Enric Sala remembers the exact moment he decided he wanted to be a National Geographic explorer — one of the few lucky souls who launch expeditions financed and documented by one of the nation’s most venerable institutions. A decade ago he was sitting in his office at the Scripps Institution of Oceanography in La Jolla, Calif. — an academic perch with an idyllic view of the Pacific Ocean — as he unwrapped the brown paper that used to cover issues of National Geographic.

“There’s a guy walking in the African jungle looking like a maniac, with a bunch of pygmies behind him, exhausted,” Sala recalled. “I said, ‘Wow, this is what I want to do.’ ”

It was National Geographic explorer Mike Fay, who had walked more than 2,000 miles across the Congo Basin. The series about his journey inspired the president of Gabon to create his country’s first system of national parks.

The 42-year-old Sala — a Spaniard and respected marine biologist — gave up a tenured post at Scripps three years ago to move to the District, “trying to save the last wild places in the ocean” as National Geographic’s newest explorer-in-residence.

Being a 21st-century explorer, it turns out, entails advocacy as well as adventure. And it reflects a different mission for National Geographic, a 123-year-old Washington institution that no longer simply showcases stunning photographs and stories of the planet’s most remote places, but now acts on their behalf.

National Geographic has funded nearly 10,000 expeditions over the past century and reported on them in its magazine’s pages, bringing extraordinary sites to a global audience. It helped Robert E. Peary explore the North Pole in 1909 and assisted Hiram Bingham as he excavated the lost Inca city of Machu Picchu between 1912 and 1915. Its money helped produce iconic images of the underwater world — as Jacques Cousteau conducted oceanographic research in the 1950s and ’60s — and reshape the way we view evolution, as Mary and Richard Leakey unearthed the fossils of some of the earliest humans.

Recently the institution’s 14 explorers have started posing some uncomfortable questions to their longtime benefactor. They are nudging it to engage in public policy debates, though they don’t dispatch staffers to Capitol Hill as other environmental groups do.

“Increasingly now what they tell us is things are changing — the historical, cultural, natural resources of this planet are changing, and, in many cases, they’re disappearing,” said Terry Garcia, National Geographic’s executive vice president for mission programs, adding that the explorers have started to ask, “Do you really want us to simply chronicle the demise of the planet?”

Brian Skerry, who has worked as a National Geographic contract photographer for 13 years, underwent this transformation over the course of his career.

“At first, when I began, I was only interested in the celebratory picture,” he said during a panel on oceans at the Center for American Progress this month. After discovering “environmental stories I couldn’t ignore,” Skerry said, he began reporting such subjects as industrial fishing and climate change. “It’s not like a grocery store, the ocean; we can’t keep taking things out and expect everything’s okay.”

The explorers use both high- and low-tech equipment, some of which is financed by National Geographic, to conduct their high-stakes journeys. Fay made his entire Congo trek in a pair of shorts and Tevas, but he now uses everything from kayaks to snowshoes for his explorations. Robert Ballard relies on remotely operated vehicles at times to investigate shipwrecks in the Black Sea. Documentary filmmakers Dereck and Beverly Joubert spot African wildlife — and those who hunt the animals — from small aircraft. And Sala uses deep-water “drop cams,” mini-helicopters and high-definition underwater cameras.

Sala made the leap to National Geographic full time in 2008, identifying potential marine reserve areas as an ocean fellow at the group’s headquarters. Garcia recalled how Sala sat in his D.C. office and explained the limits of his academic job, saying that it offered security and intellectual freedom, “but what it means is I’ll just be writing one academic paper after another, and all the while the ocean, and the marine organisms in the ocean, are going to be disappearing. And I don’t want to do that.”

Sala did not become an explorer-in-residence overnight. He was awarded the title “emerging explorer” in 2007 before ascending in National Geographic’s hierarchy and becoming an ocean fellow. This caused some confusion when in June he called his parents in Girona, Spain, to deliver the news that he had been named an explorer-in-residence, along with filmmaker James Cameron.

“They both said, ‘I thought you were already an explorer,’ ” he recounted.

