Antarctic Marine Ecosystems
For the numerous species of birds, seals, whales, and other animals, the marine ecosystem is the keystone of life in the polar waters. For the sturdy animals that can survive this windswept environment, the nutrient-rich waters of Antarctica provide an all-you-can-eat buffet.
Among the pack ice and frozen waters of Antarctica, a marine ecosystem teeming with life supports the robust and durable creatures that call this frigid environment their home. Since the land is covered annually or semi-annually with snow and ice, the animals that live in these polar waters must depend on the ocean for their food, and it does not disappoint.
The Antarctic Convergence
At the southernmost part of the Atlantic, Pacific, and Indian Oceans, there is a narrow 25-mile (40 km) wide stretch of water known as the Antarctic Convergence, which marks the northern limit of the southern ocean. Along this polar front, the cold water is drawn to the surface, making possible the whole marine ecosystem that thrives here.
Some of the smallest invertebrates in the world – form the base of most Antarctic diets for small birds like the snow petrel to the biggest of all animals, the blue whales, and everything in between. The winds and cold water here cause upwelling to occur, which fills the surface levels of the ocean with the nutrient-rich waters from the depths. This brings with it a wealth of phytoplankton that forms the primary diet of the krill, which in turn form the bottom of the food chain for the bigger animals.
Other invertebrates & fish
Bigger crustaceans, like crabs and lobsters, are scarce to be found in the Antarctic waters, however, smaller invertebrates turn these sub-zero waters into a vibrant seascape that contrasts with the expansive white deserts above. Divers who have been lucky enough to explore these waters even compare the colorful marine life to that of coral reefs.
The seafloor is characterized by a rainbow of sea stars, urchins, and carnivorous worms that can be meters long. Although these creatures all move very slowly, their ability to find and digest food makes them an unlikely predator in a sea where so few others can survive.
Just like freezing food allows it to last longer, the freezing waters here help extend the longevity of much of the polar marine life. The phenomenon of gigantism, in which certain creatures are much larger than their cousins in other parts of the world, also seems to help these invertebrates survive the bitter cold.
Across the board, this is a cradle for Darwin’s theory of natural selection, as only the fittest of sea creatures have adapted to life here. The most common of the polar fish are the Notothenids (Antarctic Cod), which produce their own natural antifreeze to withstand the cold. Another trick to surviving the water is staying away from the ice itself – since ice needs a surface to crystallize, many fish swim in the dark depths of the ocean where water is well below freezing but has not turned to ice.
Several species of fish even lack hemoglobin in their blood, which indirectly allows them to take advantage of the high volume of oxygen dissolved in the cold water to help the non-viscous blood flow more quickly through their bodies.