Sanggou Bay looks like a place where the pointillism movement has been unleashed on an ocean canvas. All across the harbor on China’s northeastern coast, thousands of tiny buoys – appearing as black dots – stretch across the briny landscape in unending rows and swirling patterns. They are broken only by small boats hauling an armada of rafts through the murky waters.

For centuries, Chinese fishermen have harvested this section of the Yellow Sea for its flounder, herring, and other species. Today the area is again producing a seafood bounty, though not from the end of a fisherman’s rod or the bottom of a trawler’s net. Instead, the maze of buoys marks thousands of underwater pens or polyurethane ropes that hold oysters, scallops, abalone, Japanese flounder, mussels, sea cucumbers, kelp, and garish orange sea squirts. They are all part of one of the world’s biggest and most productive aquaculture fields. Sanggou Bay is a seafood buffet on a colossal scale.

The buoys here extend for miles out to the horizon, offering, on an aluminum-gray day, the only clue to where the ocean stops and the sky begins. Hundreds of migrant workers – many from as far away as Myanmar (Burma) – pilot the fishing boats zigzagging around the floats, shuttling fish to shore, checking the lines for mussels and oysters, and voyaging farther out to sea to harvest seaweed.

“The bay is packed,” says Bian Dapeng, director of research and development for Xunshan Group, a state-owned Chinese conglomerate that controls much of the bay, as he looks out at the harbor from a rocky overlook. “Someday we’ll go even farther out.”

The transformation of Sanggou Bay from a struggling fishing port to an aquaculture leviathan symbolizes what may become one of the big food stories of the 21st century.

Aquaculture is the fastest-growing food-producing sector in the world – and China is a big reason why. The country has tripled its fish production over the past 20 years, making it the top producer, exporter, and consumer of seafood. China now contributes more than one-third of the global supply; 72 percent of its total seafood output comes from aquaculture.

Technavio, a global market-research company, predicts that China’s aquaculture industry will reach $100 billion – the size of the most recent Greek bailout – within the next four years, up from $66 billion in 2012. It’s expected to account for 38 percent of all fish for human consumption by 2030.

China’s dominance in aquaculture makes it inextricably linked to the industry’s future. Ling Cao, a postdoctoral researcher at Stanford University’s Center on Food Security and the Environment in California, says that how China develops its aquaculture sector will dramatically affect the availability of seafood across the globe.

“China has the power and influence in aquaculture,” she says. “It’s the 800-pound gorilla in this field.”

And aquaculture is no small field. Farmed seafood exceeded global beef production for the first time in 2011 and now provides about half of all fish consumed by humans. Population growth and an emerging global middle class have fueled an insatiable demand for seafood over the past half century. More people are eating more fish than ever before, leading annual consumption to double since the 1960s. With the global catch of wild fish stagnant, experts say, nearly all new seafood will have to be farmed.

Fortunately there appears to be plenty of room for aquaculture to grow. Oceans cover 71 percent of the planet but provide less than 2 percent of food for human consumption.

Aquaculture’s unrealized potential has led some scientists, economists, and policymakers to endorse it as one of our best options for feeding the world’s burgeoning population, which is expected to increase from 7 billion to 9 billion people by 2050. The challenge will be to do it as efficiently and sustainably as possible – while overcoming some of the nagging problems that have plagued fish farming in the past.

“I don’t know that anyone has a clear idea of aquaculture’s ultimate potential – it’s enormous,” says Hauke Kite-Powell, a research specialist at the Marine Policy Center of the Woods Hole Oceanographic Institution in Massachusetts. “We don’t have to come anywhere near using all of it to feed the projected world population over the course of this century.”

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The benefits of aquaculture are abundant. Rich in protein and healthy omega-3 fatty acids, fish are among the most nutritional foods in the world. They’re also among the most energy-efficient to grow. Roughly a pound of feed produces a pound of fish, while it takes nearly two pounds of feed to get a pound of chicken and seven pounds to get a pound of beef. What’s more, aquaculture’s carbon footprint is often a fraction of that of farming on land.

“Wake up,” says Christophe Béné, a senior policy expert at the International Center for Tropical Agriculture, who specializes in aquaculture. “You have scientists who have spent billions of dollars on trying to make potatoes richer in particular nutrients. Why spend thousands of millions of dollars when we have existing commodities that can do the trick?”

Yet aquaculture comes with a host of problems as well. Most fish farms around the world are in freshwater lakes or close-in coastal areas, and raising large quantities of fish in confined areas creates pollution from the natural waste the species produce. Both the pollutants and the networks of cages can harm fragile ecosystems, including coral reefs.

Environmentalists also worry about the potential for farm-raised fish to develop diseases and, if they escape their pens, imperil wild fish stocks. Many farm-bred fish are pumped up with antibiotics, which repels some consumers.

