Collaborative Research: Assessing denitrification and other strategies for planktic foraminiferal survival under dysoxic conditions

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As the oxygen levels in the world’s oceans are decreasing, the coastal areas that cannot support life (‘dead zones’) and open ocean oxygen minimum zones (OMZs) are increasing. The expansion of deoxygenation has significant ecological consequences and impacts global climate through biologically-mediated carbon and nitrogen cycling changes. Understanding the survival strategies and biogeochemical contributions of organisms that tolerate very low-oxygen environments is thus critical. This project investigates the strategies that free-floating foraminifera, an important group of eukaryotic single-celled organisms, use to survive within the OMZ. A particular focus is whether foraminifera in the water column can respire nitrogen like foraminifera species within the ocean floor and contribute significantly to global nitrogen cycling. This project supports two early-career female scientists, including one from an underrepresented group in geosciences, and at sea and laboratory training for one graduate student and several undergraduates at North Carolina State University. In addition, science outreach includes a Science-through-Art exhibition in collaboration with a professor at the University of Iowa and a multimedia multi-sensory teaching module for freshman high school students in Falmouth, MA, to share aspects of the project about marine species living in deoxygenated settings.The overall goal of this project is to elucidate the biological strategies planktic foraminifera use to thrive in dysoxic and anoxic environments in the pelagic ocean. The project tests three interrelated hypotheses: 1. OMZ-dwelling planktic foraminifera are capable of performing denitrification; 2. Denitrification is widespread among planktic foraminifera, within and beyond OMZ-affiliated taxa; 3. Planktic foraminifera capable of nitrate respiration do so regardless of macroenvironmental oxygen concentrations. Samples from depth-stratified net tows (MOCNESS) along a north-south transect above and within the Northeastern Pacific OMZ are used to quantify the abundance and distribution of planktic foraminifera across oxygen gradients and to understand how planktic foraminifera tolerate low-oxygen environments. Metatranscriptomic analyses of foraminifera species thought to live in variable oxygen environments are used to test for the presence of denitrification pathways. Additional shipboard incubations of individuals allow direct testing for denitrification. These analyses are assessing how widespread denitrification potential is among planktic foraminifera and under what oxygen concentrations foraminifera may actively denitrify. Additionally, analysis of preserved foraminifera are determining cytoplasm nitrate and nitrogen isotope content and cytological studies to elucidate ultrastructure to reveal other potential survival strategies (i.e., symbiosis).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.