For a bird's-eye view of human impacts on the Earth, scientists can study satellite images showing the continents in mottled colors that correspond to vegetation, desertification or human habitation. But those photos cannot tell them much about the big blue mystery, oceans, and how human activities affect them.
Now, a team of researchers, including a Stanford University scientist, has constructed the first global map of human influences on marine ecosystems by gathering and interpreting massive amounts of data from the professional literature and from researchers around the world. This study suggests that about 41 percent of oceans bear a serious human "footprint " and that few blue spots on our planet are likely pristine.
"A series of papers have highlighted the role humans are having on the degradation of the oceans, through specific activities," said Fiorenza Micheli, an associate professor of biology at Stanford. "It's timely to put it all together-to show how all the different effects sum up."
Micheli said maps of human influence should "guide ocean zoning and management of coastal waters." Scientists increasingly advocate zoning oceans to protect the hidden ecosystems below the surface. "By seeing where different activities occur and whether they occur in sensitive ecosystems, we can design management strategies aimed at shifting activities away from the most sensitive areas," Micheli said.
The researchers compiled data on 17 different human impacts to oceans, including fishing, coastal development, fertilizer runoff and pollution from shipping traffic. Previous studies have worked on a smaller scale, or have focused on only one ecosystem or human activity, examining a single piece of the global puzzle. To make the picture complete, Micheli and her colleagues built a global map detailing how these numerous human impacts would add up and affect 20 types of ecosystems.
"For some human activities, we have global data, like commercial fisheries catches," Micheli said. "For others, we developed models to estimate global impacts." The team consulted marine scientists and dug into years of literature describing human effects on different ecosystems, such as coral reefs, rocky reefs and deep, open waters. They developed a system to quantify how powerful each human influence is, and how fragile each ecosystem is. To map the damage, Micheli and her colleagues divided the ocean into 1-square-kilometer "cells." They determined the impact to each cell by what human activities have touched it, how forceful that touch has been and which ecosystems are there.
Their results suggest that coral reefs are in trouble; nearly half have taken a hard human punch. Other spots of concern include seagrass beds, mangrove forests in estuaries, seamounts, rocky reefs and continental shelves. Soft-bottom shallow and deep ecosystems, as well as the open ocean, fared best, though even they were not pristine in a majority of locations.
The study also shows that human influence runs deepest in the North Sea, the South and East China Seas, the Caribbean Sea, the Mediterranean Sea, the Red Sea, the Persian Gulf, the Bering Sea, along the Eastern Coast of North America and in much of the western Pacific. The oceans around the Artic and Antarctic poles have been affected very little, but the dwindling polar ice sheets will leave them vulnerable in the future, research suggests. Very limited impacts are also seen around northern Australia, in areas across the western-central Pacific and in small areas scattered along the coasts of South America and Africa. These estimates of human impact are probably optimistic, Micheli said. The study did not account for historical impacts to the oceans whose traces might still linger, and it did not include all possible impacts to marine ecosystems, only the 17 for which data were available or could be modeled.
The least affected areas are largely near the poles. "Unfortunately, as polar ice sheets disappear with warming global climate and human activities spread into these areas, there is a great risk of rapid degradation of these relatively pristine ecosystems," said Carrie Kappel, a principal investigator on the project and a post-doctoral researcher at NCEAS.
Importantly, 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 worldwide impact map is a scaffold, which should be filled in with on-the-ground research, Micheli said. "Globally, it's important to see what the most impacted areas are and where are the last wildernesses," she said. "Our results and approach, augmented with additional local information, can also inform management at a local and regional scale. Looking at the data globally, some information is lost."
Micheli and her colleagues already are fleshing out one corner of their modeled world by gathering empirical data for marine ecosystems of the California Current region; the current flows south from Alaska along the coasts of Washington, Oregon, California and Baja California. When that project is complete, they will present their findings to environmental agencies, including the administrations of the marine sanctuaries off the western U.S. coast.
Micheli also will present a talk titled "Trophic Responses in Marine Reserves: Lessons from Temperate and Tropical Ecosystems" on Feb. 16, in a symposium at the AAAS meeting. Focusing on how marine food webs recover in marine reserves, she will present examples of studies from tropical and temperate reef ecosystems. Of 920 species surveyed in 31 reserves, about 60 percent benefited from the reserves, Micheli said. She said these reserves have "an effect, not on just individual species but also on the structure of the whole food web, with greater abundances of top predators in reserves than unprotected areas." Marine reserves were first implemented in the 1960s, but Micheli said many have been established in the past decade, and studies are now answering long-standing questions about how well they work.
Micheli, one of the principal investigators, is scheduled to discuss the project during a press briefing scheduled for 1 p.m. Thursday, Feb. 14, at the American Association for the Advancement of Science (AAAS) annual meeting in Boston. She also will discuss the work, which is described in a paper in the Feb. 15 issue of Science, during a seminar at 8:45 a.m. Friday, Feb. 15.
The other principal investigators on the project are Benjamin Halpern of the National Center for Ecological Analysis and Synthesis (NCEAS) at the University of California-Santa Barbara, Kimberly Selkoe of NCEAS and the Hawaii Institute of Marine Biology, and Carrie Kappel of NCEAS.
Funding was provided by NCEAS, the National Science Foundation and a grant from the David and Lucile Packard Foundation to NCEAS.
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