USC News

Menu Search

The Case for Fish and Oyster Farming

The Case for Fish and Oyster Farming
USC Wrigley Institute director Donal Manahan instructs sophomore Jonathan Sepulveda and freshman Isabelle Feldhaus as they prepare to take their first dives in the pristine water surrounding the institute.

Super corn and soybeans are so 20th century. With the world’s population nearing 7 billion on its way to 9 billion by 2050, marine scientists are looking for reliable new food sources through a Blue Revolution — the intelligent use of aquaculture to supplement depleted wild fish stocks with farm-raised oysters and other valuable ocean “crops.”

Why Fisheries Quotas Don’t Work
Collapsing Fish Stocks
Saving Salmon Through Hatcheries?
Farming the Supersized Oyster
Aquaculture: Do We Have a Choice?
Monitoring Algal Blooms and Fish Kills
Fertilizing the Ocean
More Food Through Hybrid Vigor

THERE ARE CYNICS who see only catastrophic answers to Earth’s population explosion: War and pestilence come to mind.

Then there are those who look a little deeper. Not even two feet deep, to be precise, into the placid tidal pools dotting the world’s coastlines. Like homesteads nibbling at the wilderness, coastal flats represent humanity’s creeping advance into the great, undomesticated Blue. It is on a coastal flat in the Pacific Northwest, along the quiet eastern edge of the Olympic Peninsula, that marine biologists from USC are pinning their hopes on the quest for bigger and faster-growing oysters.

Oysters? Oyster breeding is just one example of research projects at the USC Wrigley Institute for Environmental Studies in USC’s College of Letters, Arts and Sciences, all related in some way to the pressing dietary needs of our crowded planet.

But oysters? For the masses? Is this not the same elite delicacy served iced on the half shell in fine restaurants, or proffered to cuddly couples on Valentine’s Day? (Scientists, by the way, have not found any unusual stimulating substance in oysters: as with other alleged aphrodisiacs, the effects are in the mind.)

Unlike humans, Mother Nature takes oysters seriously. They pack huge amounts of protein, along with an alphabet soup of vitamins, lots of omega-3 fatty acids and hefty doses of minerals: calcium, iodine, iron, potassium, copper, sodium, zinc, phosphorous, manganese and sulfur.

All in one low-calorie package. It’s enough to arouse a nutritionist.

For marine biologists who wonder where humanity will find the next great meal, the oyster ranks high on the list of prospects.

“It’s not going to be krill,” deadpans Donal Manahan, director of the Wrigley Institute. Having tasted krill, he deems the small crustacean best left to a whale’s undiscriminating palate, along with smelt, phytoplankton and other floating detritus of the sea.

Oysters are not only more flavorful; they also exhibit a remarkable property known as hybrid vigor – possibly unique in the animal world – that could turn them into the Corn of the Sea.

And oysters are only the start, says Manahan. He calls for a Blue Revolution in all kinds of seafood to follow the Green one that boosted crop yields over the last century.

“We’re going to have to make future decisions as a society regarding how to provide enough food for a growing population,” he says. United Nations experts estimate that humans will number almost 9 billion by 2050.

“If you look globally, the untapped potential of producing more food from the oceans is enormous,” adds Hauke Kite-Powell, a research specialist at the Woods Hole Oceanographic Institution who sits with Manahan on a National Academies committee studying the issue.

Yes, they are talking about farming the oceans: aquaculture, or mariculture – by either name, still a sliver of the world’s farming output, and a dirty word to those who like their fish wild.

But as Manahan points out, how many of us insist on eating only wild game? These days we are happy if the chicken was allowed to strut. Most people do not even like meat with a “gamey” flavor.

In a few years, says Manahan, the world catch of farmed fish will surpass the wild-caught total for the first time in history. The most recent statistics show that in 2007, aquaculture supplied 42 percent of fish consumed worldwide. In the next year or two, that should hit 50 percent.

Prices bear out the trend. Even high-end farmed species such as oysters have come down since 1997 when compared to lowly wild Arctic fish like haddock and pollock – once staples of cheap cafeteria food, and still major ingredients in fish sticks and McDonald’s Filet-O-Fish� sandwiches.

Experiments performed by David Hutchins, another marine biologist in USC College, predict that ocean warming will shift the food web in the Arctic toward smaller organisms, reducing the food supply for the major commercial fish.

