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An Icy World Full of Life
WHAT was once considered a cold and hostile desert has been revealed as being in reality the environment for a multitude of ingeniously adapted species, which arc of vital importance for the food chains of the polar seas. It is only in recent years that researchers have been able to come to grips with this fascinating ecology, which had htthcrlo remained more or less concealed in the fine clefts and hollows of the ice of the polar seas Scientists from the Federal Republic of Germany are playing a significant role tn the study of this ecology.
Ice covers more than seven million square kilometres of the North Polar Sea; by the end of the Northern winter, this figure can even approach 14 million — enough lo cover the entire area of the Federal Republic almost 40 limes over.
In the South Polar Sea, around the continent of Antarctica with its over 14 million square kilometres, the area covered by ice is subject to even greater changes. There, life occupies the numerous cracks, small channels and hollows of this icy armour. At Alfred-Wegener Institute for Polar and Marine Research in Bremerhaven, an interdisciplinary working group has for many years been researching the Antarctic environment in particular.
According to biologists Dr. Michael Spindler and Dr. Gerhard Dieckmann of the Institute, reporting In the well-known scientific journal Spcktrum dcr Wissenschaft (2/91) and elsewhere, the va riety of species ranges from bacteria and algae lo Invertebrate animals. In the polar regions, the greatest in number are the diatomae.
In some places they arc so numerous that the bottom side of the ice is dark brown, and the interior contains brown
streaks Although the German explorer and biologist Christian Gottfried Ehrenberg (1795 1876) first drew attention to such organisms in the Ice precisely 150 years ago, until the beginning of the nineteen-sixties they were regarded as more of a curiosity With the German icebreaking research ship Polar-stern, which was commissioned In 1984. scientists from the Alfred Wegener Institute were able to investigate marine lee as an environment for the first lime.
Around 300 species of dl atomac have been found in the Arctic to date. Several hundred million of these stngfe-cell organism* may be counted tn a single litre of melted ice, of which the rod shaped variety is the most frequent. Further common organisms are the flagellate algae, or also the armoured or dinoflagellates. They too may be found In the millions in a litre of marine ice, while other algae groups, such as yellow-green or green algae, occur with much less frequency or species variety. Bacteria arc also plentiful but their distribution, as that of fungi, has not yet been studied In detail.
These hosts of organisms are in turn an Important food source for other single-cell creatures such as flagellates, clliates and foraminiferans.
More highly organised multicell .organisms, such as flatworms, rotifers, nematodes, chaetopods, copepods, am phlpods and slugs several mil limetres in size, also live In this icy undersea world However, the environment of ice makes hard demands on its inhabitants, they must not only "he able to stand relatively high salt contents and low temperatures, but also. In the case of green plants, be able to make do with an extremely low ration of light
While the marine ice grad-
ually "freshens out", the sail content in the cracks Increases as the temperature drops. Scientists have measured concentrations of 70 per thousand at minus four degrees Celsius, and as high as 145 per thousand at minus ten degrees. At the same lime, laboratory experiments have shown that diatomaa, for example, can still multiply at mi nus 5.5 degrees and salt contents up to 95 per thousand, and can survive for longer periods under even harder con-
dltions.
Certain diatomae are protected against frteezing within the cell by
"antifreeze", such as the amino acid proline: in other organisms. Inorganic ions or glycerine prevent such life-threatening freezing. A further survival problem for the flora in particular Is the lack of light under the pack ice. which the algae seem the master without any apparent difficulty. They achieve their highest photosynthesis performance with
just a fraction of the light In- ' tensity which is measurable on the surface of the earth.
The researchers found the greatest algae concentrations In the lower range of the Antarctic Ice ecology. "In summer, the chlorophyll value* there reach a level of more than 2,000 milligrams per cubic metre," they report. In the more productive North Sea, the comparison values are just 20 to 50 milligrams, even during the spring algae blooms.
— GRS