The wildlife of Antarctica are extremophiles, having adapted to the dryness, low temperatures, and high exposure common in Antarctica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.
There is relatively little diversity in Antarctica compared to much of the rest of the world. Terrestrial life is concentrated in areas near the coast. Flying birds nest on the milder shores of the Peninsula and the subantarctic islands. Eight species of penguins inhabit Antarctica and its offshore islands. They share these areas with seven pinniped species. The Southern Ocean around Antarctica is home to 10 cetaceans, many of them migratory. There are very few terrestrial invertebrates on the mainland, although the species that do live there have high population densities. High densities of invertebrates also live in the ocean, with Antarctic krill forming dense and widespread swarms during the summer. Benthic animal communities also exist around the continent.
Over 1,000 fungi species have been found on and around Antarctica. Larger species are restricted to the subantarctic islands, and the majority of species discovered have been terrestrial. Plants are similarly restricted mostly to the subantarctic islands, and the western edge of the Peninsula. Some mosses and lichens however can be found even in the dry interior. Many algae are found around Antarctica, especially phytoplankton, which form the basis of many of Antarctica's food webs.
Human activity has caused introduced species to gain a foothold in the area, threatening the native wildlife. A history of overfishing and hunting has left many species with greatly reduced numbers. Pollution, habitat destruction, and climate change pose great risks to the environment. The Antarctic Treaty System is a global treaty designed to preserve Antarctica as a place of research, and measures from this system are used to regulate human activity in Antarctica.
Environmental conditions
Around 98% of continental Antarctica is covered in ice up to thick. Antarctica's icy deserts have extremely low temperatures, high solar radiation, and extreme dryness. Any precipitation that does fall usually falls as snow, and is restricted to a band around from the coast. Some areas receive as little as of precipitation annually. The coldest temperature recorded on Earth was at Vostok Station on the Antarctic Plateau. Organisms that survive in Antarctica are often extremophiles.
The dry interior of the continent is climatically different from the western Antarctic Peninsula and the subantarctic islands. The Peninsula and the islands are far more habitable; some areas of the peninsula can receive of precipitation a year, including rain, and the northern Peninsula is the only area on the mainland where temperatures are expected to go above in summer. The subantarctic islands have a milder temperature and more water, and so are more conducive to life.
The surface temperature of the Southern Ocean varies very little, ranging from to . During the summer sea ice covers of ocean. The continental shelf surrounding the mainland is wide. The depth of the seafloor in this area ranges from , with an average of . After the shelf, the continental slope descends to abyssal plains, deep. In all these areas, 90% of the seafloor is made up of soft sediments, such as sand, mud, and gravel.
Ozone depletion and the presence of a seasonal ozone hole above Antarctica exposes the area to high levels of ultraviolet radiation, although the hole is usually largest when snow and ice is more widespread, reducing overall impact.
Animals
At least 235 marine species are found in both Antarctica and the Arctic, ranging in size from whales and birds to small marine snails, sea cucumbers, and mud-dwelling worms. The large animals often migrate between the two, and smaller animals are expected to be able to spread via underwater currents. However, among smaller marine animals generally assumed to be the same in the Antarctica and the Arctic, more detailed studies of each population have often—but not always—revealed differences, showing that they are closely related cryptic species rather than a single bipolar species. Antarctic animals have adapted to reduce heat loss, with mammals developing warm windproof coats and layers of blubber.
Antarctica's cold deserts have some of the least diverse fauna in the world. Terrestrial vertebrates are limited to subantarctic islands, and even then they are limited in number. Antarctica, including the subantarctic islands, has no natural fully terrestrial mammals, reptiles, or amphibians. Human activity has however led to the introduction in some areas of foreign species, such as rats, mice, chickens, rabbits, cats, pigs, sheep, cattle, reindeer, and various fish. Invertebrates, such as beetle species, have also been introduced.
The benthic communities of the seafloor are diverse and dense, with up to 155,000 animals found in . As the seafloor environment is very similar all around the Antarctic, hundreds of species can be found all the way around the mainland, which is a uniquely wide distribution for such a large community. Polar and deep-sea gigantism, where invertebrates are considerably larger than their warmer-water relatives, is common in this habitat. These two similar types of gigantism are believed to be related to the cold water, which can contain high levels of oxygen, combined with the low metabolic rates ("slow life") of animals living in such cold environments.
Birds
The rocky shores of mainland Antarctica and its offshore islands provide nesting space for over 100 million birds every spring. These nesters include species of albatrosses, petrels, skuas, gulls and terns. The insectivorous South Georgia pipit is endemic to South Georgia and some smaller surrounding islands. Ducks, the South Georgia pintail and Eaton's pintail, inhabit South Georgia, Kerguelen and Crozet.