Then there’s the issue of fish feed – the major challenge facing aquaculture. The industry relies heavily on wild-caught species at the bottom of the food chain for the fish meal and fish oil needed to feed the farm-raised stocks. This has led to a decline in sardines, anchovies, and other natural forage fish. New feed made from soybeans and fishery byproducts has helped lower the dependency on overfished stocks, but experts warn much more work is needed to ensure fish farming can be expanded without despoiling the environment or depleting the oceans of other species.

“People are working very hard on making aquaculture sustainable because they know that we need to increase production in a way that doesn’t make things worse,” says Mark Spalding, president of The Ocean Foundation, a Washington, D.C.-based conservation group. “I’m cautiously optimistic. The question is how are we going to do it right.”

China exemplifies both the best and worst practices in the growing industry. Chinese fish farmers have polluted miles of coastal waters and contaminated countless freshwater lakes in the country’s rush to expand production. They’ve bulldozed huge swaths of mangroves to make room for shrimp farms, filled lakes cheek by gill with tilapia pens, and smothered reefs with net cages.

To feed these teeming schools, China has become the world’s largest importer of fish meal: It accounts for about a third of annual global trade.

Now, faced with overcrowded coastlines and dwindling sources of fresh water, China is beginning to move in a new direction. In 2013, the State Council, China’s cabinet, released a policy document that called for the “vigorous promotion” of sustainable aquaculture and the expansion of offshore fish farms. Both goals have become major components of China’s 13th five-year economic plan (2016-20), according to officials and researchers familiar with the drafting process.

“The future of aquaculture is in the sea,” says Dong Shuanglin, former vice president of Ocean University of China. “The challenge China now faces is to ensure a higher yield while saving energy, cutting carbon emissions, and reducing the use of fish meal.”

Dr. Dong and other experts warn that simultaneously achieving all three goals – in addition to reducing pollution – won’t be easy. But out in Sanggou Bay lies one possible solution gaining increasing attention. It’s called integrated multi-trophic aquaculture, a 21st-century name for a practice first developed in ancient China. About 2,500 years ago, Chinese farmers started to add carp to their flooded rice paddies. The fish would fertilize the rice and help eliminate pesky insects and weeds in the shallow waters before becoming food themselves.

In Sanggou Bay, fishermen have adopted polycultures for the modern age. They feed only the caged finfish and abalone, while the seaweed and other shellfish that make up the bulk of the bay’s production get their nutrients directly from the water. Those act as natural filters to help keep the bay clean by absorbing the large concentrations of nitrogen and phosphorus released by the fish. Meanwhile, the sea cucumbers that roam the ocean floor nibble on whatever organic waste floats to the bottom.

Integrated multi-trophic aquaculture presents a major shift for Xunshan. The company originally made its name in the wild-caught fishing industry. But three decades ago, after overfishing caused the Pacific herring populations to collapse, Xunshan reconsidered its approach to producing seafood. Farm-raised kelp has since replaced herring as its top seller; abalone and scallops come in a distant second.

“It was like going from hunting and gathering to agriculture,” says Mr. Bian, the company’s research-and-development director. “Fishermen here have all gone through this transformation. We call it farming the sea and raising fish in the pasture.”

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Integrated multi-trophic aquaculture has become the new frontier in aquaculture. The practice has sprouted up in coastal waters stretching from the rugged fjords of Canada to the tropical seas of Indonesia. Salmon farming has taken off in places such as Iceland and Norway. Shrimp farming is booming in Thailand and India. In August, the Peruvian government issued a decree that said boosting the country’s fledgling aquaculture industry was in the “national interest.”

Other countries are becoming more aggressive, too. In Russia, a company called Russian Aquaculture plans to invest $200 million in fish farming before 2020.

Even Big Agriculture has started to take an interest in the business. On Aug. 17, American food and agriculture giant Cargill announced plans to buy a leading Norwegian salmon-feed supplier for $1.5 billion. It was Cargill’s second aquaculture acquisition in two months. In July, the company unveiled a $30 million joint venture with Naturisa, a major producer of shrimp feed, to build a feed facility in Ecuador.

In the United States, fish farming is a modest but growing industry. About 75 percent of the operations are in fresh water – mainly harvesting catfish, trout, and tilapia.

Yet here, too, the industry is beginning to move into coastal waters. Shellfish farming is spreading in seaside communities across New England in particular. Consider the case of Dana Pazolt, a lifelong Cape Cod resident with a New England accent and a salty tongue.

Mr. Pazolt has been a lobsterman for 36 years. But in August 2013, he planted his first oysters as a way to diversify his income. His oyster farm has since become his primary focus.

“My hobby farm is turning into a full-time business,” he says one morning as he scoops penny-size oyster seeds into mesh bags. He then shuffles in chest waders into the shallow waters of Cape Cod Bay to load the bags into wire cages anchored just offshore.

