This is a transcript of the Gastropod episode The World Is Your Oyster: How Our Favorite Shellfish Could Save Coastlines Worldwide, first released on April 2, 2024. It is provided as a courtesy and may contain errors.

JOE MATTHEWS: So this is the Nature Conservancy reef. It’s—I think it’s almost two miles. You can see it sticking up. The tide’s so low that we’re having trouble getting close to it. But you can see all that growth on them? Oysters. That’s oysters.

CYNTHIA GRABER: I’d never seen oysters growing out in the wild, this was exciting!

NICOLA TWILLEY: I was this close to hopping in and harvesting them myself! We love oysters here at Gastropod. And Gastropod is what you’re listening to! We’re the podcast that looks at food through the lens of science and history. I’m Nicola Twilley.

GRABER: And I’m Cynthia Graber, and we were on a boat floating only a few feet away from a man made oyster reef, not just because we really do love to eat oysters, it’s true we do, but because we wanted to know why groups around the country are spending millions of dollars to create new homes for these tasty bivalves.

TWILLEY: Oysters are always the answer to the question of what to eat, but are they also the answer to some of the biggest problems facing coastal cities today?

GRABER: This episode, we consider the oyster. Why Americans used to be in love with it, how we kind of fell out of love, and why reigniting that passion is not only good for us, but also might help save the world.

TWILLEY: This episode is supported in part by the Alfred P. Sloan Foundation for the Public Understanding of Science, Technology and Economics, and by you, our fabulous listener supporters. Gastropod is part of the Vox Media Podcast Network in partnership with Eater.

[MUSIC]

GRABER: Last episode, we were eating our way through southern Louisiana, in part because of the incredibly biologically rich delta, the coastline that’s unique in the world. And to talk about oysters, we have to talk about that coast, because what we didn’t tell you is that the Louisiana coastline is under threat. You might remember Boyce Upholt from our most recent episode, he’s the author of The Great River.

BOYCE UPHOLT: I mean, very famously, Louisiana is disappearing, and we are losing our marshes at an incredibly rapid rate.

SETH BLITCH: We lose about 16 square miles of coastal wetlands annually.

TWILLEY: That second voice, that’s Seth Blitch, he’s Director of Conservation for the Nature Conservancy in Louisiana. And the long and short is that southern Louisiana is one of the fastest disappearing places on earth.

GRABER: So why is Louisiana losing all those wetlands? Well, in our last episode, we talked about how amazing the marshes are in the delta, and how they’re created by the Mississippi River flowing down into the Gulf, and the Gulf gently pushing back against it.

TWILLEY: The mechanics of this are all to do with mud. The river carries a boatload of mud. It’s basically hundreds of millions of tons of sediment that has washed off the surface of Illinois and Missouri and Kentucky, and all the other states whose watersheds drain into the Mississippi, which is 40 percent of all the US.

UPHOLT: But a key factor in that is the way the marshes were built was, floods came and they kind of, you know, mud washed over and settled into these bays and built up.

GRABER: All of the Mississippi delta—all of Southern Louisiana—is built out of this mud.

UPHOLT: And then over time that mud, it’s just sitting on top of more mud and like mud on top of mud, it’s just going to kind of sink.

TWILLEY: And it’s also going to erode, because it’s soft and new, and because salty Gulf waves are eating away at it.

BLITCH: And salt marshes are, by their nature, sort of ephemeral, you know, they, they come and go and change position over, over time.

GRABER: So far, so good. The river meanders and floods and drops mud to build land, the mud sinks and the sea erodes, but these things are happening kind of in equilibrium.

TWILLEY: What that means is, left to its own devices, the Louisiana coastline would change shape, the maze of bayous and swamps and islands that made it so hard for early Europeans to explore would move. But it wouldn’t necessarily change size—things would just shift around following the river and its mud.

GRABER: But we did not leave it to its own devices.

UPHOLT: The big thing is this levee, right? On the lower Mississippi River is about a thousand miles of river and there’s—somehow the Mississippi River and Tributaries Project is the official name for the system of flood protection. I think it’s 3,700 miles of levees.

GRABER: Way back when, colonists loved the rich land along the sides of the Mississippi and they set up farms, but they didn’t like the river’s seasonal flooding—though of course it was that flooding that made the land so rich in the first place, but never mind.

VOICEOVER: Sometimes the giant gets out of control. Sometimes the rich valley lies helpless, defenseless against great floods, which leave terror and destruction in their wake.

GRABER: This is from a US Army Corps of Engineers movie from the 1940s about taming the river.

VOICEOVER: The broad flood control plan was no overnight accomplishment. It took years of careful planning and exhaustive investigation. Specially trained engineers mapped and studied the Mississippi and its tributaries, measured the valley of the giant for size, and cut the control pattern accordingly.

