Map charts human toll on oceans

Posted: 15 February 2008

Human activity has left a mark on nearly every square kilometre of sea, severely compromising ecosystems in more than 40 per cent of the planet's waters, according to a groundbreaking new map of the state of the world's oceans.

The map, presented at the annual meeting of the American Association for the Advancement of Science and published in Science magazine, combines 17 man-caused 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.

An international team of 20 scientists in the US, Canada and UK worked to weigh and compare the stressors, overlaying them on top of maps that the scientists built of various ecosystems, with data obtained from shipping maps, satellite imagery, and scientific buoys. Then marine scientists modelled how different ecosystems would be affected by the stressors, mapping so-called impact scores onto square-kilometre-sized parcels worldwide. The scores correspond to colored pixels on the new map.

Human impacts on oceans map
Human impacts on oceans map
Red and orange areas indicate highly impacted areas of the ocean. © Science/ B S Halpern. Click on map to enlarge.
The 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.

"In the past, many studies have shown the impact of individual activities," said Dr Halpern. "But here for the first time we have produced a global map of all of these different activities layered on top of each other so that we can get this big picture of the overall impact that humans are having rather than just single impacts."

The data suggest, for example, that ecosystems found in rocky reefs and on 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.

Co-author Mark Spalding, of the international conservation group The Nature Conservancy, said: "I think the big surprise from all of this was seeing what the complete coverage of human impacts was. There's nowhere really that escaped. It's quite a shocking map to see."

"Out on the high seas, climate change and fishing were far and away the strongest influences," he added. "The least impacted areas are the polar regions but they are not untouched."

The UK Marine Conservation Society (MCS) points out that the North Sea off NE Scotland and the English Channel fall into the "very high impact" category. This reflects the considerable amount of oil and gas development in the former and shipping, fishing, climate and pollution around Britain.

"This report's new global map of human impacts reiterates the fact that UK seas are in a shocking state of degradation. Urgent action must be taken by Government to achieve a more effective balance between use and protection," said Melissa Moore, MCS Senior Policy Officer.