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 4.7 kilometres (2.9 mi) 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 300 kilometres (186 mi) from the coast. Some areas receive as little as 50 mm (2.0 in) of precipitation annually. The coldest temperature recorded on Earth was −89.4 °C (−128.9 °F) 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 900 mm (35.4 in) of precipitation a year, including rain, and the northern Peninsula is the only area on the mainland where temperatures are expected to go above 0 °C (32 °F) 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 1 °C (33.8 °F) to 1.8 °C (35.2 °F). During the summer sea ice covers 4,000,000 square kilometres (1,500,000 sq mi) of ocean. The continental shelf surrounding the mainland is 60 to 240 kilometres (37 to 149 mi) wide. The depth of the seafloor in this area ranges from 50 to 800 metres (164 to 2,625 ft), with an average of 500 metres (1,640 ft). After the shelf, the continental slope descends to abyssal plains, 3,500–5,000 metres (11,483–16,404 ft) 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 1 square metre (10.8 sq ft). 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
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