TWILLEY: The biggest element of this so-called control pattern were the thousands of miles of levees that Boyce mentioned. These are basically giant walls to keep the river fixed in one place and stop it from overflowing and meandering and carving new paths, the way it always had. And when I say giant, I mean giant.

UPHOLT: It’s just just a massive thing. There’s, there’s not much else on earth quite so big as this.

GRABER: Levees aren’t the only engineering we’ve done to the river. We’ve also dug some pathways in the river to cut off bends and loops. We’ve put in pumps and gates to create storage, and also systems for when there is some flooding, to direct that flooding.

UPHOLT: In some ways, the Mississippi River, the lower Mississippi River is this giant machine.

TWILLEY: The previously untamed Mississippi now flows through one of the most highly engineered river basins in the world. Truly impressive work, team human!

VOICEOVER: Agriculture will flourish unharmed. And the people of the valley will prosper. Cities formerly ravaged by flood will grow stronger under the protection of the great levees. And so the future becomes one which holds new promise for the valley and the nation.

TWILLEY: We showed this river who’s boss, am I right?

GRABER: Well, we did stop most of the floods. But also, now all that mud, instead of getting gently deposited on the delta, it gets funneled along with the rushing river all the way out into the Gulf of Mexico.

BLITCH: And so, in the absence of new sediment coming down, we had erosion without any real accretion or building of land back.

TWILLEY: And then to add to all that natural erosion and unnatural lack of replenishment, sea levels are rising.

GRABER: Sea level rise is caused by climate change. It’s a problem for all coastal cities. But it turns out that sea level rise is happening along the coast in the Gulf of Mexico faster than anywhere else in the world, thanks to a combination of warmer water and wind circulation patterns.

TWILLEY: Combine the rising sea with the sinking mud, and the result is not pretty.

BLITCH: We have the highest rate of relative sea level rise on the planet. And relative sea level rise is just the rate at which sea level increases, coupled with the rate of subsidence. And so, you know, the land mass is moving down and the sea level is moving up. And so that—again, compared to anywhere else, it’s, it’s pretty profound.

TWILLEY: But wait that’s not all. There’s more!

UPHOLT: The big one is oil and gas drilling and canal digging.

GRABER: Oil and gas is pumped out in the gulf, and they have to get it inland to a refinery so they can process it. To do so, companies dig out canals, and this allows salt water to encroach inland into the marshes. The salt water kills the local plants, and then those plants can’t hold the marsh in place, and it starts disappearing even more.

UPHOLT: That is a really big piece of it. The numbers vary, but in some federal documents, there’s estimates as high as like 60 percent of land loss could because of oil and gas activity.

TWILLEY: And all of this combined is—well, it’s basically a slow motion disaster.

MAN: Louisiana has lost an area greater than the Grand Canyon.

MAN 2: Given some of the sea level rise predictions, we could lose double that over the next 50 years.

MAN 3: It’s an economic disaster waiting to happen as well.

MAN 4: We power this nation, we feed this nation, we provide all sorts of commerce for this nation. This is a national issue.

UPHOLT: And so that is the crisis that we have today where we’ve lost, you know, more land than the state of Delaware. We’re losing a football field every hundred minutes.

TWILLEY: A football field-sized chunk of Louisiana is vanishing into the water every hour and a half. Frankly, that’s bananas.

GRABER: Obviously there are a lot of problems with losing this much coastline. But one of the biggest problems for us humans has to do with the weather.

BLITCH: Louisiana is like a magnet for hurricanes. If there’s one in the Gulf, we’re going to see it. And, and so. As you start to lose those coastal wetlands… there’s less land to sort of break up and dissipate the force of that storm and absorb some of the wave energy and dampen some of that tidal surge.

BLITCH: And so the more we lose coastal wetlands, the more our risk increases and the more resilience decreases in some of these areas.

TWILLEY: This of course, is a particularly bad time to be losing that coastal buffer, because climate change is making hurricanes both more common and worse

UPHOLT: You know, here in New Orleans, we get—I’ve lived here for five years and I should be able to count the hurricanes, but like I stopped counting.

GRABER: More destructive hurricanes are obviously not the only issue when it comes to losing coastline. Losing wetlands also means losing the home for all that incredibly rich biodiversity we told you about last episode.

BLITCH: You know, Louisiana has, you know, I described has this really rich system of coastal wetlands, which create a lot of productivity. You know, I mean, we still produce more oysters commercially than any state in the country, I think. And we have a rich seafood tradition here.

TWILLEY: But when you lose the marshes, you lose the places where all those baby shrimp and fish hang out and all the food that nourishes them.

