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Fishing, fertilizer runoff, pollution, shipping, climate change—these are just a few of the ways that human activities influence the oceans that cover 70 percent of Earth's surface. And in all that vastness—139 million square miles (360 million square kilometers)—less than 4 percent remains unaffected, and more than a third has suffered serious human impacts, according to a new map published in Science.
Marine ecologist Ben Halpern of the University of California, Santa Barbara's National Center for Ecological Analysis and Synthesis and an international team of colleagues first listed 17 ways humans affect the oceans and then mapped each of them. By overlaying each impact on top of one another, the ecologists created a "current state of affairs for the oceans," Halpern says. "I was really surprised that there is no single spot on the planet that isn't being affected by at least one of these factors."
The map offers a guide to the most impacted areas, not surprisingly located where the most human activities occur, such as in waters adjacent to cities on the coasts of the North Sea, Mediterranean, Persian Gulf and South China Sea as well as off North America's eastern seaboard, among others. Yet, the map is crude, Halpern says. "Aquaculture, recreational fishing, sediment input from rivers that are being blocked by dams, atmospheric pollution—we know these are problems or potential problems and we wanted to include them but we just couldn't find the data," he notes. "Our results are almost certainly conservative."
Coral reefs, among other ecosystems, are suffering mightily at the hands of humans. It remains unclear, though, whether the host of impacts they face will compound themselves or cancel each other out, says marine ecologist John Bruno of the University of North Carolina at Chapel Hill, who also contributed to the map.
Shallow seas with muck at the bottom and the deepest parts of the ocean proved the least affected so far, due to the resilience of those ecosystems or a lack of good knowledge. "The deep water is such a vast, relatively unexplored area, we just don't know what kinds of impacts we're having on those ecosystems," Halpern says. "We spend trillions of dollars going to the moon and we don't really know what's going on in our own oceans yet."
Although the Bering Sea is an area of strong human influence, the polar seas are among the few watery stretches that show little sign of humanity's impact—yet. As these areas continue to warm under climate change, however, dwindling sea ice may open up new areas to fishing and other forms of human activity, the researchers warn.
But there are reasons for hope. The Marine Conservation Alliance (MCA)—a fishing industry group based in Juneau, Alaska—has called for a ban on fishing north of the Bering Strait, according to MCA executive director David Benton. "Let's shut this puppy down until we understand the effects," he says. "We don't want to be part of the problem for polar bears" and other Arctic animals.
And the tiny Pacific nation of Kiribati—just 313 square miles (810 square kilometers) of atolls—has decided to protect more than 10 percent of its territorial waters—158,000 square miles (410,500 square kilometers), an area roughly the size of California—as the largest marine reserve in the world.
These kinds of efforts are exactly what the mapmakers hope to inspire. By revealing areas where mankind does its worst, the map also divulges where mankind can do best in limiting its impact. "It's definitely serving as a wake-up call to really start paying more attention to what we're doing to the oceans," Halpern says. "I hope people step up to the plate, knowing they have the opportunity to make a difference."