Published on February 15, 2008

Scientists Reveal First-Ever Global Map of Total Human Effect on Oceans

More than 40 percent of the world's oceans are heavily affected by human activities, and few if any areas remain untouched, according to the first global-scale study of human influence on marine ecosystems.

By overlaying maps of 17 different activities such as fishing, climate change and pollution, the researchers have produced a composite map of the toll that humans have exacted on the seas.

The work was conducted at the National Science Foundation (NSF)'s National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California at Santa Barbara, and involved 19 scientists from a range of universities, NGOs, and government agencies.

The study synthesized global data on human impacts to marine ecosystems such as coral reefs, seagrass beds, continental shelves and the deep ocean.

Past studies have focused largely on single activities or single ecosystems in isolation, and rarely at the global scale. In this study the scientists were able to look at the summed influence of human activities across the entire ocean.

The study reports that the most heavily affected waters in the world include large areas of the North Sea, the South and East China Seas, the Caribbean Sea, the east coast of North America, the Mediterranean Sea, the Red Sea, the Persian Gulf, the Bering Sea and several regions in the western Pacific. The least affected areas are largely near the poles.

Human influence on the ocean varies dramatically across various ecosystems. The most heavily affected areas include coral reefs, seagrass beds, mangroves, rocky reefs and shelves and seamounts. The least impacted ecosystems are soft-bottom areas and open-ocean surface waters.

The research involved a four-step process. First, the scientists developed techniques to quantify and compare how different human activities affect each marine ecosystem.
For example, fertilizer runoff has been shown to have a large effect on coral reefs but a much smaller one on kelp forests.

Second, the researchers gathered and processed global data on the distributions of marine ecosystems and human influences.

Then the scientists combined data from the first and second steps to determine "human impact scores" for each location in the world.

Finally, using global estimates of the condition of marine ecosystems from previous studies, the researchers were able to ground-truth their impact scores.

Despite all this effort, the authors acknowledge that their maps are still incomplete, because many human activities are poorly studied or lack good data.

This study provides critical information for evaluating where certain activities can continue with little effect on the oceans, and where other activities might need to be stopped or moved to less sensitive areas.

As management and conservation of the oceans turns toward marine protected areas (MPAs), ecosystem-based management (EBM) and ocean zoning to manage human influence, such information will prove invaluable to managers and policymakers.

"Conservation and management groups have to decide where, when, and what to spend their resources on," said Kimberly Selkoe, a scientist at the University of Hawaii. "Whether one is interested in protecting ocean wilderness, assessing which human activities have the greatest impact, or prioritizing which ecosystem types need management intervention, our results provide a strong framework for doing so."