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OZONE DAMAGING FISH DNA
By Sean Henahan, Access Excellence WASHINGTON, D.C. (4/21/97) Increased ultraviolet radiation attributed to the ozone hole over Antarctica is causing measurable changes in fish DNA, according to a new study supported by the National Science Foundation. Biologists from Northeastern University and the University of Texas uncovered the first direct evidence that increased ultraviolet light (UVB) damages the DNA of animals in the eggs and larvae of icefish, an Antarctic fish lacking hemoglobin. After collecting specimens in the Antarctic waters, the scientists demonstrated that icefish eggs accumulate significant levels of DNA lesions called cyclobutane pyrimidine dimers. "We were surprised at the extent of the DNA damage we found," said Kirk Malloy, biologist at Northeastern, "although we still need to know what happens during the rest of the year when the ozone hole closes up." The ozone hole opens up over Antarctica every southern spring, letting more UVB from the sun penetrate to the earth's surface. "Ozone depletion has previously been shown to harm one-celled marine plants in Antarctica. We've now documented significant damage at a higher level of the food chain," said William Detrich, a Northeastern biologist. "It is striking how closely the damage to the fish eggs tracked with the increased intensity of ultraviolet light." The studies were done on cruises in waters around the Antarctic Peninsula, the finger of land that juts up toward South America. The protective ozone layer over Antarctica has thinned over the past two decades, as human-created chemicals called chlorofluorocarbons have risen to the stratosphere and helped to destroy ozone. Antarctica's ozone levels typically drop to less than half of normal during the spring ozone hole, allowing wavelengths of sunlight harmful to life to penetrate to the earth's surface and into ocean waters. The ozone layer has also thinned, although less so, in temperate regions. Ozone depletion is predicted across even broader areas of the globe over the next century. The excess ultraviolet light may slow a fish's growth, hamper cellular processes such as transcription and mitosis, and divert precious energy to DNA repair. "Increased UVB may ultimately let fewer larvae survive to adulthood," Malloy said. The biologists also found that animals vary in how fast they can repair damage to their DNA. Organisms such as icefish and krill, which breed in spring and release their eggs into ocean waters at the peak of the ozone hole, can repair DNA more than twice as fast as rockcod and other fish that breed in winter. Detrich believes that animals that breed in spring and summer when the sun is out "are a little better prepared by nature to face the ozone hole." The researchers plan to explore whether the DNA damage actually does hamper the animals' ability to survive. In any case, key members of the Southern Ocean food web such as larval and adult fish, krill, copepods, and some zooplankton -- the food base for seabirds, whales, and seals -could all be vulnerable to increased UVB. The research appeared in the February 17, 1997 issue of the Proceedings of the National Academy of Sciences. Related information on the Internet
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