GRABER: And so for a couple of decades now, the state government and local nonprofits and scientists have all been trying to figure out what to do about this. The state has created an official coastal restoration master plan.

BLITCH: And some of the things featured in that plan are things like, ways to reconnect the Mississippi River specifically, and its freshwater and sediment back to the coast.

TWILLEY: Some of these schemes are really expensive and complicated. There are plans afoot to build giant mechanical gates into the levees so that engineers can siphon off a little of the water, plus its precious mud, but not too much, and then let it flow out into the marsh to help rebuild it. The price tag for these projects is astronomical, and they’re super complicated—because we’re trying to mimic what would have happened naturally in a totally controlled and artificial way.

BLITCH: So that’s one way. The state is invested in just moving sediment itself around to help shore up or rebuild or even create barrier islands. Which can act as a natural defense.

TWILLEY: There are also plans to plant mangroves and native grasses and trees to help stabilize the existing marshes.

GRABER: And then much to our delight, there are oysters!

BLITCH: Oysters actually has figured into the master plan.

TWILLEY: Oysters, the mollusc in shining armor. But really? Oysters?

GRABER: Let’s get to know our hero. Like Nicky said, at its most basic an oyster is a mollusk. Its armor is not actually so shiny, at least on the outside. It has two kind of rough tough shells that are glued together by a sturdy muscle. And the main oyster body inside is a soft grayish delicious blob.

TWILLEY: There are a few different kinds of edible oysters that are commercially available.

GREENBERG: Any oyster that you’re eating on the East coast is going to be, Crassostrea virginica. That’s a single species. So even though you might have an oyster that’s called, you know, a Peconic or a moonstone or whatever, they’re all that same species.

GRABER: Paul Greenberg has been on Gastropod before, he writes about seafood and he wrote about oysters in particular in his book American Catch.

GREENBERG: The ur-species of oysters that Europeans adapted to eat or grew fond of eating is Ostrea edulis. It’s sometimes referred to as the ‘true oyster,’ even though it’s just, you know—tell that to the Crassostrea.

GRABER: This European oyster is harder to find in the US, though I’ve had one before, it was farmed in Maine. It did taste different from the other east coast oysters I usually eat: it’s weirdly a little metallic. It had an aftertaste kind of like licking a penny. But it still was really good!

GREENBERG: And then, there is another oyster on the west coast that is actually not native to the west, west coast. So that oyster was brought in to the west coast of the United States when the native west coast oyster, the Olympia oyster, went bust.

GRABER: The Olympia oyster was nearly wiped out by overharvesting and pollution, but today it’s being brought back.

TWILLEY: In our endless quest to eat all the oysters, we’ve tried the Olympia too, it’s lovely—very small, with a sort of nutty, earthy flavor. And it also has a little bit of a metallic aftertaste.

GRABER: But for a while the Olympia was nearly gone. In the early 1900s West Coast oyster growers who wanted to revitalize the industry started to experiment with a fast-growing oyster called the Pacific oyster, which they brought over from Japan, and that’s now the main West Coast oyster. Pacific oysters are less salty than east coast ones, and they have a kind of cucumber note to them.

TWILLEY: To add to the mix, there’s also the kumamoto, which is a smaller Pacific oyster that for a long time people thought was the Pacific oyster, but then they recently realized is a separate species. There’s also Sydney rock oysters, which are harder to find, at least in the US.

GRABER: All these oysters taste different—not just because they’re different species, although that’s part of it.

GREENBERG: Every variety of oyster from every part of the ocean that you might eat tastes a little differently because of the sea in which it, it exists.

TWILLEY: That’s because oysters eat by drawing salt water across their gills, which basically filter out the little bits of organic matter and nutrients they need. All day, every day, a hungry oyster is cracked slightly open, just marinating in all that salt water, so the saltier the patch of ocean an oyster lives in, the more briny-ly refreshing it will be.

GRABER: The saltiness changes, but also the flavor changes too. For one, the time of year affects what an oyster tastes like—in the spring they’re eating a lot and growing really fast so they’re kind of milder tasting. And depending on the type of green stuff in the water that they’re eating, they could have a more vegetal flavor.

TWILLEY: Sweet or salty, vegetal or minerally, they’re all freaking delicious and if you don’t believe me, listen to Ernest Hemingway. Paul told us a very relatable oyster story from Hemingway’s memoir.

GREENBERG: Hemingway’s been sent out by his wife to get some firewood, and instead he blows all the money on a dozen oysters and some wine, and he says something like: As I ate the oyster and drank the crisp wine, I lost the empty feeling inside and started to make plans.

GRABER: I certainly am happier once I’ve had some oysters and great wine and no longer feel empty inside.

