Not a square kilometer of the world's oceans has been left untouched by human activities, a new study shows.
Ocean ecosystems face a wide range of threats from human sources, including overfishing, pollution, and rising ocean temperatures and ocean acidification caused by global warming.
An international team of scientists gathered global data for 17 different types of these human impacts and fed them into a model that produced a map of the world's oceans with each square kilometer assigned a value of the level of impact at that particular spot. Their results are detailed in the Feb. 15 issue of the journal Science, and were presented today at the annual meeting of the American Association for the Advancement of Science in Boston.
The map showed that human activities have to some degree affected all parts of the oceans, with 41 percent being strongly impacted by several human-caused drivers.
"What is new today is that... we know how much of the oceans are in trouble and this figure is frighteningly high," said co-author Fiorenza Micheli, a Stanford University marine ecologist, at a news conference in Boston.
The most highly affected region of the world's oceans include the eastern Caribbean, the North Sea, the eastern North American seaboard, the Mediterranean, and the waters around Japan. Ecosystems at high risk included coral reefs, continental shelves, seagrass beds and mangroves.
"For the first time we can see where some of the most threatened marine ecosystems are and what might be degrading them," said study co-author Elizabeth Selig of the University of North Carolina.
Selig and her UNC colleague John Bruno contributed global ocean temperature data for the model that was more precise than previous data. The study showed rising ocean temperatures to be the most pervasive threat to marine ecosystems, with almost half of the world's coral reefs having recently experienced medium- to high-level impacts.
The study found that only about 4 percent of the oceans were relatively pristine and these were mostly in the polar regions. However, the authors caution that the model likely underestimates the impacts at the poles because they did not account for projections of future polar ice loss.
The map also shows that while some impacts, such as rising temperatures, are pervasive around the world, others, such as pollution from runoff are confined mostly to coastal areas. The authors say this knowledge will help to tailor conservation efforts to the impacts most important to particular ecosystems.
For example, in 2004, Australia completed a rezoning of the Great Barrier Reef marine park, an ocean area nearly the size of California, Micheli said. The vast array of ecosystems and users in this area called for a plan with three levels of conservation, and shows that complex conservation plans can be implemented, Micheli added.
"This information enables us to tailor strategies and set priorities for ecosystem management," said Selig. "And it shows that while local efforts are important, we also need to be thinking about global solutions."
Robin Lloyd contributed to this report from Boston.
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