Project: Characterizing and quantifying the impact of phagotrophic protists at hot spots of primary production at Axial Seamount

NSF Award Abstract:

Microorganisms are the ancestral forms of life on our planet and have been instrumental in shaping all of Earth?s environments into what they are today. In the ocean, microbial prokaryotes and eukaryotes form the foundation of marine food webs through their activity and interactions. Single-celled microbial eukaryotes (or protists) are some of the most important species on the planet, yet our understanding of how their activities influence and regulate the ocean ecosystem is poorly constrained. At deep-sea hydrothermal vents in particular, our understanding of microbial food web dynamics is incomplete without including the role of microbial eukaryotes. This project provides quantification of phagotrophic protistan grazing on the microbial communities inhabiting the highly productive diffuse vent mixing zone at hydrothermal vents, where the vent fluid-seawater interface promotes an increase in biological activity compared to the surrounding deep seawater. The results are contributing novel insights into the diversity and metabolic activities of the microbial eukaryotic community at vent fluid-seawater interfaces, establish the extent to which microbial eukaryotes impact primary production in the deep ocean by quantifying predation pressure, and estimate the amount of carbon transferred from primary producers to larger organisms. The investigators are training community college students from Cape Cod Community College by involving them in laboratory research through summer internships. The goal is to promote science, technology, engineering and math literacy among community college students through hands-on research experiences, peer-to-peer mentoring, and professional development opportunities, while also encouraging students to transfer to a four-year university, obtain a degree in a STEM subject, and continue on in a STEM field.

Grazing by microbial eukaryotes is a significant source of mortality for microbes in the oceans, thus influencing the composition of communities and serving as a major route for remineralization of organic material to all organisms. This project is quantifying the in situ rates of eukaryotic grazing on prokaryotic communities at hot spots of primary productivity in the deep sea and characterize the diversity of microbial eukaryotes, their abundance, and metabolic activities at the seafloor. The focus of the effort is at the underwater volcano Axial Seamount, home of the Ocean Observatories Initiative (OOI) Regional Cabled Array with well-characterized low-temperature diffusely venting fluids.

The two objectives of the work are to:

1. Quantify the rates and impact of phagotrophic microbial eukaryote grazing on prokaryotic communities at the seafloor in low-temperature diffuse fluid mixing zones.

2. Characterize microbial eukaryotic diversity, abundance, and metabolic gene expression at the seafloor in low-temperature diffuse fluid mixing zones.

The modular Microbial Sampler-Submersible Incubation Device (MS-SID) is being used for in situ seafloor tracer incubations and compared to shipboard incubations for the proposed grazing studies. This combination of technology provides detailed and quantitative assessments of protistan communities and establishes the extent to which microbial eukaryotes impact primary production in the deep ocean. Expected outcomes include the quantification of protistan grazing rates on bacterial and archaeal communities within the seafloor mixing zone, comparison of predation pressure at the vent-seawater interface and surrounding deep ocean water, as well as identification of key bacteriovores, fungi, and other protists and associated major active metabolic pathways within the hydrothermal mixing zones. The project is providing a significant advance in the understanding of the microbial loop in the deep ocean as current depictions of microbial ecology at hydrothermal vent sites do not typically include the role of microbial eukaryotes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.