TWILLEY: People have been filling the void with oysters for a long time. Our earliest ancestors weren’t necessarily writing memoirs like Hemingway, but they were leaving behind clues to their oyster consumption in the form of lots of empty shells, piled high in trash heaps called middens.

GREENBERG: They have found shell middens that are over 100,000 years old. They found them off of Africa. They have found—and not just oysters, all sorts of shellfish. But because, mollusks like oysters and clams—and mussels—are quite high in omega-3 fatty acids, there is an argument that’s been made is that the access to that high, rich source of omega-3s could have potentially improved our cognitive abilities and helped us kind of move on as a species to the next level.

GRABER: Whether or not oysters and other shellfish helped launch our big brain revolution, it’s definitely true that everywhere around the world where there are oysters, people eat them. And they kind of always have.

TWILLEY: But while the thing we care about the most is how delicious oysters are, for the purposes of saving the world, and also maybe stopping Louisiana’s coastline from disappearing, the thing that really matters is that oysters build reefs.

GRABER: And this particular skill of theirs has to do with the very exciting oyster lifestyle. That story, after the break.

[BREAK]

BLITCH: On paper, it looks really boring. The oyster’s life. But I mean, oysters have been around for millions of years, so they’re successful, you know, as an animal. I mean, what they haven’t done is destroy their own environment, you know, right?

TWILLEY: Fair. So what is the secret of their success?

GRABER: Darrah Fox Bach is another one of our oyster experts this episode, she works for the Coalition to Restore Coastal Louisiana.

DARRAH BACH: Well, oysters release their eggs into the water column, and they float around for a surface to attach themselves to.

BLITCH: And as they start to put on shell, they become too heavy. And so they’ll sink.

TWILLEY: But they don’t just sink anywhere. They look for clues that they’re going to like the spot they sink onto.

GREENBERG: Probably the most favorite place of an oyster to live is where other oysters live. So when you have oyster shell on the ground, and that’s often referred to as culch, they like to attach themselves to that.

BACH: The adult oysters will release physical and chemical cues to show the baby oysters that there, it’s a suitable habitat. They all settle there. And then they grow, around each other and on top of each other, and they really cement themselves together as they grow this hard calcium shell.

GREENBERG: And that’s basically what they’re going to do for the rest of their lives. Filter phytoplankton, live off that phytoplankton, grow bigger to the point at which hopefully, if they’re in clean water we can eat them. Which of course is not their sole purpose on [LAUGHS] on Earth, but that is certainly one purpose that humans like them for.

GRABER: It’s helpful to us that oysters grow in reefs so we can find a good meal all in one place, but the oysters like to grow in reefs because it actually helps them feed more efficiently too.

BLITCH: As oysters increase the size of the reef and the height of it, that displaces water. And so the same volume of water has to run around the reef.

TWILLEY: Funnel water around an obstacle, and the water will move faster, that’s physics. And, like we said, oysters feed by drawing that nutrient filled water through their gills, so the faster the water moves, the more nutrient filled water flows by for them to draw in and feast on. Basically a reef is a nutrition optimization scheme for oysters.

GRABER: But reefs help us, too, and not just because they serve as a great buffet. The oysters keep piling on top of each other with all this hard shell, and that shell helps stop waves from crashing into the shore. And that helps protect the coast when there are storms, and it also helps prevent erosion.

TWILLEY: Honestly oyster reefs, they really help everybody. Not just the oysters and us, but all kinds of other creatures.

GREENBERG: The other thing oysters do is they provide a lot of cover for microorganisms and forage for macro-organisms.

GRABER: Microorganisms and macro-organisms—that means little tiny creatures and the bigger creatures that feed off them. Because an oyster reef isn’t just home for oysters.

BACH: So we’ve got fish feeding off the, the algae that’s growing on the reefs. We’ve got barnacles and mussels and clams. Sometimes we even see like crawfish that, that enjoy the reef habitat. Birds land on the reef, so it’s part of the flyway, you know, system. So, oysters are really important for, for ecosystems and habitat.

TWILLEY: Oysters are really kind of like a magic multitool. Because it’s not just the reef structure that is so helpful, it’s also that a reef full of oysters is basically a giant Brita filter for the ocean.

BLITCH: Mature oysters in the lab can filter up to— you know, 50 gallons a day is the term that gets thrown out there. I like to say they probably just do more like 20 a day. But again, you know, 20 gallons a day times hundreds of thousands of oysters. That’s a lot of filtration.

GRABER: We described how oysters pull the water in and suck the nutrients they want to eat out of that water—well, that’s literally how they filter water. They feed off all the tiny little stuff in the water, and then they turn that into their body, into the shell, into the reef.

GREENBERG: And this is actually super important from a kind of ecosystem-based perspective because when the water is clear, more sunlight goes in and it will stimulate the growth of things like eelgrass.

