How microbes survive in the open ocean

A drop of seawater contains almost a million small cells, including genetically diverse bacteria, archaea, and protists, as well as viruses ( 1 ). Typical microscopic views of this diversity give the impression of a dense environment (see the first figure), but they are preceded by filtration and concentration steps that mask the remarkable distances between individual cells in the ocean, where hundreds of micrometers separate cells that themselves are less than a micrometer in size. Yet despite their microscopic size and relative isolation, marine microbes catalyze chemical transformations at rates that are critical for maintaining Earth's habitability. Viewing the open-ocean microbial world through the interwoven threads of space, time, and diffusion is critical for understanding how microbial interactions shape the biogeochemical cycles of one of the largest habitats on Earth.