“It doesn’t look good up there,” Hutchins says. “It looks like the food chain is changing in a way that is not supporting these top predators, of which of course we’re the biggest top predator. There is some question as to how much of that is due to over-fishing and how much of that is due to climate shifts; probably they’re both involved.”

Why Fisheries Quotas Don’t Work

There are two ways to keep the oceans full of food for the future: Take less or make more. Can the first approach work?

So far it has not, although in theory quotas and conservation could help. Research on wild fisheries – the industry of catching, processing and selling the ocean’s bounty – centers on proper quota setting. How do you figure the right seasonal catch for a given fish?

The answer in the past often has been to fish until you can’t find any more, and you will know your quota was set too low. These are known as collapsed fisheries.

Which is why historical graphs of fish catches are known as “waterfall charts”: The catch is big and healthy for decades and then, suddenly, it dives like a barrel over Niagara’s lip.

Not surprisingly, scientists believe there is room for improvement. A better quota system requires knowledge of how and why some spawn survive while others die. Manahan works on those spawn, or what he calls “the seeds of the oceans”: the tiny, larval stage of fish.

Unlike humans, most fish create millions of larvae. In the wild, very few – nobody knows exactly what percentage – reach maturity. Manahan asks: “How many of these grow up and actually make a new adult? That’s one of the big debates in fisheries.”

Most quota systems take educated guesses at the recruitment percentage – the number of fish larvae that will reach adulthood. But if they miss by just a small amount, say half a percentage point, they can end up underestimating or overestimating by hundreds of thousands of adults.

Everyone has fiddled with a volume control that was too sensitive, where the slightest adjustment made the music too loud or too quiet. It’s the same principle, only the stakes in fisheries are real: Even a slight miscalculation can lead to the premature end of either the fishing season or, potentially, of the fishery.

“If you get those quotas wrong – and those quotas are affected by season, climate change, the food chain, a whole bunch of things – you’ve allowed a fishing quota that’s too much,” explains Manahan. “And poof, you’ve wiped out the fishery.”

Scientists agree that the larval stage is important. Few study it, however.

It’s not easy. The little critters are small – the diameter of a human hair – and as demanding as human babies. “They’re fussy,” Manahan says. “They have a behavior.”

The field was wide open when he first embarked on his career. “We knew lots and lots and lots about the adults but almost nothing about the babies. So I kind of decided I was going to become the pediatrician of these organisms.”

Manahan believes scientists know enough now to design much better quotas. The strategy depends on genetic profiling, to see which of the larvae have the right genes to survive bad seasons, environmental problems, unusually warm temperatures, algal blooms, toxins in the water and so on.

“There might only be 1 percent surviving, but it may not be just random luck that determines which ones make it,” he says. Maybe under some environmental conditions, a certain group makes it, and under other circumstances, it’s another group that survives.

This is the basis of classical Darwinian adaptation, the survival of the fittest. Knowing which traits make a larva “fit” gives scientists the tools to measure which offspring will thrive.

“And if they have the wrong trait, then your forecasting models would say they’re all going to be wiped out,” says Manahan.

Existing quota systems only account for the average response of a species to environmental variables, such as temperature. In a forthcoming paper, Manahan shows how particular subtypes of oysters grow better in warmer waters. It is an early proof-of-concept for his genetic profiling method.

Collapsing Fish Stocks

Some shellfish already show amazing adaptability. Recent research by Andrew Gracey, also on the faculty of USC College, shows that mussels can switch genes on and off within minutes to cope with the harsh conditions of the intertidal zone.

“It’s one of the most variable habitats on Earth,” Gracey says. “Mussels can spend part of the day bathed in cool Pacific seawater and the other part baked under the California sun.”

Finding the best genes for a given environment makes sense to other scientists. Up the coast, biologists at Oregon State University are studying the genes behind the temperature response of oysters. A disease linked to unusually warm waters wiped out millions of oysters earlier this decade.

Fisheries officials “have to make decisions that affect entire coastlines in some cases,” says Selina Heppell, a marine biologist in OSU’s department of fisheries and wildlife.

“Incorporating new information on the genetic structure of populations may allow management to become more regionally specific,” she says. “We may not be able to understand how everything works, but we can still do things in a better way.”

Heppell says management and quotas have improved, at least in terms of protecting fish stocks in coastal areas.

But are they enforced? Out on the open seas, how hard is it to find loopholes?

Manahan recalls an episode of the popular Discovery Channel reality show Deadliest Catch, in which crab fishermen labored 72 hours without sleep.

Why? Because the government quota restricts time on the water.

