1 Introduction Oceanic protists (OP) comprise an exceptionally diverse group of microbial eukaryotes that underpin marine ecosystem functioning through primary production, grazing, parasitism, nutrient recycling, and carbon transfer. These ecological roles are distributed across autotrophic, mixotrophic, heterotrophic, and parasitic lineages, which span multiple eukaryotic supergroups and respond sensitively to environmental gradients (Bachy et al. 2022; Caron et al.
