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Letter from Stephanie: Antarctic Adaptations

Part of Hall of Ocean Life.

Dear Fellow Explorers,

We are working close to the edge of the sea ice–and the wildlife is amazing! We've seen orcas, Emperor penguins, crabeater seals (they don't eat crabs), and leopard seals (they eat anything they want). We've also seen several species of birds. I'm not a bird expert, but my friend Nancy identified them as storm petrels and Antarctic terns.

As you know, working in Antarctica means dealing with some of the most extreme conditions on Earth. Our bodies are not naturally adapted to the environment here; so we need to carry our "adaptations" with us. We bring along our food, shelter, water, and warm clothing to help us survive in the harsh environment, and we have all kinds of high-tech gear to help us cope with the extremely cold, windy, dry conditions.

The plants and animals of Antarctica, however, don't have any high tech gear. They don't need it! All of them have developed interesting adaptations to survive the harsh environment, from physical to behavioral to chemical adaptations. And many of these animals' adaptations work together in incredible ways.

Physical adaptations are sometimes the easiest to spot. Many of the animals living in Antarctica have outer layers of dense fur or water-repellent feathers. Under this fur or feather layer is a thick layer of insulating fat. Many marine animals have large eyes to help them spot prey and predators in the dark waters. They are further protected by their coloration, dark backs, and light undersides. This way, they are hard to spot from above, because they blend into the dark sea floor; from below, creatures looking up see the bright light from above, and so it is hard to spot a pale belly! This adaptation helps predators stay hidden from prey and prey stay hidden from predators.

Some physical and chemical adaptations are less obvious. Orcas and penguins, for example, have circulatory systems adapted to conserve heat. Their veins wrap around their arteries, warming the blood in the arteries and saving energy. Plants and lichens that live on ice-free areas of the continent have special leaf structures that prevent loss of moisture; in the Antarctic desert, every bit of moisture counts! And because plants have to make their own food, many Antarctic plants increase the rate of photosynthesis to make food faster and at lower temperatures.

 Behavioral adaptations are another way that organisms adapt to the extreme environment of Antarctica. Some birds and whales migrate to Antarctica each summer, leaving for warmer climates during the harsh Antarctic winter. The Arctic tern is probably the most incredible example; if you are wondering why the Arctic tern is named for an area in the North Pole, you're right! The Arctic tern flies 35,000 km (21,750 miles) every year in order to catch the Arctic summer for one half of the year and the Antarctic summer for the other half!

Would you like to take a swim in water at a temperature of -2ºC ? (To compare, consider that the average swimming pool is kept at about 25ºC.) How do fish survive in such cold Antarctic waters? Antifreeze, of course! Certain fish have antifreeze proteins that lower the freezing point of their blood. These proteins attach to the small ice crystals that enter the circulatory system through the gills and prevent the ice crystals from growing. These proteins can also work on crystals that are ingested by the fish as they swim. This is a great example of chemical adaptation.

What's missing in Antarctica? A few types of organisms are notably absent–there are no amphibians, reptiles, or large trees in Antarctica. Why do you think this is? Consider the temperatures and distribution of light annually. Think about what amphibians and reptiles need. Antarctica also has no large land predators (though there are some, like the orca, or killer whale, living in the sea around Antarctica). This is good news for the seals and penguins, who live on land part of the time!

Let's take a closer look at one Antarctic organism to better understand its adaptations–and because it's an awfully cute example!

Emperor penguins spend as much as 75% of their lives in the water; most of their adaptations are related to their sea needs. They have streamlined, torpedo-shaped bodies for speedy swimming; and to heighten that streamlining, Emperor penguins keep their heads hunched into their shoulders while swimming under water. They also press their feet close to their bodies, right against their tails; this helps them steer while swimming. Notice how their physical adaptation, their body shape, works together with a behavioral adaptation, posture while swimming.

Emperor penguins dive to catch krill, squid, and fish, using their heavy, solid bones like a diver's weight belt to stay underwater. They usually catch krill in shallow dives (about 100 meters); but when krill are scarce, they are able to dive for fish to depths of 500 meters. During deep dives, an Emperor penguin's heart rate slows to a rate that is 15% lower than its resting heart; this helps the penguin conserve energy. By reducing blood flow to their extremities, Emperor penguins also conserve heat in their bodies.

Coloration is another important Emperor adaptation. The black and white coloration makes it difficult for predators (orcas and seals) to detect them in the water. Their dark upper sides camouflage them from predators looking down at the dark ocean, and their white undersides provide camouflage from predators looking up at the light ocean surface.

What about all that salt? Like other seabirds, penguins have glands in the bill to help rid the body of excess salt. After secreting salt and fluid as droplets on their bills, penguins can simply shake them off. And these glands are so effective that penguins can drink sea water!

A combination of adaptations allow Emperor penguins to thermoregulate, or control their body temperature. Overlapping feathers create a surface that is almost impenetrable to wind or water. The greasy layer over their feathers provides waterproofing; this is critical to penguins' survival in Antarctic waters, which can drop to -2.2ºC (28ºF).

Insulation is provided in two ways–tufts of down on shafts below the feathers trap air and a well-defined fat layer provides further insulation. The dark plumage of a penguin's dorsal surface (her back) absorbs heat from the Sun, which increases body temperature further.

What about all that ice? On land, Emperor penguins rest their entire weight on their heels and tail, reducing contact of their feet with the icy surface. They can also tuck their flippers in close to their bodies and shiver to generate additional heat. And they have very powerful noses! Emperor penguins are able to recapture 80% of heat escaping in their breath through a complex heat exchange system in their nasal passages.

Emperor penguins are s