Pazolt’s oyster farm is located in tidal waters behind the Sea Gull Motel, a single-story resort that his grandmother opened in 1958 but is now closing. He and his wife run a Pilates studio and the lobster boat.

Scratching out a living from the sea isn’t easy, as Pazolt’s calloused hands show. He’s fallen weeks behind in setting lobster traps and repairing oyster cages. To make matters worse, half of the oysters he had planted last year died, frozen under a thick sheet of ice that covered the bay.

Yet Pazolt seems undeterred. His goal is to plant 1 million oysters this year, up from the 330,000 he planted when he started two years ago. He also wants to quadruple the size of his one-acre farm and hire four full-time employees.

“The fisheries industry is boom or bust,” he says. “I’m trying to take that roller coaster out of my life.”

Yet fish farming brings its own challenges. It took Pazolt nearly four years and drawerfuls of paperwork to obtain the required permits to start his oyster farm. Expanding it will require even more letter-writing stamina. He blames the web of regulations for stunting aquaculture’s growth in the US.

The US controls more ocean than any other country, but 91 percent of the seafood eaten by Americans is from overseas. The growing demand for cheap imports has caused the US seafood trade deficit to rise to $11.2 billion in recent years. The US is the third largest producer of wild-caught fish in the world, yet ranks only 15th when it comes to farmed fish. Aquaculture meets less than 7 percent of the US demand for seafood.

“The US industry struggles to establish and maintain a foothold in part because of regulatory uncertainty and other challenges,” Kathryn Sullivan, head of the National Oceanic and Atmospheric Administration (NOAA), said in February at a sustainable seafood conference in New Orleans. “And as a consequence of that, we export advanced technology, feed, equipment, and other investments to producers around the world. It’s time we put a stop to that.”

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Thirty miles down Cape Cod from Pazolt’s oyster farm lies a hint of what the future of aquaculture could look like in the US. Last November, the US government issued the first permit to grow mussels in federal waters off the east coast. It leased 28.5 acres in Nantucket Sound, about four miles offshore, to a local fisherman. Authorities issued a similar permit for a mussel farm in federal waters off the coast of southern California last January.

Meanwhile, NOAA is reviewing plans to allow as many as 20 offshore fish farms in the Gulf of Mexico, and a private investment firm has partnered with the nonprofit research arm of Sea World to build a fish farm four miles off the coast of San Diego. Researchers consider the sites test cases for deep-sea aquaculture, which, if successful, could pave the way for future projects and help the US alleviate its dependency on imported seafood. Rose Canyon Fisheries, the planned farm near San Diego, will reportedly be able to produce 11 million pounds of yellowtail amberjack and sea bass each year.

“Nothing is going to happen fast,” says Michael Rubino, director of aquaculture at NOAA. “But hopefully we’ll learn during the next 10 years and be able to produce significantly more seafood in the future this way.”

China wants to push even farther out to sea. Last September, a researcher at Yellow Sea Fisheries Research Institute announced plans to retrofit a 200,000-ton oil tanker to operate as a floating fish farming village near Mischief Reef, a focal point of China's controversial land reclamation efforts in the South China Sea. Researchers from Ocean University of China are also planning to install fish cages in what they have dubbed a “cold water mass.” Located about 20 miles off the coast of Shandong Province in the Yellow Sea, the area is ideal for salmon farming.

About 6,000 cages are already being used to raise fish up to 16 miles off the coast of southern China, says Guo Genxi, a research fellow at the South China Sea Fisheries Research Institute. He adds that as technology improves, the cages will be able to extend 25 to 62 miles offshore.

Mai Kangsen, a top adviser to the Chinese central government on aquaculture development, talks about deep-sea fish farming with a scientist’s reserved optimism. It’s where he sees the industry heading, but he’s quick to point out the challenges in getting there. He’s well aware of the practical difficulties of growing fish in the open ocean: strong currents, high waves, and unpredictable weather. But he has no doubt that they can be overcome.

The same goes for the challenge of feeding 2 billion more people over the next 35 years. For Dr. Mai, it all comes down to a simple equation.

“To guarantee food security, we have to use less resources to produce more food,” he says. “Aquaculture is the most efficient way to do that.”

Back in Sanggou Bay, marine researcher Liu Hui is skipping across the water in a wooden skiff. She peers out at all the activity in the harbor as her boat weaves in and out of the hundreds of buoys, looking like pixels. In the distance, one boat pulls several wooden rafts, lashed together by rope, behind it – an ocean train headed out to collect seaweed. Men on other boats strain to pull up lines, checking them for shellfish.

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Ms. Liu has been coming here for more than 15 years. It’s long enough for her to remember when Sanggou Bay was a struggling fishing community. Now it sits in the vanguard of a possible global food revolution.

“Anyone who lived 30 years ago would be surprised by how far aquaculture has come,” she says, glancing across the bay. “It’s amazing to see.”