The flightless penguins are almost all located in the Southern Hemisphere (the only exception is the equatorial Galapagos penguin), with the greatest concentration located on and around Antarctica. Four of the eighteen penguin species live and breed on the mainland and its close offshore islands. Another four species live on the subantarctic islands. Emperor penguins have four overlapping layers of feathers, keeping them warm. They also reduce heat loss with countercurrent heat exchange systems throughout their body to cool blood as it reaches extremities like the feet. They are the only Antarctic animal to breed during the winter.
Fish Compared to other major oceans, there are few fish species in few families in the Southern Ocean. The most species-rich family are the snailfish (Liparidae), followed by the cod icefish (Nototheniidae) and eelpouts (Zoarcidae). Together the snailfish, eelpouts and notothenioids (which includes cod icefish and several other families) account for almost of the more than 320 described fish species in the Southern Ocean. Tens of undescribed species also occur in the region, especially among the snailfish. If strictly counting fish species of the Antarctic continental shelf and upper slope, there are more than 220 species and notothenioids dominate, both in number of species (more than 100) and biomass (more than 90%). Southern Ocean snailfish and eelpouts are generally found in deep waters, while the icefish also are common in shallower waters. In addition to the relatively species-rich families, the region is home to a few species from other families: hagfish (Myxinidae), lamprey (Petromyzontidae), skates (Rajidae), pearlfish (Carapidae), morid cods (Moridae), eel cods (Muraenolepididae), gadid cods (Gadidae), horsefish (Congiopodidae), Antarctic sculpins (Bathylutichthyidae), triplefins (Tripterygiidae) and southern flounders (Achiropsettidae). Among fish found south of the Antarctic Convergence, almost 90% of the species are endemic to the region.
Icefish
Cod icefish (Nototheniidae), as well as several other families, are part of the Notothenioidei suborder, collectively sometimes referred to as icefish. The suborder contains many species with antifreeze proteins in their blood and tissue, allowing them to live in water that is around or slightly below . Antifreeze proteins are also known from Southern Ocean snailfish and eelpouts.
There are two icefish species from the genus Dissostichus, the Antarctic toothfish (D. mawsoni) and the Patagonian toothfish (D. eleginoides), which by far are the largest fish in the Southern Ocean. These two species live on the seafloor from relatively shallow water to depths of , and can grow to around long weighing up to , living up to 45 years. The Antarctic toothfish lives close to the Antarctic mainland, whereas the Patagonian toothfish lives in the relatively warmer subantarctic waters. Toothfish are commercially fished, and illegal overfishing has reduced toothfish populations.
Another abundant icefish group is the genus Notothenia, which like the Antarctic toothfish have antifreeze in their bodies.
An unusual species of icefish is the Antarctic silverfish (Pleuragramma antarcticum), which is the only truly pelagic fish in the waters near Antarctica.
Mammals
Six pinniped species inhabit Antarctica. The largest, the Southern elephant seal (Mirounga leonina), can reach up to and over long, while females of the smallest, the Antarctic fur seal (Arctophoca gazella), reach only . These two species live north of the sea ice, and breed in harems on beaches. The other four species can live on the sea ice. Crabeater seals (Lobodon carcinophagus) and Weddell seals (Leptonychotes weddellii) form breeding colonies, whereas leopard seals (Hydrurga leptonyx) and Ross seals (Ommatophoca rossii) live solitary lives. Although these species hunt underwater, they breed on land or ice and spend a great deal of time there, as they have no terrestrial predators.
The four species that inhabit sea ice are thought to make up 50% of the total biomass of the world's seals. Crabeater seals have a population of around 15 million, making them one of the most numerous large animals on the planet. The New Zealand sea lion (Phocarctos hookeri), one of the rarest and most localized pinnipeds, breeds almost exclusively on the subantarctic Auckland Islands, although historically it had a wider range. Out of all permanent mammalian residents, the Weddell seals live the furthest south.
There are 10 cetacean species found in the Southern Ocean; six baleen whales, and four toothed whales. The largest of these, the blue whale (Balaenoptera musculus), grows to long weighing 84 tonnes. Many of these species are migratory, and travel to tropical waters during the Antarctic winter. Orcas, which do not migrate, nonetheless regularly travel to warmer waters, possibly to relieve the stress the temperature has on their skin.
Land invertebrates
Most terrestrial invertebrates are restricted to the subantarctic islands. Although there are very few species, those that do inhabit Antarctica have high population densities. In the more extreme areas of the mainland, such as the cold deserts, food webs are sometimes restricted to three nematode species, only one of which is a predator. Many invertebrates on the subantarctic islands can live in subzero temperatures without freezing, whereas those on the mainland can survive being frozen.