“So what do these people do? They increase the effort, and this is what is destroying the world’s [wild] fisheries. So now the models are having to account for effort.”

A now-famous paper by Boris Worm of Dalhousie University, published in 2006 in Science, predicted the total collapse of big fish stocks by 2048.

Catherine Purcell, a graduate student in the lab of USC College marine biologist Suzanne Edmands who studies striped marlin, knows how swiftly a stock can decline.

“I’ve seen the size of the fish change, even over the course of my Ph.D.,” she says. “These fish are strained.” And that’s for a species of only average commercial value. Imagine the damage being done to high-value fish like sea bass.

To keep up with marlin fishery trends, Purcell frequents catch-and-release recreational tournaments, where she trades her expertise for fin samples from trophy fish. “I kind of serve as a resident biologist in exchange for getting access to the samples,” she says with a chuckle. She also collects samples from commercial fisheries around the Pacific.

Dire as the situation seems, some of Purcell’s findings suggest a solution to an age-old dilemma. Conservation efforts have often foundered on narrow self-interest: Why should Island A ration its fishery when the survivors are likely to breed and feed and get caught off the coast of Island B, thousands of miles away?

Purcell has found that striped marlin are not interchangeable. The marlin from Japan, Hawaii and Southern California form one group. Those from Mexico, Ecuador and the Baja Peninsula mostly stick together, even though Baja and the Southland are next-door neighbors.

“What makes sense geographically isn’t what we’re seeing genetically,” she explains. The upshot is that if you are setting quotas for Southern California, you do not need to worry about fishing pressures down the coast. Your marlin likely won’t end up in those nets.

Purcell hopes her data will assist the Inter-American Tropical Tuna Commission, one of whose regulators serves on her thesis committee. “If the science is there, they want to be able to use it to make better decisions,” she says.

Les Kaufman agrees the science is there, and then some. A biology professor at Boston University who also studied marlin early in his career, he has been calling for fisheries management to be tailored to individual ecosystems.

“Many marine organisms produce tiny larvae that have the ability to move vast distances on ocean currents,” he says. “However, recent data show that a majority comes back to someplace near where they were born to seek a place to grow up.

“This means that if you remove the adult fish from a place, it may be a long time before young from elsewhere find their way there to reestablish the population that was decimated. Similarly, adults of many fish species can travel hundreds of thousands of miles, yet they return each year to a specific place to reproduce,” he says.

“Whatever their capacity to travel, fishes are stay-at-homes at heart,” Kaufman says. “The evidence for that is starting to be overwhelming and across the board.” That’s one little bit of science with the potential to change a lot of minds.

“If you take care of your backyard,” he promises, “you’ll get payback.”

Saving Salmon Through Hatcheries?

Salmon conservation is a rare and fairly successful example of “backyard management.”

Before moving into oyster research, Manahan’s collaborator Dennis Hedgecock, also a professor in USC College, advised state and federal officials trying to save the winter run of Chinook salmon in the Sacramento River.

It was the first salmon run to be listed as endangered. Eons ago, spawning salmon swam to the gravel beds of the Pit and McCloud rivers until construction of several dams, most notably Shasta Dam, blocked access. For their new spawning grounds, the winter Chinook picked a stretch of the Sacramento River in the middle of the city of Redding, Calif. The salmon run had plummeted from more than 100,000 returning adults to just 200 in the early 1990s.

The rescue plan relied on a hatchery. Hedgecock realized the program had serious genetic implications, and as the only researcher in the state with the required expertise, he quickly climbed aboard.

His first concern was genetic diversity. Hatcheries work like huge test-tube baby factories that mix millions of sperm and eggs. The risk is that, without careful monitoring, a single female may contribute a huge percentage of a season’s eggs. Males also can make disproportionate genetic contributions, as their milt can fertilize the eggs of several females. This can lead to inbreeding.

By 1995, Hedgecock and his colleagues and students had shown that the breeding program was well designed and, if anything, slightly improved the run’s diversity. But they had stumbled on a different problem: Without realizing it, the hatchery had been crossing winter- and spring-run salmon.

Since the whole point was to preserve the unique genetic heritage of a threatened species, the news dismayed regulators.

“They weren’t very happy with us at first when we told them they had done this,” Hedgecock recalls. Unavoidable conflicts with farmers over water rights make salmon conservation in California notoriously contentious.

Still, to their credit, officials agreed on the need to identify every fish brought into the hatchery. But how?

