In the eyes of the casual observer Antarctica may appear to be a desolate place. There is certainly some truth in that view: the Biosphere essentially ends on the coastlines of Antarctica. But on closer inspection we learn that this incredibly severe environment harbors a surprising diversity of life. The trick is to look underwater, where conditions are fairly constant and not nearly as harsh as on land. The sea floor is literally carpeted with plants and animals (Image 1, life on the bottom). Many are exotic and unique, but overall the marine fauna of Antarctica is not unlike those in other oceans (Image 2, anemone).
Well over 100 species of fish live in these icy waters (Image 3, Parachaenichthys). Most are rather sluggish and blandly colored, but physiologically they show some remarkable adaptations not found in their temperate and tropical counterparts. Some lack blood cells and hemoglobin, the substance that makes our blood red and is responsible for carrying oxygen. The body of these "ice fish" is pale, and their blood clear. By not producing hemoglobin they apparently save energy, sacrificing swimming speed for the sake of economy. All fishes living in the Antarctic must somehow keep their body fluids from freezing in the sub-freezing (-2 to 0 C) waters. They deal with this problem by synthesizing antifreeze substances called glycopeptides. These chemicals work by preventing ice crystals from growing inside the bodies of these animals. In the absence of ice crystallization, some Antarctic fish can withstand temperatures as low as -7 Celsius. Temperatures much above freezing kill them quickly.
Some animals that we see in the Antarctic seas are rarely found in other parts of the world. Brachiopods, for example, (Image 4, a cluster of Lyothirella; superficially resemble clams but are in a different phylum or branch of life), were once a ubiquitous resident of the oceans, but a couple hundred million years ago, for reasons that are still unclear, they began to disappear from the fossil record. Today only a few species manage to scrape out a living, having been supplanted by clams and other similar animals over the eons. In the Antarctic Peninsula, one brachiopod species is extremely common, living attached to rocks and filtering the sea water for their food. These sedentary animals would be a tasty morsel for a variety of predators, but they use a secret weapon: a number of chemicals in their bodies tare quite noxious and make them unpalatable to any would-be assailant.
The anti-predator defense in brachiopods is an especially common strategy in the Antarctic fauna. Sponges (Image 5 finger sponge; relatively primitive colonial animals) produce all sorts of toxic chemicals to ward off predators . Sea slugs (Image 6, dorid nudibranch) look quite defenseless as they slowly lumber along on the sea floor but also employ powerful chemical defenses, and they too are left alone. Perhaps the most "offensive" of all the invertebrates in this area are the ribbon worms (Image 7, Parborlasia). These animals grow to more than 6 ft in length and live throughout the Antarctic, yet no predator would dare eat one. One doesn't need to get close to a ribbon worm to understand why! They produce a mucus that is both pungent and noxious, and which leaves a foul smell on the hands of any scientist who has the misfortune of coming into close contact with these animals.
While we are on the subject of giant invertebrates, it is worth mentioning another interesting characteristic of Antarctic animals: giantism. A great example of this phenomenon is the sea spider. Sea spiders are found all over the world, but they normally grow only about as big as your pinkie nail. Antarctic sea spiders like the one in this image (image 8, Collesindeis) can grow as large as 12 inches from arm tip to arm tip and are considered veritable giants of their kind! Why some animals should be so much bigger in the Antarctic is still a mystery. One ecological explanation is that the scarcity of predators allows animals to live for decades, and thus grow to be giants.
Since there are few fishes in the Antarctic, the main predators are invertebrates. Among the invertebrates, the sea stars are the most successful. Sea stars in these waters come in all shapes, colors and sizes. By far the most formidable predator among the sea stars is the sunflower star (Image 9, Labidiaster). This large, active animal can catch just about everything, including fish, using the hydraulics of it's vascular system to pounce on prey. Other stars tend to feed on sick or dying prey. The purple Odontaster is a colorful example of this feeding behavior (Image 10).
true rulers of the Antarctic invertebrate fauna are the crustaceans. Ironically,
some of the most common crustaceans elsewhere are virtually absent from
antarctic waters: crabs lobsters, large shrimp. Scientists are at a loss
to explain this mystery. Other crustaceans are extremely common. Krill,
which resemble small shrimp, form swarms that may hold millions of animals!
Many marine animals, including seals, penguins, and especially the baleen
whales, depend on this plentiful food supply. Also common here are the
marine scuds (Image 4, brown stuff on sponge)
and the sow bugs (we call them "cockroaches"). They are actually not insects,
but crustaceans related to crabs, lobsters, and to your run-of-the-mill
garden pill bugs. There is one species of sow bug here that reaches gigantic
proportions (Image 11, Glyptonotus)
and easily wins the title of most intimidating invertebrate in the Antarctic
(doubters among you can refer to the last photo in our previous entry).
Fortunately, this imposing morphology belies a rather timid, passive behavior.
As with life in general, the truth about Antarctic invertebrates is usually
hidden below the surface.
|Last Updated: 10/28/97|