TWILLEY: And eelgrass also provides essential habitat for all sorts of baby fish. Ecology, man, it’s really all connected.

GRABER: So oysters in the wild just keep adding to their reef homes. Seth told us in theory living reefs can survive for thousands of years.

TWILLEY: And over that amount of time, they would get really rather large. Boyce told us that historically, the oyster reefs off the coast of Louisiana formed an actual physical barrier, a sea wall of sorts.

UPHOLT: Ships would come in and be like, oh man, how are we, how are we going to get into this river? The, the oysters are so thick that it’s just going to like, tear our boat to shreds.

GRABER: Oyster reefs and the oysters that were living on them were massive. And not just in Louisiana, but everywhere oysters liked to live. Paul described what it was like around what’s now New York City.

GREENBERG: Yeah, there were huge reefs of oysters, not just oysters of the size that we’re used to eating, but huge oysters, as big as a plate. I think it was Swift who said that eating an American oyster was like eating a baby. Just… kind of gross. And that, you know, you’d have to take a knife and fork to it.

TWILLEY: Paul says that the oyster reefs in New York were so big that they stretched for miles, they rose above the surface of the water, and New York Harbor was a lot shallower as a result than it is today.

GRABER: And Native Americans who lived by the coast loved to eat them.

GREENBERG: There are huge amounts of shell middens and piles that we find all the time, around estuaries up and down the East Coast. But, none of those native societies had the industrial capability to really completely mine out an oyster ground.

TWILLEY: Whereas the European colonists very definitely did. They loved oysters too.

GREENBERG: Well, New Yorkers ate a lot of oysters. By some estimations, something like 600 local oysters per person per year. This is going back to the, you know, this is like, late 18th, early, 19th century.

GRABER: I would love to eat 600 oysters a year, personally. But this massive oyster fest had two big problems—one, New Yorkers were just eating too much of them, faster than the oysters could replace themselves. And two, they didn’t drop all those oyster shells back in the harbor around the reefs so that baby oysters had a place to land and grow.

GREENBERG: They were devastating to the reefs. And it was a kind of pernicious thing where the oysters were used against themselves. When you harvest an oyster and you eat it you have this shell left over, and the shell is actually quite useful.

GRABER: Oyster shells are particularly useful in construction. You can burn oyster shells to make lime, which is a critical component of mortar. And that mortar was used to build vertical walls along the coast to protect the city from the water.

GREENBERG: And a vertical wall is actually very hard for an oyster to recolonize. They like a gradual slope. So, in effect, we armed the coast against oysters. So it, it almost is, you know, in that, It’s a horrible human way of really messing things up for everybody, we used the oyster against itself. And in effect, converted the ecosystem from a very, layered, textured environment to a big slick of mud.

TWILLEY: In Louisiana, the same kind of thing happened with a local spin. Destructive overharvesting, and then not returning the shells and instead using them for other things that damaged the coastline.

BLITCH: Much of the harvest of oysters in this state back in the early 1900s wasn’t actually for consumption. It was roadbed material, essentially.

GRABER: And to make it even worse, those road beds were built so that giant logging trucks could get into the marsh and haul out massive cypress trees that stabilized the marshes.

BLITCH: It’s not easy to drag anything out of a swamp, especially a giant tree. And so, oysters and other shellfish that they found in places like Lake Pontchartrain and, and, you know, made it Terrebone and all these other places near shore. Were converted to roadbed material.

GRABER: And then there’s another vicious cycle happening: once you destroy the reefs, the muddy water moves more slowly. It’s no longer being sped up by being funneled around the reef structure.

BLITCH: And when water moves more slowly, the sediment that it carries actually can fall out of suspension and bury a reef. That’s happened.

TWILLEY: What all of this means is that if you fast forward a couple of centuries, those enormous oyster reefs of old? They’ve disappeared. In some places like New York they’re gone, more or less completely. In others, like Louisiana, they were only partially destroyed. But globally, scientists say we’ve lost a full 85 percent of our oyster reefs.

GRABER: You might think that the loss of reefs was the reason we stopped eating oysters. I mean, who really is eating 600 oysters a year these days?

TWILLEY: Hashtag goals.

GRABER: But that’s not quite the order things happened. What actually happened is that there was a time when eating an oyster was like playing Russian roulette.

TWILLEY: Because of urbanization. Let’s take New York City as an example. In the 1800s, New York City grew dramatically. The population went from 60,000 people in 1800 to nearly three and a half million a century later, in 1900. Which is quite a jump. And all those New Yorkers used the toilet frequently.

GREENBERG: You know, there’s an old, Yiddish expression which translates as, “don’t shit where you eat.” And that is exactly what New Yorkers did.