In the days before rapid genotyping, it was much easier to look at a group of people and classify them as either Caucasian, Asian or Latino than it was to figure out the genetic makeup of any one individual. The winter and spring Chinook all looked alike.

Hedgecock’s lab found a set of genetic markers to help with the ID process. For a few years, a fin sample for every fish at the hatchery was sent to Hedgecock’s lab.

Other laboratories started to develop similar tools and Hedgecock, feeling he had done his part, backed out gracefully. Years later, ensconced in his USC lab and wearing an appropriately salmon-colored long-sleeved shirt, he exudes relief.

“I couldn’t get out of salmon fast enough,” he says.

He also retains mixed feelings about hatcheries, which are far more common than people realize. About half of Alaska’s “wild” salmon come from hatcheries, he says.

Fish from hatcheries do not breed with wild fish. But they do compete with them for food. And hatcheries can produce lots and lots of hungry salmon.

Ironically, the very fish that were supposed to save wild salmon runs may be contributing to their demise.

“They could be constantly facing this competition against these hatchery fish,” Hedgecock says. “Maybe they’d have a better chance of surviving if they didn’t have to compete.”

He would prefer to see more emphasis on the harder approach to conservation: fixing and protecting the salmon’s native habitat.

To use a drinking-water analogy, hatcheries are like an extra shot of chlorine: easy, fast and cheaper for a city than making sure it has great water to start with.

“By the time you get to a hatchery, you’re desperate,” Hedgecock says.

If hatcheries are not the answer, and conservation or better quotas are only part of the solution, then where does one go to feed 9 billion people?

Farming the Supersized Oyster

Hedgecock and Manahan’s shift to oysters was prompted by a curious observation: Unlike any farmed animal, oysters exhibit hybrid vigor.

Consumers do not know or care about hybrid vigor. But we would if corn and wheat did not have it, because then a box of cereal might cost $20. (If we were still alive to buy it, after the food wars that would have erupted in the late 20th century as an exploding population ran out of food.)

Hybrid vigor, along with expanded use of nitrogen fertilizer, greatly boosted crop yields during the 20th century, increasing the average yield of corn per acre across the United States sevenfold.

It works like this (though still, no one understands why): If different strains of corn are inbred – forced to cross with themselves – the offspring look predictably small and withered.

But cross two different inbred strains, and their offspring sometimes explode in size, outgrowing not just their inbred parents, but also their vigorous grandparents.

By trying thousands of different crosses, seed companies have developed healthy varieties that dwarf the corn farmed during the early part of the last century. And every year, new and slightly bigger or faster-growing varieties come to market.

The process has an obvious limit: No amount of hybridization can extract more than the soil’s available energy. As crop improvements approach the land’s maximum yield, the world’s population continues to grow exponentially.

Maybe it’s time to look beyond the land.

Hedgecock is sure that oysters have hybrid vigor. He has bred some to grow twice as fast as their wild ancestors.

In a 2007 paper in the Proceedings of the National Academy of Sciences, he and Manahan, along with scientists at biotech giant Solexa, identified 350 genes involved in oyster growth. (In a follow-up study published in 2010, Manahan proposed an explanation for differences in growth rates.)

Yet even now, Hedgecock knows of no other lab working on hybrid vigor in oysters. He attributes this scientific incuriosity to the challenge of actually demonstrating hybrid vigor. To do so, a researcher must be able to breed hundreds of millions of baby oysters, and then find a commercial farm willing to grow them outside the lab.

Hedgecock has done both. His lab’s research caught the eye of Joth Davis, head of research and development at Taylor Shellfish Farms, located on the bays and inlets of Washington’s Puget Sound.

Few farms have their own R&D department. But Taylor, one of the world’s largest growers of shellfish, is also one of the most progressive. At a December 2007 meeting with Hedgecock and Davis, owner Paul Taylor agreed to commit time and space for growing Hedgecock’s hybrids.

Currently the operation is testing three varieties and focusing on one. “This particular hybrid cross is great,” Davis says. Having watched the lab specimens grow bigger faster, he expects the harvest, due in 2011, to fulfill its promise.

Taylor plans to sell the 5 to 8 million mature oysters that result from the project, keep 90 percent of the seed for in-house breeding, and offer the rest to other growers.

And there’s better stuff to come.

“Almost any time we make an inbred line and we cross them, their offspring are better than their inbred parents … and often they’re better than wild,” Hedgecock says.

Oysters even pack an attractive bonus for those worried about toxic algal blooms. Research on algae points to nutrient runoff from urban areas – mostly sewage and lawn fertilizer – as a possible cause.

