The next ten years will be the most important in the next 10,000, says Sylvia Earle, speaking to a spellbound audience on the luxury live-aboard dive boat the Seven Seas, which lies at anchor in the remote Indonesian archipelago of Raja Ampat. Here, hundreds of miles from the nearest town, the night is primordially dark, utterly silent except for the breathy, gently maternal voice of the prophetess, and when she evokes the astronauts, their epiphanies from space—how it is the sea, the sea that is life itself!—it almost feels as if the Seven Seas has lifted off and is flying among a billion stars. The wine helps, too.

Dr. Earle, who began diving in suits that are now in museums and who first achieved fame in 1970 with NASA's Tektite II all-women mission, which spent two weeks living beneath the Caribbean Sea, has had the ears of presidents and World Bank officials. At 72, she's still exploring, still diving—still beautiful, too—and still shouldering the burden of a Cassandra who knows that the oceans are everywhere dying.

"We've gone from eating 'the big, the slow, and the tasty,' in E.O. Wilson's words, to consuming everything else, too," she says. "Krill paste is catching on in Europe. Krill paste! We're eating it all!" Dr. Earle has shown us a short film about fishing debris, with teams of volunteers hauling up a huge amount of shredded nets and monofilament longlines, a madman's ball of twine. But it's not the starving masses predicted by Malthus who are depleting the sea. The deadliest offender is the luxury seafood market—we of the gourmandizing West. "But it's all bushmeat!" Sylvia says, eyes flashing. "We do nothing to cultivate it; we just extract it as if the supply had no end." Worse still, the assault with trawler and fork is only part of the problem. What with pollution and global warming and coral bleaching, marine habitats are tipping domino style. The Great Barrier Reef is a shadow of itself, the Galápagos fading fast. "We've got a limited time to make a difference," she tells us.

Which brings her talk full circle, back to the Seven Seas and my trip mates, many of whom are board members of or big donors to Seacology, a Berkeley-based environmental organization dedicated to protecting islands and their surrounding waters. The ten-day cruise has taken 27 experienced divers on two boats—the Seven Seas and my boat, the Citra Bidadari, which are both well-appointed, 100-foot-plus modified Balinese schooners—on a vast loop through Raja Ampat, a group of islands northwest of Papua New Guinea. It has certainly been a pleasure cruise, the itinerary chock-full of dives and excursions, but it's also been a fact-finding mission for Seacology, which is touching base with several of its grassroots projects in tiny villages.

Already the culture shock has been extreme. I'm talking about my culture shock getting to know my fellow travelers. These are some rich folks, mainly from the upper strata of California's Bay Area and Silicon Valley—CEOs, IT wunderkinder, A-list attorneys of various stripes—many of whom have inherited wealth or else finished their work early and gone out to play, and who seemingly have no worries in the world, except the worry about the world. And while it may be easier for a dolphin to pass through the mesh of a tuna net than for a rich environmentalist to avoid the, um, inconsistency of a Sasquatch-size carbon footprint, the question remains: If not them (us), then whom? And if not here, then where?

Raja Ampat, after all, is the final frontier, one of the least fished, least populated, healthiest marine environments on the planet. It's also a place where worlds collide—politically, geographically, ethnologically, zoologically—every which way at once. Located just east of the famed Wallace Line (named for the great 19th-century naturalist Alfred Russel Wallace), which separates the fauna of southern Asia from that of Australasia, the archipelago is part of the 131,000-square-mile transition zone known to modern biogeographers as Wallacea. Scientists call Raja Ampat "the epicenter of marine biodiversity," where there are a number of endemics and where new species are discovered nearly every time a marine biologist straps on a tank. Properly protected, it could serve as a kind of evolutionary laboratory and maritime seed bank to jump-start recovery for the whole region and, potentially, in a pinch, the world.

But it's crunch time on the frontier. Historically, the four main islands—Misool, Salawati, Batanta, and Waigeo ("Raja Ampat" means "Four Kings" in Indonesian)—and more than 600 smaller islands and numerous cays have been protected by their remoteness. The tiny population of ethnic Melanesian Papuans, mainly subsistence fishermen, have been excellent conservators. But when they see big commercial boats from Sulawesi and other populous Indonesian islands whose own local waters have been depleted anchor offshore and wipe out the fish stocks with dynamite, they are tempted—indeed, forced—to blow up the reefs themselves to keep at least some of the profit at home. The genius of Seacology has been to cut a better deal for the villages by offering a customized quid pro quo: whatever they need—schools, community centers, solar power—in exchange for long-term protection of the priceless environment. Still, the pressure to extract the islands' wealth, coming from Indonesia's east-looking manifest destiny as well as multinational timber corporations, has been relentless. Seacology, Conservation International, and the Nature Conservancy have all entered into this war of wills as the situation in Raja Ampat has heated up.

"I prefer the term hope spot to hot spot," Dr. Earle says. "What I'm asking you to do now is hold up a mirror—see who you are, what you do best, how you can help. This is a big place. If we can save it, there's hope for the sea."