ANTARCTICA WILDLIFE

Adapting to the Cold
All the organisms which live in the Antarctic area have to deal with very harsh living conditions. Under normal conditions, the temperature limits for animal activity range from slightly below 0ºC (32ºF), when body fluids freeze, to 45-50ºC (113-122ºF), when proteins coagulate and dissolved albuminoids break down. The optimum temperature for life is often close to the maximum temperature an animal can tolerate.

Climactic fluctuations demand constant adaptation, and both in water and on land animal diversity decreases where conditions approach the limit, such as in polar areas, deserts, and high mountains. Animals can be divided into two broad types - those whose internal body temperature, and therefore metabolism, varies according to the ambient temperature; and those whose internal body temperature remains relatively constant.

Variable body temperature
The invertebrates and fishes of Antarctica are of the first kind, and so are directly affected by the ambient temperature. This means that the lower their body temperature, the lower is their metabolic rate. It also means that they run the risk of freezing.

Terrestrial Animals
In Antarctica, terrestrial animals must endure tremendous variations in temperature, whereas the aquatic animals live in a more uniform environment. In order to survive freezing an insect or mite must prevent ice from forming inside its cells, and at the same time induce ice formation slowly within the rest of its body, including the contents of the gut, the blood, and the spaces between the cells.

Some of them appear to become dehydrated when exposed to low temperatures, and this causes the salts, sugars, and other constituents to concentrate in tissues, thereby reducing the freezing point.

If the cells are not ruptured during freezing the animal stands a good chance of surviving. Freeze-tolerant insects and mites produce "cryo-protectant" chemicals, such as glycerol, which allow body tissues to survive freezing by reducing the proportion of body water locked up in ice.

The marine Antarctic environment is very stable, but its temperature is close to or below the freezing temperature of fresh water. Many marine invertebrates deal with this situation by accumulating salts and organic compounds, such as glucose and amino acids, which lower the freezing point of the body fluids.

Antarctic Fishes
The fishes, like marine fishes everywhere, maintain a body salinity slightly lower than that of the sea water in which they live. Theoretically, one would therefore expect them to freeze at a slightly higher temperature than does sea water (which freezes at -1.8ºC, or 28.8ºF). Some Antarctic fishes can actually lower their freezing point by accumulating an abundance of sodium, potassium, or chloride ions, or urea, in their body tissues.

The enzyme systems of Antarctic fishes are so efficient that they are able to maintain a high level of activity even in these extremely cold waters. One family is able to synthesize glycoproteins, which act like an antifreeze by inhibiting the normal growth of ice crystals within their tissues.

The content of dissolved oxygen is so high in the cold Antarctic waters that many fishes are able to survive with little or no red blood cells. This gives them a white, or nearly colorless appearance. It is interesting to note that if these fishes come into prolonged contact with sea ice, their tissues will freeze and death results.

Constant body temperature
The birds and mammals of Antarctica, on the other hand, are of the second main type. They are able to maintain an optimal internal temperature regardless of the cold. Living at the optimum temperature means that their life processes, such as nerve transmissions, muscle contraction, digestion, etc., operate at their most efficient rates - but at a high metabolic cost. In order to maintain stable high internal body temperatures, these animals must somehow insulate themselves from the cold.

The two groups - birds and mammals - accomplish this in different ways. Air is a very poor heat conductor and is readily available as an effective insulator. The birds take full advantage of this by using feathers to retain a layer of air around their bodies. Coverts and contour feathers cover fluffy down which holds the air close to the body. Those birds with flexible wings can hold their wings close to the body and receive even more protection from wind and low temperatures.

Feathers
Birds must prevent their feathers becoming waterlogged. Water conducts heat about 25 times better than air, so it very quickly absorbs heat from the body. Most Antarctic birds have a very well developed oil gland near the base of the tail. When they preen, the birds rub this oily secretion all over their plumage in order to make it water resistant.

In addition, birds lack exposed structures, such as ears and tails, which have many blood vessels near the surface. Their legs and beaks also carry few or no blood vessels. This helps to avoid cooling the blood. Penguins are the most aquatic of the seabirds, and have evolved a modified plumage that has highly effective insulating properties.

Most birds grow feathers in narrow tracts, and then fluff them out to cover all the exposed skin. Penguins, however, have many more feathers, and almost the entire body surface is covered with a dense, tightly packed growth of feathers.

The scalelike outer parts overlap, and are almost impermeable to wind or water. And on the lower shafts grow tufts that form an insulating layer of fluffy down. Besides feathers, penguins also have a thick layer of fat or blubber just below the skin. In fact, penguins are so well insulated that they are poorly equipped to deal with warm temperatures.

The skin of their feet has more blood vessels than other birds, which they use to radiate heat when necessary. They dilate these blood vessels to lose heat on land and constrict them to conserve heat when they are in the sea. This accounts for the rosy pink feet of the nesting or roosting penguins that one sees on land. Compared with the white feet of penguins which have just come out of the water.

Insulating blubber
All the mammals found in Antarctica (except humans, of course) are aquatic. The cetaceans (whales and dolphins) protect themselves from heat loss with a thick layer of oil-rich, subcutaneous fat, or blubber. Unlike most mammals, the cetaceans have virtually no hair and so cannot use air for insulation.

They are unable to come out of the water occasionally in order to preen, clean and aerate their fur. Manatees and dugongs, which are also completely aquatic, do not have much hair. Fat serves a dual purpose since it is not only an excellent insulator, but also stores energy to allow the animals to survive when food is scarce.

But in general, animals that maintain a constant body temperature need to consume more food, to maintain heat production, when ambient temperatures are low. They need about 50 percent more food in winter than in summer, but food is harder to come by in winter. Therefore the cetaceans - along with most seals and seabirds - migrate to lower latitudes and a warmer climate during the Antarctic winter. (However, penguins and some seals do remain in Antarctic waters year round.

They simply move from the coastal areas, where they spend the summer, to the edge of the sea ice in winter.) The Antarctic seals and fur seals (collectively known as pinnipeds) have a thick layer of insulating fat, like the cetaceans, but they also have fur as an added protection against the cold. As much as 50 percent of the body weight of some seals is skin and fat.

In fact, seals have such efficient protection against heat loss that they cause little or no visible melting on the ice even after lying in one spot for several hours, and will retain a high internal body temperature many hours after death.

Warm fur coats
The fur of seals and fur seals consists of two different types of hair: long, coarse guard hairs and short, woolly underfur. Most seals have from two to five underfur hairs for each guard hair, which provides a fur coat of relatively low insulation value, so they rely mostly on their fat to prevent heat loss. Fur seals, however, have as many as 70 underfur hairs for each guard hair, and this gives them a fur coat with superb insulation.

Unfortunately, the dense, luxurious coat of fur seals was highly valued as a commercial commodity. In fact, it was the ever-widening search for new fur seal populations, as the known populations were progressively decimated, which led to the eventual discovery of Antarctica in the early 19th century.