Researchers have found the first evidence that marine plants in the ocean around Antarctica, the tiny organisms upon which a vast ecosystem depends, are damaged by the ultraviolet light that pours through the seasonal hole in the ozone layer.

Scientists caution that the work is preliminary and may not accurately reflect what is happening in Antarctic waters. But laboratory tests at Palmer Station in Antarctica show that ultraviolet (UV) radiation can alter the genes of common species of Antarctic phytoplankton, the one-celled marine plants that sustain a food web that includes krill, fish, penguins and whales.

The findings were announced yesterday by the National Science Foundation, which pays for the work. The research will be published in the Antarctic Journal and in Marine Biology.

The scientists found that different species of phytoplankton respond differently to the same dose of ultraviolet. The UV light caused mutations in the plants' DNA, some of which were lethal. Some species suffered much DNA damage, while others escaped with little.

"We found a very large range in abilities of these organisms to survive UV. Some species were very resistant and were still able to divide and reproduce. In others, a small amount of UV produced a drastic reduction in their ability to divide," said Deneb Karentz of the University of California at San Francisco, who did the studies with colleague David Mitchell. "Essentially we observed a wide range of responses. It's possible the same thing would be happening in the field."

Karentz said such variations in response mean it is possible that some species would proliferate, while others might die back. A change in species composition of phytoplankton would have unknown effects on the Antarctic ecoystem, though Karentz and other scientists said it is possible it could disturb the food web.

While the UV doses delivered in the lab were greater at any one moment than those experienced in Antarctic waters, the studies are thought to reflect the relative sensitivity of the marine plants.

"One of the big questions is what the ultraviolet will do to species composition," said Greg Mitchell of the Scripps Institution of Oceanography in San Diego. "At the present time, I don't know if anyone could say what a change in species mix would do."

In Antarctica, especially during the annual algae blooms, the most common marine plants are diatoms, which have glasslike shells made of silica. These and other plants are eaten by krill and other small animals called copepods, which graze on the floating marine plants like sheep on grass.

Research by Robin Ross and Langdon Quetin of the University of California at Santa Barbara suggests that krill may be more likely to catch and eat the larger plants than smaller ones. "It looks like most of their selection is based on size," Ross said.

Ross said if the larger plants are depleted by UV damage, the krill may go hungry.

Scientists say they have not yet detected any change in the Antarctic ecosytem that they can attribute to the annual appearance of the ozone hole, which is caused by pollution of the atmosphere with chlorofluorocarbons, or CFCs, which are used as aerosol propellents, refrigerants and plastic foaming agents.

Natural fluctuations from year to year make it difficult to see what effect, if any, the increased ultraviolet has had since the ozone hole was discovered a decade ago. A large expedition funded by the National Science Foundation to study the effects of ozone hole on Antarctic marine life is is set for this fall.