The Antarctic ecosystem varies significantly due to the polar opposite conditions of summer and winter. In the summer, there is plentiful light and sunshine to power photosynthesis for algae, which transforms the ocean into a very productive ecosystem. This phytoplankton is consumed by krill, which are a key food source for many larger animals such as whales, seals, fish, and penguins. Depending on the year, gelatinous organisms called salps may dominate the lower trophic levels by competing with krill and consuming phytoplankton. Salps are not nutrient-rich, and therefore do not nourish larger animals the same way krill do.
In the winter, the Antarctic remains in near darkness. The surface of the ocean freezes over around Antarctica, providing more breeding and hunting ground for large animals like penguins and polar bears. Algae partially freezes up in the ice, while some can grow on the underside of ice sheets and provide food for hungry animals who depended on photosynthetic phytoplankton. Juvenile krill take cover under these ice sheets and feed on the ice algae to survive, while larger krill can still make it in the open ocean. These krill provide protein and fats for their predators and sustain the delicate ecosystem that has adapted to the freezing waters.
As the ocean is warming and ice is melting, the ecosystem will be changing. Whether or not some of these species will be able to adapt to the loss of ice and potential influx of invasive species is unpredictable.
Antarctic is separated by Southern Ocean from other land masses. The extreme minimum temperature has been recorded as low as -86.9 degrees Celsius and because of this extreme cold condition and windiness, the terrestrial biome is not as rich in biodiversity as the marine biome. Antarctic is surrounded by a continuous sea with relatively fast circumpolar currents. And some of the circumpolar deep water is carried to the surface which comes from eddies of the Antarctic Divergence zones. These eddies are upwelling areas where phytoplankton flourish on the additional nutrients and along with Antarctic Krill, a dominant herbivore in Southern Ocean, they serve secondary and tertiary production level.
Fauna of the Southern Ocean is not significantly rich in diversity; however, it is distinctive. Fish fauna is found to be composed of 120 species, belonging to 29 families, and the dominant fish species being Nototheniiformes. These fish are adapted to oxygen-rich and cold water. The importance of preserving the Antarctic ecosystems become important because they provide information about global system: heat budge, magnetism, atmospheric electricity, plate tectonics, ocean currents, and ocean chemistry.