It turns out oysters are especially good at recycling such nutrients, says Kite-Powell, Manahan’s colleague on the National Academies mariculture committee.

“This is a natural filtration process that is reasonably well understood,” he says, adding that “it’s a piece of the answer; it’s not by any means a silver bullet.”

But in some cases, it seems that oyster farming “is actually an activity that pays for itself while performing this ecosystem service.” (A recent National Academy of Sciences report on mariculture exonerates an oyster farm from charges it harmed the environment. See press clips here).

More controversial is the farming of so-called fin fish like salmon.

“They’re like floating pig farms,” Daniel Pauly of the University of British Columbia told the Los Angeles Times. “They consume a tremendous amount of highly concentrated protein pellets and they make a terrific mess.”

But even that type of farming should not be dismissed out of hand, Kite-Powell says. It is true that farmed salmon require several times their weight in animal feed over their lifetime. On paper, that makes farming salmon wasteful. If one thinks of fish as energy-storage vehicles, every transfer of energy from a plant to the fish that eats it, or from that fish to a bigger predator, entails some loss. It would be more energy efficient to go straight to the source.

But if we are going to eat salmon, the farmed variety may be on aggregate less energy intensive. As Kite-Powell points out, “The alternative to farming it is to catch the wild salmon, and wild salmon consume a lot more animal meat proportionately.”

We may find ways to grow food from the oceans “less destructive than many of the practices we employ on land,” he suggests. Some have even proposed giant floating cage systems that would drift with the currents.

Granted, the most ecologically friendly approach would be to eat only shellfish and vegetarian fish. But that would require certain adjustments in the American diet.

Carp, anyone?

Aquaculture: Do We Have a Choice?

The notion of farming the sea takes some getting used to. The committee that Manahan and Kite-Powell serve on is studying, among other things, a conflict between oyster farmers, park visitors and residents in Northern California’s Marin County. Similar conflicts might occur among residents of Malibu if sea pens were proposed for the waters off their beachfront homes.

Manahan is not unsympathetic. The crashing waves of the sea were the soundtrack to his childhood in Dublin, Ireland, where his family lived in a fort built on a rocky point during Napoleonic times, a lookout against French invasion. The world was less crowded then, the seas more bountiful. Everything has changed, but at least the ocean outside his ancestral home seems the same.

How would it feel to look out of the stone casement and discover a domesticated bay? How would a nation whose poets rhapsodized about the ocean, but which lost millions to a potato famine, react to large-scale farming of the coastline? How would this nation?

But, Manahan says, “We can’t just sit here and do nothing. What’s going on now is an infinitesimal drop in the ocean of what will happen if there’s a climate shift. You think the cost of food is expensive now? Wait until rainfall patterns in the Midwest change.”

Manahan, who became director of the USC Wrigley Institute in 2008, plans to focus to a large degree on “food, energy and water.”

“And don’t think they’re not linked,” he warns.

He believes the generation growing up today will hear politicians talk about food the way they now talk about oil. “We need to grow our own” may replace slogans about drilling for oil, he says. “Because when it comes to aquatic foods, we have no policy.”

Manahan recalls a quote by Arthur C. Clarke, the great science-fiction writer, who wondered why we call this Planet Earth. The better name would be Planet Ocean, since seawater makes up 99 percent of the biosphere.

Someday, our descendants will wonder how we got by on 1 percent.


Monitoring Algal Blooms and Fish Kills

algal blooms.jpgA good farmer makes it his business to know all about soil.

A good mariculturist is no less interested in understanding the local waters.

Marine scientist Burt Jones and his students at the USC Wrigley Institute were investigating just that when one of the submersible “gliders” they use to monitor water quality came up for air off Dana Point last summer.

The torpedo-like gliders swim around the South Coast for weeks at a time, letting the current do the work and using a small battery pack to steer, dive and rise. Every now and then, they surface and transmit their data to Jones’ lab via satellite link. Then they dive again.

Except this time a glider did not obey the dive command. Instead, the automatic tracking system showed it moving unusually fast.

It occurred to Jones that the glider’s speed was similar to a fishing boat’s.

Hours later, a full swordfish boat sailing into Catalina was met by the harbor master, who in the name of science repossessed the bright yellow glider lying on the deck. Thinking it disabled, the fishermen had picked it up.

“I think they were a little bit surprised when they found out we were following them all day,” Jones recalls with a laugh. “I don’t think they like to reveal where they were fishing.” Adding to the crew’s disappointment was their dashed hope for a reward.

