Gabrielle Rocap is a biological oceanographer who studies the evolution and ecology of marine bacteria. She works in diverse environments—everywhere from Puget Sound to the South Atlantic Ocean—and uses physiological, molecular, and computational techniques to work with the different species of phytoplankton that drive the bulk of global primary production. She is also working to understand the role that viruses might play in the outbreak or suppression of toxic algal blooms. The questions at the root of her many projects are: How does genetic diversity arise in marine microbial populations? How is it maintained? And how does it influence ecological success?