Earthquakes, floodings and even meteors are nothing compared to the biological destructive forces of icebergs. When these colossi, weighing up to 2 million tons, collide with the bottom of the ocean, they crush bottom and sea life to powder. "All that remains is an almost sterile biotope" adds dr. Sandra Vanhove.
The biologist from the Marine Biology Department of Gent University in Belgium researches, with colleagues from Germany and the British organization Antarctic Survey, animal life on Antarctica. Since 1989 the researchers are bivouacking on a regular basis on Signy Island in the Wedell Sea near the Antarctic continent.
As soon as an iceberg has passed the island, the researchers dive into the ice cold water to look for what remains of the sea-bottom and the fauna. On the water surface the calved icebergs may seem not dangerous, but the major part hidden under the surface causes a real destruction to life at the sea bottom. Strong currents and tides make the iceberg fall apart and bump over the bottom, causing destruction to anything on his way. If the movement of the water is less strong, then the bottom of the iceberg scours the sea-bottom with the same result. According to the size of the iceberg, a groove up to 130 meters wide and 5 meters deep, betrays the route, .
The researchers paid special attention to one iceberg that passed the island. It stuck to the sea-bottom on a depth of 9 meters. The berg stayed on this sole place for 30 hours and then it resumed bobbing its journey.
After research it became clear that especially the fauna bigger than 1 millimeter had suffered from the scouring and bobbing iceberg. The snails, testaceans, lobsterlikes and worms were crushed. Six out of eight species turned to be exterminated. Only 0.5 % of the remaining species survived the collision with the iceberg.
Also many animals bigger than one millimeter suffered. Ninety percent of this so called meiofauna did not survive the passing of the iceberg. The number of little eels in test-glasses with a diameter of 5 centimeters (2 inches) were diminished from more than one million to less than 10 000 specimens.. The sand corns between which the meiofauna usually lives, were taken away by the iceberg and pressed together to a compacted mass.
Nature though has a meaning with this rough treatment. "It gives animals a new chance to start anew', Vanhove says. "And this benefits the diversity of species. In this way it is comparable to wood fires which strip the woods of all the old trees and give younger ones a chance.
The diversity of species that arises after a collision depends, according to Vanhove, on the size and duration of the iceberg disturbance. A collision between an iceberg and the sea-bottom does not always lead to a positive result. If one has to do with a giant iceberg the diversity of the sea-bottom life can be diminished very strong and in that situation some opportunist species will predominate. "In those places it will take 10 to 100 years until the ecosystem is restored." It is better if a smaller iceberg visits a place once in ten years, so that the bottom-life gets a chance to recover.
After the iceberg collisions they researched, the small animals returned quickly. On their own or led by whirling currents the small animals recolonized the destructed area in a few weeks. The recovery of the macrofauna (animals bigger than one millimeter) took more than hundred days. These animals are more "home bound" than the smaller animals and they return with the coming of new specimens only.
Sea-bottom disturbances by icebergs happen often. Although icebergs stay in 20 % of the oceans, sea life suffers predominantly around the Poles. The biggest icebergs pulverize bottom and sea-life up to 500 meters deep.
Now the researchers have determined the size of the destructions, they want want to know which animals specifically fall victim to the icebergs.
(Based on an article by Robert Stiphout in "de Volkskrant" May 1st 1999)
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