Sala — who is striking and lean, with brown hair he pulls back in a ponytail — leads what he calls “a schizophrenic life,” interspersing expeditions with policy and academic work. Just a few weeks before Sebastián Piñera was elected president of Chile in January 2010, Sala met him at the World Economic Forum and chatted about how both of them had been scuba diving off Chile’s Sala y Gomez, an area near Easter Island.

As a couple of other Latin American presidents pulled Piñera away, Sala said, “So when you become president, we’re going to talk about this place.” Sala lobbied him with a letter and through several intermediaries; less than a year after taking office, Piñera declared the 58,000-square-mile area a marine reserve, off-limits to extractive activities.

Though he was raised speaking Catalan (he reverts to his first language when cursing or taking personal notes), Sala spoke to Piñera in Spanish. He also speaks French, Italian and English fluently, a lingual dexterity that adds to his persuasiveness.

“I call him the Antonio Banderas of the marine world, because he’s so charming,” said Nancy Baron, science outreach director for the group COMPASS, which helps researchers engage in public policy.

This includes appealing to allies such as the pop singer Bjork, who decided to donate $34,000 from “Mount Wittenberg Orca,” a recording she did with the experimental rock band Dirty Projectors, to fund Sala’s marine reserve work.

“He seemed to be a man on a mission who would not mess about,” the Icelandic singer said in a phone interview, adding that after meeting him at National Geographic’s headquarters, she became convinced that if he planned a project, “it would actually work; it would not be just talk.”

In fact, Sala spends much of his time planning expeditions that cost between $500,000 and $1 million. They include not only researchers but photographers and bloggers, who can chronicle the wonders of areas he lobbies to place off-limits.

Ken Weiss, the Pulitzer Prize-winning Los Angeles Times reporter who journeyed with Sala to the South Pacific island of Palmyra in 2005 when Sala was based at Scripps, describes him as the “most stylish diver I’ve ever seen.” He is meticulous about his Italian diving gear, with elongated fins and the sort of soft and malleable neoprene fabric that Mediterranean spear fishermen prefer for spending an extended time underwater.

“He’s just suspended in the water column,” Weiss recalled, adding that as Sala remained motionless horizontally, he resembled “a matador, with sharks swimming all around him.”

Much of marine biology — counting fish in transects, sorting the numbers afterward — can be tedious, and Sala has little patience for it.

Boris Worm, marine biologist at Dalhousie University in Nova Scotia, recalled how he and Sala spearheaded a groundbreaking workshop a few years ago that produced the headline-grabbing conclusion that the world’s commercial fish stocks could collapse by 2048: “I was the guy trying to whip people into crunching data; he was going out with people and drinking wine and beer, and having these discussions that led to inspired ideas. So it was a good tag team.”

Sala still publishes academic papers regularly. Last week he was co-author of a study in the Public Library of Science ONE journal showing that Cabo Pulmo National Park, in an area that Sala’s childhood hero Cous­teau called “the aquarium of the world,” is the world’s most robust marine reserve.

What Sala relishes, however, is immersing himself in places such as the waters around Costa Rica’s Cocos Island, where 200 hammerhead sharks can swim by as he’s holding his breath, or off Kiribati’s Millennium Atoll, where giant clams in electric blue and fluorescent green carpet the seafloor.

“Because they filter water, it is so clear you feel you are flying,” he said. “The entire experience is hallucinogenic because you feel you are flying on this carpet of giant clams.”

When he was done diving, he made a pitch to the Kiribati government that it should protect Millennium from exploitation. He showed officials pictures of what was underwater. “You should have seen their faces,” he said. “They had no idea what they had there.”

A few obstacles remain — Sala is working on drafting an economic model to show developing nations such as Kiribati that they can profit more from protecting the sea than mining its re­sources. “I am a salesman of ideas,” he said.

And National Geographic has limited resources itself, making financing future expeditions “a challenge,” as Garcia put it. But he has no doubt that Sala will be back at sea soon. “If we’re not exploring, if we’re not sending people into the field, then what are we?”