Memo to South Coast fishermen: Throw back the glider and make room for another swordfish. You’ll make money and help science.

Barring future abductions, Jones and his students plan to continue measuring key indicators in coastal waters – such as temperature, salinity, chlorophyll, suspended particles and nutrient levels – both with the gliders and with several buoys and moorings.

One of their top priorities is early detection of algal blooms. Some of these have made news in recent years because they produced a deadly toxin – domoic acid – that causes disorientation and death in sea lions and other marine animals.

“A bloom may not be apparent at the surface,” Jones says. “It may be that the glider will see it but a satellite wouldn’t.” “We use all these resources because they all give us different pieces of information.”

USC College’s David Caron is the best-known California authority on algal blooms.

“We pretty much know that the number of these blooms is increasing, and the severity of some of them also appears to be increasing,” he says, citing nutrients from sewage and urban runoff as two prime suspects.

Caron cautions that the causes of algal blooms remain unclear: “It’s not one specific thing that gets into the water and, ‘boom,’ you’ve got a bloom,” he says. What he knows with certainty, though, is that “we can no longer think of the ocean as our great dumping ground.”

Fertilizing the Ocean

sea fertilizer.jpgNitrogen fuels plant growth everywhere, but out at sea, another nutrient plays the starring role.

Iron is the scarcest vital nutrient in most areas of the oceans, say researchers with the USC Wrigley Institute for Environmental Studies. That makes it potentially the most interesting.

James Moffett, a professor of biological sciences in USC College, has been studying highly productive areas off California, Peru and in the Arabian Sea. At least in the Arabian Sea, he is finding that the zones with the most aquatic life are iron-limited. They are productive because other nutrients are plentiful.

Would they be even more productive if iron were added? Could less-productive areas also get a boost?

The question of “iron fertilization” continues to split the scientific community. Some scientists have called for iron to be used at sea as nitrogen was on land during the Green Revolution: as a stimulant to boost plant growth and, as a bonus, to remove additional carbon dioxide from the atmosphere.

Others warn that iron fertilization would have unforeseen consequences, including production of other greenhouse gases and wholesale changes in the food web.

Moffett and others caution that excessive stimulation of productivity can backfire, as rapid plant growth depletes the water of oxygen, causing massive fish kills.

Moffett is more interested in subtle changes in ocean chemistry from events on land. For example, drought caused by global warming, or agricultural mismanagement, can affect the amount of iron blown or carried into the sea.

“My work creates linkages between phenomena that were not suspected to be connected before,” such as the connection between drought and ocean productivity in the Arabian Sea, Moffett says. He plans to conduct a large cruise off iron-starved waters in Peru to confirm his findings.

Another USC Wrigley scientist, Douglas Capone, published research in 2008 in Proceedings of the National Academy of Sciences suggesting that iron fertilization in tropical waters could boost plant growth while avoiding some of the risks. Because the water in the deep tends not to mix with surface water at the tropics, those oceans should be able to keep captured carbon solids from returning to the surface in the short term, he says.

“The most appropriate places are probably not the high latitudes,” he adds, “but rather the low-latitude tropical areas.

“If we choose as a human society to fertilize areas of the oceans, these are the places that probably would get a lot more bang for the buck in terms of iron fertilization.”

And in a recently published study in Nature Geoscience, Katrina Edwards of USC Wrigley showed that iron fertilization may be occurring naturally, and from an unlikely source. Edwards and colleagues found that some iron emitted by hydrothermal vents at the bottom of the ocean can be captured by organic solids and carried away in seawater, potentially feeding life near the surface.

More Food Through Hybrid Vigor

hybrid-vigor.jpgNothing good can come from inbreeding, we have been told. But were it not for inbreeding of crop lines, humanity might have run out of food already. In 1908, George Harrison Shull of Cold Spring Harbor Laboratory showed that two inbred lines of corn could be combined to make a plant that was not only healthier than its inbred, shriveled parents, but also bigger and faster-growing than the healthy plants that were combined to make the inbred lines.

This is known as hybrid vigor. Offspring of crossbreeds usually do not exceed their parents consistently in size or growth rate. Yet oysters can and do, suggests research by Dennis Hedgecock’s group at USC. That may someday make them the Corn of the Sea.

If you have questions or comments on this article, please send them to To view a video about The Wrigley Institute for Environmental Studies, visit

The Case for Fish and Oyster Farming

Top stories on USC News