Picoeukaryote Diversity and Spatial Distribution Patterns in the North Atlantic

Picoeukaryotes are important primary producers in the western North Atlantic, including in the oligotrophic subtropics where cyanobacteria may be numerically more abundant, but picoeukaryotes dominate the biomass. North of the Gulf Stream high nutrient concentrations, including phosphorus (P), support picoeukaryote growth and biomass accumulation. In the oligotrophic subtropical North Atlantic, primary production is limited by P availability. Using molecular analyses, we investigated the diversity and distribution patterns of different picoeukaryote lineages in samples collected from the North Atlantic across this natural P gradient. Differences in picoeukaryote community composition were primarily linked to the prasinophytes; as has been previously shown, the prasinophytes Micromonas, Bathycoccus, and Ostreococcus were found to be common picoeukaryotes to this region. In this study, we show the relative abundance was not evenly distributed as Ostreococcus dominated in the P-deficient subtropical waters. The cellular response to changes in P availability and how it differs among these picoeukaryote lineages is poorly understood. We are investigating the physiological and molecular responses of Micromonas, Bathycoccus, and Ostreococcus when grown under P-replete and P-deficient conditions. This work aids in our understanding of the metabolic mechanisms that may be driving picoeukaryote diversity and distribution patterns in the North Atlantic and hence their impact on biogeochemistry.