Krill are small (2 inches / 5.5 cm) shrimp-like crustaceans that are found throughout the worlds oceans. Not surprisingly, Antarctic krill (Euphausia superba) are found in the Southern Oceans surrounding Antarctica. They can form large swarms in open ocean regions, or more scattered layers under the ice edge. Krill also follow a diel vertical migration – they move up towards the ocean surface at night, and back down into deeper water during the daytime hours. Antarctic krill are filter feeders that consume algae (phytoplanton); at the bottom of the food chain, they serve as the plant grazers of their ecosystem.