Corals may whip up whirlpools to spin specks of food in and bits of waste out. Scientists had known that hairlike bristles, or cilia, on coral help sweep nutrients in, but the purpose of bristles lining the valleys between coral polyps had been more mysterious. Using video microscopy, MIT environmental engineer Vicente Fernandez and colleagues recorded two short clips of Pocillopora damicornis coral in seawater, taken 90 minutes apart. The researchers traced particle paths (gold) and coral polyp locations (pink) captured in the first video and the paths and polyps (aqua and purple) recorded in the second, then combined them. The resulting image, which won the 2013 International Science & Engineering Visualization Challenge in photography, shows that the corals shifted position over time, but the vortex swirling in the 3-millimeter gap between them endured. These steady whirlpools might keep corals healthy, Fernandez says, and the between-polyp bristles probably keep water twirling.