Low-oxygen zones where sea life is threatened or cannot survive are growing as the oceans are heated by global warming, a new study warns. Oxygen-depleted zones in the central and eastern equatorial Atlantic and equatorial Pacific oceans appear to have expanded over the last 50 years, researchers report in Friday's edition of the journal Science. Low-oxygen zones in the Gulf of Mexico and other areas also have been studied in recent years, raising concerns about the threat to sea life. Continued expansion of these zones could have dramatic consequences for both sea life and coastal economies, said the team led by Lothar Stramma of the University of Kiel in Germany. The finding was not surprising, Stramma said, because computer climate models had predicted a decline in dissolved oxygen in the oceans under warmer conditions. Warmer water simply cannot absorb as much oxygen as colder water, explained co-author Gregory C. Johnson of the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory in Seattle. There are complex biological and chemical interactions in these low-oxygen regions, Stramma commented, adding that this needs to be more closely studied. Steven J. Bograd, a research oceanographer at the National Oceanic and Atmospheric Administration's Environmental Research Division in Pacific Grove, Calif., called the finding "compelling" but not surprising. Bograd, who was not part of Stramma's team, has studied trends in dissolved oxygen in the ocean off California, finding an expansion of the area of the continental shelf there that is exposed to low-oxygen conditions. "So, why should we care?" Bograd said. "Most marine species have minimum oxygen thresholds that they need for survival. As oxygen decreases, these animals will suffer and/or be compelled to move to other areas. Over time, the optimal area for various species will be compressed," he explained. Bograd's findings are reported in a paper scheduled for publication in Geophysical Research Letters. "We are not able to say definitively what has caused the oxygen declines off California. But we do know that waters from the eastern tropical Pacific"