Krill are a small shrimp-like crustacean that can be found in all the oceans of the world. There are over 80 different species of krill and most are only 1-2 cm (0.4–0.8 in) long. Krill usually form large swarms where up to 60,000 individual krill can be found per cubic meter. Their small size means that they are very slow-moving, although they can cover 2 to 3 body lengths per second. Krill are a very important part of the food chain and are eaten by whales, penguins, seals, squid and fish. In Japan and Russia krill are caught for human consumption. They are also caught for feeding fish, to be used for bait and for use in some pharmaceutical products. We now know that krill are an important food for many marine species, but what do these tiny animals eat for themselves?
What do krill eat?
Most species of krill are filter feeders, which means that they strain food particles from seawater. The main diet of the krill is phytoplankton, which are plant-based microscopic organisms. The main phytoplankton eaten by krill are diatoms, which are algae that consist of only one cell. Many species of krill also eat smaller amounts of zooplankton, which are tiny organisms found in seawater. It is for this reason that marine biologists believe krill to be omnivorous (an animal that eats both plants and animals), but there is at least one species that is carnivorous (they prey on fish larvae and zooplankton).