Antarctic krill (Euphanasia superba) are a species of krill found in the Southern Ocean which surrounds Antarctica. They are distinct for being among the species with the world's greatest total biomass, probably just second to humanity, which surpassed them sometime around 2007. Their total biomass is approximately 500 million tonnes. Antarctic krill are omnipresent in the waters around Antarctica, where they enjoy relatively little competition from animals of similar size. Krill are small crustaceans.
Like many other planktonic crustaceans, krill make up their living by gobbling up little bits of phytoplankton, the plants of the sea. Whereas insects are the dominant arthropods on land, crustaceans such as Antarctic krill are the arthropod kings of the sea. They have numerous adaptations which have helped them secure their place as one of the world's species with the most biomass, including massive compound eyes, a "feeding basket" for filter feeding, a muscular telson (tail) that can be used to rapidly "lobster" away from predators, bioluminesence (the utility of which is not fully understood), swarming behavior, the ability to shrink in size from one molt to the next (to compensate for conditions of low nutrients), and many others.
In the Antarctic, Antarctic krill have been observed feeding on algae on the undersides of freezing cold icebergs or the ice sheet. Their density can approach 10,000-30,000 individuals per cubic meter. Living up to six years, Antarctic krill can grow as large as 6 cm (2.4 in), and weigh up to 2 g (0.7 oz). They are the most important prey item of the Antarctic ecosystem, consumed by fur seals, Leopard Seals, Crabeater Seals, whales, icefish, squid, penguins, albatross, and hundreds of other bird species. Due to their abundance and ecological importance, they are one of several planktonic species sometimes referred to as a "potato chip of the sea."
Unlike many other marine crustaceans, the legs of Antarctic krill do not form a jaw or claw-like structure, instead having greater similarity to the simplistic legs of many insects. To reproduce, males attach spermatophores to the area around the female genitals, which periodically releases 6,000 - 10,000 eggs. These fertilized eggs slowly descend, over the course of weeks, to kilometers below the surface, where they develop into juvenille Antarctic krill that swim back to the top. This general pattern has likely been the same for hundreds of millions of years.
Occasionally, Antarctic krill is captured by fisherman and compressed into blocks which can be used for cooking. However, yield is not nearly as high as many other crustaceans and fish, due partially to the fact that their shells contain fluorides, which can be toxic in high concentrations. Also, capturing them requires fine-grained meshes, which have high drag and frequently break. Though Antarctic krill are extremely numerous, most humans find them unexciting to eat. For now, they'll have to serve as dinner for hundreds of other species instead.