Despite the oceans' vast expanse across 70 percent of the Earth, their every reach is affected by human activities, a new study by researchers at the University of North Carolina at Chapel Hill and others says.

The study, published today in the journal Science, says that over 40 percent of the world's oceans are suffering from multiple human influences, including overfishing, pollution, climate change and commercial shipping traffic. And no part of the deep blue sea is entirely unaffected, the scientists found.

The team of scientists from the United States, Great Britain and Canada synthesized global data to see how 17 human functions threaten marine ecosystems such as coral reefs, sea grass beds and continental shelves.

"The big picture looks much worse than I imagine most people expected," said lead scientist Ben Halpern at the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara.

The mapping technique uses overlays similar to an online satellite map, which allows users to add layers of highways, schools and parks to find the most congested areas. For the scientist, the approach reveals ocean expanses where threats to marine ecosystems overlap.

The areas most affected, the study said, include the North Sea, South and East China seas, Caribbean, eastern seaboard of North America, Mediterranean, Red Sea, Persian Gulf, Bering Sea and several regions of the western Pacific.

The ecosystems most threatened are coral reefs, which house more than 25 percent of all marine life; sea grass beds that provide nurseries for young fish; and mangroves that grow in coastal habitats. Almost half of all coral reefs experience medium high to very high impact.

"There is still a perception that the oceans are the high seas and are so vast," said Elizabeth Selig, an author of the study and a doctoral student in UNC-CH's curriculum in ecology in the College of Arts and Sciences. "This is really the first time we've been able to get a picture of what human activities are affecting which places."

The least affected were areas near the poles where ice limits human access, but the study did not measure ice melt. The scientists said projections of polar ice loss suggest that the impact on these regions will increase substantially.

David Garrison, biological oceanography director at the National Science Foundation, which supported the study, said in a statement that the research is "a critically needed synthesis of the impact of human activity on ocean ecosystems." Previous studies have focused on single activities or isolated ecosystems.

A model for others

He said the effort is likely to be a model for assessing these effects on a regional and local scale.

The study quantifies the extent of the problems that marine scientists have long known to be issues, said John Bruno, associate professor of marine sciences at UNC-CH and co-author of the study.

"But it's not enough to just know something's a problem," Bruno said. "If you want to do something about it, you have to know where the problems are and what's causing them."

Bruno and Selig contributed information about rising ocean temperatures, which can damage the health of coral reefs. The readings were then used to quantify changes in ocean temperature and estimate the threat from global warming.

Bruno said the new map reveals for the first time the geographic extent and precise locations of ocean warming.

"It isn't really warming up like a pot of water on a stove," Bruno said.

Instead, scientists see patches of the ocean with spikes in temperatures of a few degrees. But such temperature anomalies can cause coral disease outbreaks, previous studies by Bruno and Selig have said.

With the information, the research team can now begin to tackle the bigger problem of understanding and forecasting how ocean warming will affect marine ecosystems, he said.

Sean McKeon, president of the N.C. Fisheries Association, which represents commercial fishermen, dealers and processors, took issue with the study, saying most of the world's oceans were not affected at all by humans.

"The oceans are so vast and deep and inaccessible to most vessels," McKeon said. "We fish in relatively small areas of the ocean."

What is acceptable?

McKeon said the question should be what levels of impacts were acceptable to provide seafood and other products from the ocean.

"We impact the land when we raise crops," McKeon said. "I don't know anybody who would argue we get rid of farms. We impact forests when we use forest products."

Sera Harold, Southeast regional representative for the Marine Fish Conservation Network, which advocates healthy fisheries, said it was significant that the east coast of North America was one of the most threatened areas.

"We're in a lot of denial," Harold said. "We don't think about pollution and how it affects the ocean. Each of us pours fertilizer on our lawn or doesn't tune their car and doesn't realize the impact we're having. Every once in a while, it's nice to have somebody remind us we need to take better care of the ocean."