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The harsh climate and sparse vegetation of Antarctica’s land regions support only microscopic animals and primitive insects. Protozoa, nematodes, tardigrades, and other minute forms inhabit damp soils. Other invertebrate species include springtails and mites. The wingless midge, which grows up to 12 mm (0.47 in) long, is the largest land animal.
In contrast to the land, the Southern Ocean supports a wide variety of animal life, which all depends directly or indirectly on the phytoplankton of the surface waters. Zooplankton—including krill, copepods, arrowworms, jellyfish, fish larvae, and larval forms of bottom-dwelling starfish, bristle worms, sea anemones, and mollusks—feed on phytoplankton. Zooplankton in turn provide food for fish and squid, both of which are abundant in Antarctic waters. Members of one group of fish known as icefish have natural antifreeze to survive in the cold temperatures. Concentrated swarms of zooplankton (especially of krill and young fish), together with larger fish (especially of superfamily Notothenioidea) and squid, provide food for the seals, whales, and seabirds that are Antarctica’s major predators and most prominent animals. Some organisms grow to large size in the cold waters, including giant marine isopods related to sow bugs, giant starfish, and giant sea spiders.
Whales are plentiful in the Southern Ocean, more so since commercial whaling ended in the 1960s. Baleen whales such as blue, fin, sei, minke, humpback, and southern right whales feed mainly on krill and small fish, which they filter from the water. Among toothed whales, sperm whales and bottle-nosed whales feed mainly on fish and squid, which they catch in deep water, while killer whales (orcas) and several species of dolphins feed mainly on surface-living fish. Killer whales also prey on penguins and seals.
Several species of seals breed within the Antarctic region. Weddell and leopard seals live closest to the continental shore, while crabeater and Ross seals live mainly on pack ice. Elephant seals (the largest species) and fur seals breed mainly on the warmer fringing islands.
About 40 species of seabirds—including 7 species of penguins, 4 species of albatross, 20 species of petrels, as well as cormorants, gulls, skuas, and terns—breed within the region, mainly on islands and continental coasts. In summer, snowy petrels fly long distances over the ice to breed in inland mountain ranges. Major populations of penguins are found around Antarctica, including Adelie, emperor, chinstrap, and gentoo penguins. Emperor penguins breed in winter on sea ice. Local warming in the Antarctic Peninsula area is affecting some stocks of penguins by reducing sea ice in areas in which they breed or feed.
Large marine animals played an important role in attracting humans to Antarctica: Sealers and whalers contributed substantially to the early exploration of the Southern Ocean and coastal regions. Fur seals and southern elephant seals of the islands near the Antarctic Convergence were hunted for skins and oil throughout the 19th century until economically profitable stocks were depleted. Hunting of elephant seals continued into the 1950s. From 1904 through the 1960s whalers hunted large migratory whales (blue, fin, sei, humpback, and sperm whales) for oil in Antarctic waters from whaling stations on several Antarctic islands and from floating factory ships. Beginning in the 1960s concern that seals and whales would be hunted to extinction prompted several measures to protect surviving populations.