Zooplankton are those animals which are unable to swim effectively against the horizontal currents of the ocean; instead, they drift in the ocean, some species browsing on phytoplankton, others consuming the browsers. Although most zooplankton species are circumpolar in distribution, they frequently show centers of concentration at different depths or in different latitudes.
The circumpolar distribution of many plankton species seems to be lopsided, with large populations in the Scotia/Weddell Sea region and thinner bands around the rest of the continent. As with the phytoplankton stocks, waters south of the Antarctic Convergence are richer in zooplankton than sub-Antarctic waters to the north.
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Antarctic zooplankton also exhibit seasonal variations. In summer, they are more plentiful in coastal than in open ocean waters, while in winter they are found at greater depths. The dominant organisms in Antarctic zooplankton are the "copepods" and the "euphausiids", such as krill. In the past krill supported enormous stocks of whales. Some researchers believe that the 3-5 cm sized krill are the most numerous animal species on Earth!
The swarming habit of the krill greatly assist the baleen whales which feed on them, Blue Whales preferring adolescent krill and Fin Whales favoring the adults. These swarms often extend over some hundreds of square meters; the maximum dimension recorded for a swarm is several kilometers. Krill can be dense enough to discolor sea water, and therefore at times can be easily spotted from the deck of a ship.
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In recent years, Antarctic krill has been the focus of much international attention and is already the object of commercial exploitation by many countries. Over-exploitation of such a living resource, upon which so much of the Antarctic marine ecosystem depends, could bring about a major ecological disaster. (See program 3 for comments on how krill support the entire Antarctic marine ecosystem.)
Websites
• Prehistory
More background information on the prehistory of Antarctica.
• Antarctic Adventure 1997
Information on the geography and climate of Antarctica.
