Their digestive system is usually visible and this is often a vivid green from the pigment of microscopic plants they have eaten. Krill usually feed on the surface of the water at night and often sink deeper in the water during the daytime. The primary food of krill is phytoplankton. There are five species of krill found in Antarctic waters. The most dominant of these species is Antarctic krill, Euphausia superba.
Antarctic krill is one of the most abundant animal species on the planet.
They are frequently found in such abundance that they color the sea a reddish brown. E superba only grow to about 60mm long and weigh more than a gram, but there is estimated to be about 500 million tons of Antarctic krill in the Southern Ocean. Krill are crustacean 'magicians'. The reason is that they can continue to change from adults into juveniles. It is estimated that Antarctic krill live for 5 to 10 years, but determining the age of the animals presents quite a problem for scientists.