The Impact of Phagotrophic Protists at Hot Spots of Primary Production in the Deep Sea

Our current understanding of microbial food web dynamics and ecology at deep-sea hydrothermal vent ecosystems is incomplete without including the role of microbial eukaryotes. Vent fluids mixing with seawater at hydrothermal vent systems supports hotspots of biological activity by microbial chemosynthetic primary producers. Microbial eukaryotic trophic interactions, especially in the form of grazing, undoubtedly impact the distribution and richness of the resident bacteria and archaea, as well as the flow of carbon in these ecosystems. Here, we took a qualitative and quantitative approach to explore the diversity and distribution of protists at deep-sea hydrothermal vent sites and measure the predation pressure that protistan grazers exert on vent bacteria and archaea. Sequence surveys of protistan biodiversity, at both Axial Seamount (submarine volcano on Juan de Fuca Ridge) and Gorda Ridge (spreading center) hydrothermal vent ecosystems, revealed a diverse assemble of putative grazers, parasites, and symbiotic hosts. Results from grazing experiments conducted with mixed fluids from Gorda Ridge revealed protistan grazing on vent bacteria and archaeal communities. Together, this work provides novel insight into underexplored protist communities at hydrothermal sites and relevant trophic interactions which form the foundation of deep-sea marine food webs and mediate carbon transfer to higher trophic levels.