GRABER: Because all those toilets were basically flowing directly into the harbor. By the early 1900s there was about 600 million gallons of raw sewage flowing out every day.

GREENBERG: Just a huge amount of just, feces going into the water.

TWILLEY: In a sick twist, the sewage actually made oysters grow faster. Our shit is full of nutrients, after all. But as we know and people back then didn’t, there is a downside to eating oysters that have been fed on untreated human feces. Because our shit is also full of bacteria, some of which are not so beneficial.

GREENBERG: There was a shipment of oysters that went to Chicago, and a prominent politician ate some and promptly died. And they traced the oysters back to Jamaica Bay. And, that was the last oyster ground that got closed once and for all. And so, ever since the 1920s, there have not been active attempts to grow edible oysters in New York City.

GRABER: There were still some reefs left in the harbor, but once nobody was eating oysters, people also pretty much stopped caring about the water in general. And so there was no reason to worry about dredging the channels for boats and adding more pollution into the harbor. By the end of it all, we just killed off the last of the reefs.

GREENBERG: What happened with New York was that so many oysters were destroyed that the sort of reproductive engine of the New York Bight was hobbled and never came back to where it was.

TWILLEY: What that means is that there were no longer enough oysters to breed new oysters, and so New York Harbor became what Paul calls an oyster-free blast zone.

GRABER: The same fate befell oyster reefs all around the country, though Paul says New York City was probably the worst.

GREENBERG: San Francisco would have had an oyster fishery on Olympia oysters, and that certainly was a blast zone. The Chesapeake lost a great deal of oysters. Washington DC would have had oysters. So similar kinds of losses have gone on.

GRABER: The situation wasn’t quite as intense in Louisiana. New Orleans was a much smaller city. They didn’t eat all the oysters off all the reefs, and also the pollution wasn’t as big a problem. So there are still some wild reefs in and around the Louisiana coastline. Not like there were in the past, of course, but there are some.

TWILLEY: Nonetheless, the health and wellbeing of the American oyster reef went downhill steeply. Which was a major bummer for oysters. But initially humans weren’t that upset. We adapted to the lack of wild oysters on our coastlines by just kind of ditching them. Oysters went from one of the most popular proteins in America to falling off the menu almost altogether. By the 1960s, most Americans didn’t eat any oysters at all.

GREENBERG: I think people of my age anyway—I’m 56, would have grown up not really necessarily having an oyster cross their transom. Unless they were kind of an aficionado to some degree. So I think it kind of fell out of the mainstream, to a very, very large degree.

TWILLEY: In the Gulf, where, like we said, wild reefs hadn’t been completely destroyed, oysters were still part of the food culture.

GRABER: But overall, Paul says that by the 1970s, American commercial oyster production was just one percent of what it had been at its peak in 1910. It nearly vanished entirely.

TWILLEY: That has recently changed. Oysters have become trendy again. But these days, the oysters we eat are almost all farmed. They aren’t growing wild on reefs. Because that whole thriving habitat and ecosystem is gone. Almost.

GRABER: One place you actually can still eat a wild oyster is in the Gulf. People in the region have a tradition of harvesting reefs, but they also add back broken oyster shells called culch to those reefs to help replenish them. Commercial fishermen started doing this in about the 1920s.

TWILLEY: And actually, it was in the Gulf where people first started to think about how they could rebuild lost oyster reefs from scratch. The first attempts were in the 1960s. They used car tires, just dropped in the water. And, weirdly, the oysters seemed to like them.

GRABER: These early attempts were pretty scattered. But then things really got going around the 90s. And in the past few decades, most states that lost oyster reefs have projects to try to rebuild them—all together today there are more than 1000 artificial oyster reefs around the US.

TWILLEY: And the vast majority of these are in the Gulf. So we went to see one. That story, after the break.

[BREAK]

[ENGINE STARTING UP]

JOE MATTHEWS: So we’re in the ship channel. And they keep it deep because they’re full size ocean going ships that run up to the industries up there.

GRABER: Joe Matthews is a retired oil guy, and he now drives his fishing boat around to help out the Nature Conservancy. He took us out one sunny morning and we headed out west of New Orleans. We motored out past large ships and a natural gas plant, over to an oyster reef that the Nature Conservancy built. Then we slowed down.

[ENGINE, WATER RIPPLING]

GRABER: Oh, we’re really shallow.

MATTHEWS: Yeah, yeah, we do have a low tide. We’ll try to ease up there as close as we can.

GRABER: It’s only a foot and a half of water below.

TWILLEY: The water was crystal clear at this point as well as really shallow, and we could not only see the reef, we could see actual oysters growing on it!

GRABER: Does make you hungry, huh?

[LAUGHTER]

TWILLEY: I would love an oyster.

