Antarctica

While the Arctic region teems with life, the Antarctic continent is nearly barren due to the persistently cold and dry climate. Plants that grow in the region reflect this climate and geology. The pearlwort (Colobanthus quitensis) and grass (Deschampsia antarctica) are the only two flowering plants on the continent. Both grow in a small area on or near the warmest part of the continent, the Antarctic Peninsula. Larger plants include mosses and lichens (a combination of algae and fungi) found along the coast and on the peninsula. Green, nonflowering liverworts live on the western side of the peninsula. Brightly colored snow algae often form on top of the snow and ice, coloring it red, yellow, or green.

A few hardy organisms live on rocks in the dry valleys; these are primarily lichens that hide inside the porous orange sandstone. These lichens, called cryptoendoliths or "hidden in rock," use up more than 99.9% of their photosynthetic productivity simply to stay alive. In contrast, a typical plant uses 90% for survival. Ironically, the lichens found in these valleys are among the longest-living organisms on earth. The dry valleys also host pockets of algae, fungi, and bacteria between frozen rock crystals; these give scientists clues about how life might survive on a frozen planet like Mars.

Few creatures can survive Antarctica's brutal climate. Except for a few mites and midges, native animals do not exist on Antarctica's land. Life in the sea and along the coast of Antarctica and its islands, however, is often abundant. A wide variety of animals make the surrounding waters their home, from zooplankton to large birds and mammals. A few fish have developed their own form of antifreeze over the centuries to prevent ice crystals from forming in their bodies, while others have evolved into cold-blooded species to survive the cold.

The base of Antarctica's marine food chain is phytoplankton, which feed on the rich nutrients found in coastal waters. The zooplankton feed on the phytoplankton, which are in turn consumed by the native fish, birds, and mammals. Antarctic krill (tiny shrimplike creatures about 1.5 in [4 cm] long) are the most abundant zooplankton and are essential to almost every other life form in the region. They swim in large pools and look like red patches on the ocean. At night, their crusts shimmer like billions of fireflies beneath the sea. Because of their abundance, krill have also been explored as a potential food source for humans.

Among the whales that make the southern oceans their home for at least part of the year are the blue, fin, sei, minke, humpback, and southern right whales. Known as baleen whales, this whale group has a bristly substance called baleen located in plates in their mouths that filter food such as krill from the water. In fact, the blue whale is the largest animal ever known to have lived on Earth. The blue whale eats 3 tons (6,000 pounds or 2.7 metric tons) of krill each day and has been measured to weigh up to 180 tons (163,000 kg) and span 124 ft (38 m) in length. After it was discovered in the 1800s, the blue whale was heavily hunted for its blubber, which was melted into oil for fuel. While scientists believe more than 200,000 existed before whaling, there are as few as 1,000 blue whales today. All baleen and toothed whales are now protected from hunting by international agreements.

Two toothed whales also swim in Antarctic waters, the sperm and the orca or killer whale. The sperm whale is the larger of the two, measuring as long as 60 ft (18 m) and weighing as much as 70 tons (63,500 kg). It can dive down to 3,300 ft (1,006 m).

More than half the seals in the world live in the Antarctic—their blubber and dense fur insulate them from the cold. Five species of true or earless seals live in the region, the Weddell, Ross, leopard, crabeater, and elephant. The Weddell seal is the only one that lives in the Antarctic year-round, on or under the ice attached to the continent in the winter. Using their sawlike teeth to cut holes in the ice for oxygen, they can dive down to 2,000 ft (610 m) to catch fish and squid. The seals use a complex system to control their bodies' oxygen levels, which allows them to dive to such depths and stay underwater for as long as an hour.

The Ross seal, named for English explorer James Ross, is quick underwater and catches fish easily with its sharp teeth. It lives on the thickest patches of ice and is the smallest and least plentiful of the species. Leopard seals are long and sleek and are fierce predators, living on the northern edges of pack ice and in the sea or near penguin rookeries, where they eat small penguins and their eggs as well as other seals. Crabeater seals are the most plentiful species of seal on Earth, with an estimated 40 million or more in the Antarctic region alone. Elephant seals are the largest species of seal, live on the sub-antarctic islands, and eat squid and fish. Unlike most seals, the males are much larger than the females. All five seal species are now protected under international law from hunting, which almost wiped out the Ross and elephant seals in the 1800s. One other type of seal, the southern fur seal, is also plentiful on Antarctica. It has visible ears and longer flippers than the true seals, which makes it much more agile on land as well as in the water.

Several seabirds make the Antarctic their home, including 24 species of petrels, small seabirds that dart over the water and nest in rocks along the shore. Examples include the albatross (a gliding bird with narrow, long wings that may live up to 40 years), the southern giant fulmar, dove prion, and snow petrel. Shore birds that feed in the shallow waters near the shoreline include the blue-eyed cormorant, the Dominican gull, and the brown skua, which eats the eggs and young of other birds. The Arctic tern is the world's best at long-distance flying, because it raises its young in the Arctic but spends the rest of the year in the Antarctic, a distance of over 10,000 mi (16,090 km). Land birds include the wattled sheathbill, South Georgia pintail, and South Georgia pipit.

Of all the animals, penguins are the primary inhabitants of Antarctica. Believed to have evolved 40–50 million years ago, they have oily feathers that provide a waterproof coat and a thick layer of fat for insulation. Penguins' bones are solid, not hollow like those of most birds that allow them to fly. While solid bones prevent penguins from flying, they add weight and make it easier for penguins to dive into the water for food. Because predators cannot live in the brutally cold climate, penguins do not need to fly; thus, their wings have evolved over the centuries to resemble flippers or paddles.

Seven of the 18 known species of penguins live on the Antarctic: the Adelie and emperor (both considered true Antarctic penguins because they live on the continent), the chinstrap, gentoo, macaroni, rockhopper, and king penguins. The Adelie is the most plentiful species of penguin and can be found over the widest area of the continent. They spend their winters on the pack ice away from the continent, then return to land in October to nest in large rookeries or colonies along the rocky coasts. The emperor penguin is the largest species of penguin; it is the only Antarctic bird never to set foot on land, and it breeds on sea ice attached to the mainland. The most popular type of penguin for zoos, emperor penguins are 4 ft (1.2 m) tall and can weigh up to 80 lb (30 kg). They are the hardiest of all the animals that inhabit the Antarctic, staying throughout the year while other birds head north to escape the brutal winter. They breed on the ice surface during the winter months because their immense size requires a longer incubation period. This schedule also ensures that the chicks will hatch in July or early spring in the Antarctic, providing the most days for the chicks to put on weight before the next winter's cold arrives.

The female lays one egg on the ice, then walks up to 50 mi (80 km) to open sea for food. When she returns, filled with food for the chick, the male—who has been incubating the egg atop the ice during the coldest winter months—makes the same trek out to sea to restore its body weight, which may drop by 50% during this period. The parents take turns traveling for food after the chick has hatched.

Because the emperor penguin is one of the few species that lives on Antarctica year-round, researchers believe it could serve as an indicator to measure the health of the Antarctic ecosystem. The penguins travel long distances and hunt at various levels in the ocean, covering wide portions of the continent. At the same time, they are easily tracked because the emperor penguins return to their chicks and mates in predictable ways. Such indicators of the continent's health become more important as more humans travel to and explore Antarctica and as other global conditions are found to affect the southernmost part of the world.