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Researchers who studied a string of Pacific Ocean atolls are painting the first detailed picture of pristine coral reefs and how they can be disrupted by people — particularly, they said, by fishing.

The researchers, from the Scripps Institution of Oceanography and elsewhere in the United States and abroad, surveyed every form of life last summer in the northern Line Islands, a chain south of Hawaii. Their survey encompassed everything from microbes to sharks and other big fish at the top of the food chain.

“Reefs without people” were healthier than populated reefs, they say in a report to be posted Wednesday in the online Public Library of Science Biology. The ecosystems at Kingman and Palmyra, the northernmost and least populated atolls, are dominated by large predators like sharks and groupers, and corals there are robust, they said, while Tabuaeran and Kiritimati to the south, the most populated atolls, are characterized by fleshy algae, small plankton-eating fish and degraded corals.

In a commentary also published online, Nancy Knowlton and Jeremy B.C. Jackson, coral experts at Scripps and the Smithsonian Institution, said the new work was notable because it produced data at sites “across a full spectrum of human impacts.” Without this kind of data, they write, studying coral reefs is like trying to discern the ecological structure of the Amazon rain forest by looking at the cattle ranches and soybean fields that have replaced much of it.

Actually, they write, it is even worse. Scientists can still visit vast areas of intact rain forest and have decades of data from earlier researchers. “The situation is very different for the oceans,” Knowlton and Jackson wrote, because degradation of ocean ecosystems is so pervasive, and underwater observation is relatively recent. As a result, they said, scientists disagree over the relative importance for coral of local factors like overfishing and pollution as against global problems like climate change and the acidification of oceans it causes.

The Line Islands work will not settle those arguments. But the scientists noted great differences in the fish communities at inhabited and uninhabited reefs, which they attributed to fishing pressure on shark, grouper, snapper and other large predators, said Enric Sala, an ecologist formerly at Scripps and now at the National Council for Scientific Research in Spain.