Human activities are affecting every square mile of the world's oceans, according to a study by a team of American, British and Canadian researchers who mapped the severity of the effects from pole to pole. The analysis of 17 global data sets, led by Benjamin S. Halpern of the National Center for Ecological Analysis and Synthesis in Santa Barbara, Calif., illustrates the extent to which humans are reshaping the seas through overfishing, air pollution and commercial shipping. The study, published in the journal Science, examines the impacts on nearly two dozen marine ecosystems, including coral reefs and continental shelves. "For the first time we can see where some of the most threatened marine ecosystems are and what might be degrading them,' said Elizabeth Selig, a Ph.D. candidate at the University of North Carolina at Chapel Hill and a co-author, in a statement. "This information enables us to tailor strategies and set priorities for ecosystem management. And it shows that while local efforts are important, we also need to be thinking about global solutions.' The team of scientists analysed factors, including warming ocean temperatures due to greenhouse gas emissions, nutrient runoff and fishing. They found that the areas under the most stress included are "the North and Norwegian seas, South and East China seas, Eastern Caribbean, North American eastern seaboard, Mediterranean, Persian Gulf, Bering Sea, and the waters around Sri Lanka.' Some marine ecosystems are under acute pressure, the scientists concluded, including sea mounts, mangrove swamps, seagrass and coral reefs. Almost half of all coral reefs, they wrote, "experience medium high to very high impact' from humans. Overall, rising ocean temperatures represent the biggest threat to marine ecosystems.