GRABER: We didn’t get out of the boat to do any harvesting. But Joe told us that the artificial reef is not only growing oysters, which is amazing, but it’s also doing another one of its jobs and building a new habitat.

MATTHEWS: I’ve been out here and it’s just been so cool because you can see a redfish come swimming up on top of the gabion. Just looking around, kind of thing. And then like a, a black drum or a sheep head will have tail up. And it’s chomping on the little barnacles and stuff on top of the gabion.

TWILLEY: The gabion that Joe is referring to is basically a wire cage, like a big cube, filled with rocks.

BLITCH: It’s completely inert. It doesn’t look anything like a reef. But it is the substrate upon which oyster larvae will settle and grow and reproduce.

GRABER: Seth said the lumps of rock inside these cages aren’t anything special.

BLITCH: It’s lime rock. It’s gray and kind of dusty. We use the size that it’s about—on average inch and a half, two inches long. So it’s it’s the mesh of the cages is an inch and a half, so we try to use something that’s that big and a little bit bigger. So that doesn’t come out of the cages. I mean, the cages eventually will rust away which is by design. And that’s it. It’s a simple—the, each unit it’s modular, so each unit is six foot by six foot by one foot tall. And I know one foot doesn’t seem like very much. But again, you know, it’s shallow there, and so at a very low tide, the tops of the reefs will be exposed. But most of the time they’re underwater.

GRABER: From the boat, we could not only see the top of the reef, but we could also see the shoreline. It was really only a few feet away. We could even see a road that runs along the coast.

MATTHEWS: This, you see those power lines right there? That’s Highway 27. So this is kind of protecting, helping to protect any erosion toward the highway.

BLITCH: That is the hurricane evacuation route. There is no other. And so protecting that marsh ultimately protects that infrastructure.

TWILLEY: This is part of why Seth and the Nature Conservancy picked this particular spot. But of course they also had to make sure it was a place that oysters would like. One clue was that there were some pretty healthy existing wild reefs nearby.

BLITCH: We work pretty closely with the Louisiana department of wildlife and fisheries and their biologists there. And they said, yep, you know, the landing records here from the commercial harvest are good. We feel good about it. And we talked to others, and we really felt like that was a site where we would have a good chance of success.

GRABER: Seth and his colleagues spend time getting that part right because it’s work to build a reef. You can’t just head out on Joe’s boat and dump rocks overboard. The Nature Conservancy builds up thousands of tons of these rock-filled wire structures, and then the blocks get loaded onto trucks and shipped out to the water’s edge.

TWILLEY: Joe told us they were loaded onto a special airboat with a crane on it to get to the actual site, and then the crane swung them into the water.

MATTHEWS: And a couple, three people in the water and waders. You know, a crane comes in and they position it and set it down and that’s it. And on to the next one.

TWILLEY: The first gabions went in the water in 2017. And not long afterward, Seth came out to check on his baby reef and spotted the very first oyster growing on it. He remembers that moment vividly.

BLITCH: I kind of do actually, cause I took a bunch of pictures of it and send it back to the project manager. And pretty much anyone I had a phone number for. It was really gratifying to get out there and, and reach down—slowly and carefully—and feel some oysters and then be able to pull some of that rock out of those, those baskets and go, wow, there’s like four oysters on here, you know. And have them all be, you know, maybe a quarter of an inch big. Yeah, that was a really exciting day.

GRABER: All together, the Nature Conservancy has built about two and a half miles of reef out there, and they’re in the process of getting a contractor to build another mile and a half this coming summer.

TWILLEY: It’s a big project. And the good news is that the earliest chunks of reef have already survived a few hurricanes.

MATTHEWS: Yeah, Hurricane Laura. And then right after it, Delta. Laura was just… went straight up the ship channel, basically. And had 160 mile an hour winds. It was horrible. And that was three years ago, three summers ago. And it’s recovered.

GRABER: Seth told us that even before that, Hurricane Harvey dumped a bunch of rain and caused a lot of freshwater flooding.

BLITCH: It got super fresh for a really long time. And there was a lot of mortality. But again, because the structure was there, the next spawn cycle, once the salinities returned to a better place, you know, the structures were able to be a home to accommodate more oysters. And so they grew and they did really well. And we have seen really good growth of oysters, such that you can hardly see the structures we put out.

TWILLEY: Which is awesome, but it does make me wonder. Why use these lime rock and wire cages at all? Why not just put down oyster shells? That’s what baby oysters like the most. Surely that’s what would make the most sense?

BLITCH: I mean, ideally I’d like to use shell. Because oysters like to grow on other oysters, but getting shell is, is, is nearly impossible. And getting shell in the volume that we use out there—when we use thousands of tons of material. Is, is impossible.

