Krill occur in all oceans of the world. They are considered keystone species near the bottom of the food chain feeding on phytoplankton. They form an important part of the marine food change for many larger animals for whom krill makes up the largest part of their diet. Krill is eaten by whales, seals, penguins, manta rays, squid and fish. Most krill species display large daily vertical migrations, thus providing food for predators near the surface at night and in deeper waters during the day.