Although jellyfish may appear to be aquatic vagabonds, they don’t just drift aimlessly through the oceans. Instead, a new study has found, jellyfish can sense currents and swim against them. To measure their movements, scientists attached accelerometers to barrel jellyfish (Rhizostoma octopus) in the coastal waters of France and combined this data with visual observations from boats. In still water, the jellyfish swam in all directions, but when there was a tide, most of the jellyfish swam with or against it, the researchers report online today in Current Biology. Detecting and responding to currents isn’t easy—migrating sea turtles and birds are commonly thrown off course—and researchers don’t know how the jellies do it. The jellyfish may detect variations in water speed across their bodies when swimming near the surface, or they may use external information, like changes in Earth's magnetic field. What’s more, in computer simulations of large groups of jellyfish fighting ocean currents, the virtual jellies formed swarms that resembled “blooms” seen in the wild, made up of hundreds to millions of jellyfish. The research could help scientists predict the locations of such blooms, which can snarl up fisheries, clog water intakes for power plants, and ruin a tourist’s day at the beach.
(Video credit: Graeme Hays)