high-throughput sequencing and imaging of marine plankton. Using already available data, that has been collected in various biogeographical provinces of the global ocean and covering wide environmental gradients, mostly collected by our consortium, we will use numerical ecology and machine learning tools to 1) provide new tools to study functional traits from imaging and transcriptomic data, 2) describe the biogeography of functional traits and identify the main drivers of mesozooplankton functional diversity, and 3) improve marine ecosystem models and develop new trait-based models to better quantify plankton-mediated carbon fluxes. Our consortium brings together experts in mesozooplankton ecology and physiology, marine biogeochemistry, and applied mathematics. Our skills cover plankton imaging, transcriptomics, metabarcoding, biogeochemical modelling, individual-based modelling, statistics, and machine learning.