"Despite their vastness, we are having a major effect on the oceans and the marine ecosystems within them," said Ben Halpern of the National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara. "No single spot is untouched by humans."

Around 4% of the world's oceans showed a relatively low impact from man's activities. These regions were mainly around the poles, where the presence of seasonal or permanent ice limits human access, and off northern Australia. But large areas of the North Sea, the South and East China Seas, the Caribbean Sea, the eastern coast of North America, the Mediterranean Sea, the Red Sea, the Persian Gulf, the Bering Sea and several regions in the western Pacific were affected particularly badly.

"All types of human activity are affecting the oceans, not just climate change and fishing," said Halpern. "Our results show that when these and other individual impacts are summed up, the big picture looks much worse than I imagine most people expected. It was certainly a surprise to me."

Halpern and colleagues looked at the impact of 17 different human activities – including pollution, commercial shipping, species invasion, structures on the sea-bed, and climate-change factors such as ocean acidification, changes in sea surface temperature and increases in ultraviolet radiation. But they say that their study is likely to be an underestimate of the damage, as they were unable to include activities such as aquaculture, recreational fishing, illegal fishing and the presence of rubbish, for which no data was available.

The team examined the effects of the 17 activities on 20 different marine ecosystems – they included a rating of ecosystem vulnerability as some activities affect certain ecosystems more than others.

"There has been a lot of attention focused on damage to coral reefs and mangroves, but rocky reefs in shallow waters and continental shelves are damaged too," said Halpern. Seamounts and seagrass beds have also suffered while soft-bottom areas and open-ocean surface waters are the least impacted ecosystems.

Coastal areas can suffer from the effects of ten or more human activities, including agricultural run-off from the land. According to Halpern, the North Sea, English Channel and South China Sea "have an almost perfect storm of impacts", where the effects of commercial fishing, commercial shipping, land run-off and climate change combine to create a large effect.

The researchers hope that the map can act as a tool for the conservation and management of the oceans. It could highlight where to focus limited conservation resources, whether that's to improve areas that are already badly affected or to protect the remaining areas of marine wilderness.

"The problems can only be addressed globally," said Fiorenza Micheli of Stanford University, who would like to see integrated management of activity on the land and oceans and ocean zoning to restrict certain activities to some areas.

Halpern worked together with a team from the Hawai'i Institute of Marine Biology, Stanford University, Wildlife Conservation Society, University of North Carolina at Chapel Hill, US National Oceanic and Atmospheric Administration (NOAA), World Wildlife Fund, Environmental Defense, Ocean Conservancy, University of California, Santa Barbara, University of Maine, all in the US, and Nature Conservancy, UK, and Canada's University of British Columbia.

The researchers reported their work in Science and at the American Association for the Advancement of Science (AAAS) meeting in Boston, US.