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February 14, 2008

Ocean Map Charts Path of Human Destruction

Image courtesy of B.S HalpernFour years in the making, a groundbreaking new map of the state of the world's oceans was released today, and its message is stark: Human activity has left a mark on nearly every square kilometer of sea, severely compromising ecosystems in more than 40 percent of waters.

The map, presented here at the annual meeting of the American Association for the Advancement of Science--and published tomorrow in Science--combines 17 anthropogenic stressors, including coastal runoff and pollution, warming water temperature due to human-induced climate change, oil rigs that damage the sea floor, and five different kinds of fishing. Hundreds of experts worked to weigh and compare the stressors, overlaying them on top of maps the scientists built of various ecosystems, with data obtained from shipping maps, satellite imagery, and scientific buoys. Then marine scientists modeled how different ecosystems would be affected by the stressors, mapping so-called impact scores onto square-kilometer-sized parcels worldwide. The scores correspond to colored pixels on the new map.

Researchers don't know what the impact scores, which mostly ranged from 0 to 20, mean in terms of specific damage for different ecosystems. And without hard data sets, marine ecologists must rely on fuzzy terms like "degraded" or "severe." But previous studies of devastated coral reefs provide some context. A 2003 paper in Science showed that certain coral reef ecosystems in the Caribbean Sea and off Australia had lost as much as half of their species since pre-industrial times. This level of damage corresponds to an impact score of 13 or 14 in the current map, values found in wide swaths of orange on the map of the world's oceans.

Those figures are sobering, says marine ecologist Benjamin Halpern of the National Center for Ecological Analysis and Synthesis in Santa Barbara, California, who led the effort. The data suggest, for example, that ecosystems found in rocky reefs and continental shelves "are being impacted even more" than coastal coral reefs which get much more attention. But coral reefs are in bad shape themselves: The map indicates that nearly half of global reefs are experiencing serious, multiple impacts, including damage from fishing and ocean acidification.

"The takeaway message of the paper is that one needs to take into account the cumulative effects of different threats to the ocean," says Duke marine ecologist Larry Crowder, who wasn't part of the effort. Still, while the map is a "bold attempt," Crowder notes that it is far from comprehensive. Some very severely threatened ecosystems, like certain rare reefs, are too small to show up on the map, he notes, and other data, such as the cumulative impact of fishing historically, are simply not available. Scientists in the broader community will be able to update the various datasets that form the map, which could fill some of these gaps.

--Eli Kintisch

Check out the homepage of the new map