Irvine, Calif., & East Boothbay, Maine, Nov. 24, 2014 — Single-cell phytoplankton in the ocean are responsible for roughly half of global oxygen production, despite vast tracks of the open ocean that are devoid of life-sustaining nutrients. While phytoplankton’s ability to adjust their physiology to exploit limited nutrients in the open ocean has been well documented, little is understood about how variations in microbial biodiversity – the number and composition of marine microbes – affects global ocean function.