Heterotrophic microbes are crucial in ocean carbon cycling. While a significant body of literature examines heterotrophic bacterioplankton and phytoplankton communities, much less is known about the diversity and ecology of micro-eukaryotic heterotrophs (e.g., fungi and fungus-like protists) in the global ocean. As a major group of heterotrophic micro-eukaryotes, Labyrinthulomycetes, also known as fungus-like protists, are ubiquitous unicellular protists in marine environments. Our decade-long efforts have revealed that their biomass approaches and/or occasionally surpasses that of bacterioplankton. Beyond their significant contribution to secondary production, they play critical ecological roles in degrading organic matter and providing higher trophic levels with ω-3 polyunsaturated fatty acids (PUFAs). This presentation will discuss their ecotype differentiation and spatial and temporal distribution patterns in responding to the environmental conditions in both the coastal and open oceans. With representatives of cultural communities, we will also present our recent discoveries of their nutritional models and fascinating genomics features of different ecotypes. Toward the end, efforts will be dedicated to elaborating the “Blue Carbon Accelerator” hypothesis in addressing their ecological role in ocean carbon cycling and sequestration.

heterotrophic micro-eukaryotes, unicellular protists, carbon cycling, functional ecology