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The Southern Ocean ecosystem

The Southern Ocean covers a vast area north of the Antarctic mainland. The northern limit of the Southern Ocean is often defined along the Antarctic convergence also known as the Antarctic Polar Front where cold northward flowing Antarctic waters meet the warmer sub-Antarctic waters and acts as an oceanographic barrier towards the great oceans further north. The most significant oceanographic feature of the Southern Ocean is the Antarctic Circumpolar Current. This is the strongest current in the world moving from the west to east driven by strong westerly winds.

The trophic dynamics of the biological communities in the Southern Ocean is characterized by the often exceptionally large steps between the trophic levels. This is exemplified by Antarctic krill (Euphausia superba) which consumes microscopic phytoplankton and in turn may be consumed by a whale. Two grazers dominate in the Southern Ocean: the Antarctic krill and the salp (primarily Salpa thompsoni), which is a free-floating tunicate. Although the species to a certain degree overlap in distribution, the salps tend to occupy lower-production regions and tolerate warmer waters than the Antarctic krill.

The fish fauna in the Antarctic is characterized by the domination of a few species groups, notably the Antarctic cod or Notothenoids. Among the Notothenoids are the icefish with its unique adaptation of lack of haemoglobin in the blood. Among these is the commercially harvested mackerel icefish (Champsocephalus gunnari).

Whales, seals, penguins and flying seabirds are very notable components of the Antarctic ecosystem. To a large extent they define people’s perception of the Antarctic wildlife, and a secure food availability for such charismatic megafauna is a key topic for ensuring a sustainable harvest in the Southern Ocean, in particular of krill. 

What is an ecosystem?

Ecosystems are often described in terms of energy transfer between levels of the food chain. Behind the energy transfer, however, a life or death struggle between predators and prey is taking place. This struggle, in which every individual tries to make the most of itself by spreading its genes, results in what we call the “interplay of nature”. This interplay is fascinating, both as a field of study and as a management problem.

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