Krill are considered an important trophic level connection – near the bottom of the food chain – because they feed on phytoplankton, and to a lesser extent, zooplankton, converting these into a form suitable for many larger animals for whom krill makes up the largest part of their diet including the Blue whale. One species, the Antarctic krill, Euphausia superba, makes up an estimated biomass of around 379,000,000 tons, making it among the species with the largest total biomass. Of this, over half is eaten by whales, seals, penguins, squid and fish each year, and is replaced by growth and reproduction. 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.
Sperm whales have been shown to increase the levels of primary production and carbon export to the deep ocean by depositing iron rich feces into surface waters. The feces causes phytoplankton to grow and take up more carbon from the atmosphere. When the phytoplankton dies, it sinks to the deep ocean and takes the atmospheric carbon with it. The sperm whales result in removing 200,000 tons of carbon from the atmosphere each year.