Marine fungi (mycoplankton) have long been overlooked in the ocean, yet recent evidence reveals their ubiquitous presence and active roles in the global ocean. This talk synthesizes recent advances that establish pelagic fungi as ecologically significant components of marine microbial communities, presenting the current state of knowledge. In a recent global assessment of pelagic fungal biomass combining multiple quantification techniques, we showed that fungi contribute 0.32 Gt C to open-ocean biomass—exceeding that of archaea. Complementary physiological characterization of cultured isolates reveals broad environmental tolerances and metabolic traits that support their widespread distribution. Additionally, a global-ocean multi-omics analysis of fungal-affiliated peptidases demonstrated that fungi are active contributors to protein degradation, with distinct depth partitioning between surface and mesopelagic layers that contrasts with prokaryotic patterns, suggesting distinct ecological niches. Collectively, this presentation will show that pelagic fungi are not merely transient residents but active and substantial contributors to microbial biomass and marine biogeochemical cycles, warranting their inclusion in ocean biogeochemical models.