GRABER: This is a problem that Darrah is trying to help solve. She manages the oyster shell recycling program with the Coalition to Restore Coastal Louisiana.

BACH: We are standing on an incredible pile of oyster shells. They’re everywhere as far as the eye can see. They’re piled up on each other. You can see the shells that were dumped today and shells that were dumped many months ago. What we’re standing on right now it, really looks like rock. There’s no butter. There’s no garlic. They’re totally clean now.

TWILLEY: Truly, we were standing on like a sports field full of oyster shells. Where we were the shells were about a foot deep, but over on the far edge there were bigger mounds.

GRABER: We also were really close to the water—the CRCL site is next to a canal called the Violet Canal and that connects the Gulf to some of the region’s many wetlands.

BACH: It’s a beautiful site. Out here there’s lots of birds, there’s fish in the canal, sometimes alligators, and there’s oyster shells.

TWILLEY: The shells have mostly come from restaurants, although Darrah’s nonprofit also has a couple of public drop-off bins for people who shuck and eat oysters at home. But the CRCL is partnered with more than 30 New Orleans restaurants and they’re hoping to expand

BACH: Our restaurant partners are fantastic. They’re really loyal. We find that, once they join the program, there’s no getting rid of them. They’re really into it. It’s, it becomes a big part of their brand and their image and they’re really proud of it and sharing it with their customers.

GRABER: It’s not a complicated process. The restaurants help by creating an internal flow where the oysters are separated out from the rest of the kitchen trash. Those oysters get picked up, and they’re brought to a site like this one and dumped out in a pile.

BACH: We don’t wash them. Mother Nature does that herself. But we do turn them every other month with a Bobcat to make sure that all the shells underneath our feet get exposed to the elements.

TWILLEY: This process is called curing and it helps clean the shells. It’s really a precaution just to make sure the shells are totally free of any contamination before they go back in the water.

GRABER: And as the wind and the sun and the rain are decomposing things like garlic and butter and leftover oyster bits, it does get a little stinky.

BACH: I think we got lucky with the wind today. Some days it’s pretty bad and some days you can’t smell it at all. So I think today we just got lucky. But sure, you’ll certainly smell the oysters once in a while. Some people say it makes them hungry. I don’t know if I agree with that. [LAUGH]

GRABER: I can say that the slight tang of rotting oyster did not make me hungry.

TWILLEY: Me either, thought normally anything oyster related does. But the smell wasn’t too bad, which is good because CRCL’s process actually involves having a lot of volunteers come work at the site, putting all the shells in bags. When we visited there were a bunch of shell-packed bags stacked into a wall.

[CLINKING SHELLS]

GRABER: We walked over to check them out. Each bag was made of aquaculture grade mesh and held about 30 pounds of shells.

BACH: We’re, we’re about six months out from our next reef build, so we have accumulated almost all the shells that we need bagged up for our next project.

GRABER: These bags of shells are the building blocks of the reefs. They’re basically the same thing as the wire cages of rocks that the Nature Conservancy uses.

TWILLEY: Darrah’s nonprofit, the Coalition to Restore Coastal Louisiana, has been collecting and recycling oyster shells since 2014. And so far they’ve built 5 reefs.

BACH: We’ve recycled over 13 million pounds of oyster shells from hungry people in the New Orleans area. And we have built around 8,000 linear feet of shoreline.

GRABER: Right now, Darrah and her colleagues think they’re collecting about half of remaining shells from oysters eaten at restaurants and bars around New Orleans, but they want to build more reefs. And for that to work, they need more oyster shells.

TWILLEY: Luckily the state is on board, recently the government has come up with a new incentive to encourage restaurants to get with the program.

BACH: It’s a tax credit for restaurants recycling oyster shells to earn one dollar for every fifty pounds recycled. And we’re really excited for that to take hold this year, and for restaurants all over Louisiana to benefit.

TWILLEY: Sometimes you need a carrot to get an oyster shell, what can I say. But Seth told us that even if every single shell in New Orleans was recycled and turned into a reef, there still wouldn’t be enough to restore all the reefs.

GRABER: A lot of oysters are shipped out of New Orleans, and even out of Louisiana. And also, historically there were just dramatically more oyster shells and larger reefs, so it’ll take more than all of today’s oyster shells to build them back. That’s why Seth uses rock.

TWILLEY: And either way, it works. Which is the point. First of all, both Darrah and Seth’s reefs have oysters on them.

BACH: We’re really, really fortunate to have seen oysters growing on all of the reefs that we’ve built.

BLITCH: Just, I mean, anecdotally, and just looking at them, there are hundreds of thousands to millions of oysters out there that weren’t there before. That’s a big deal. You know, that’s a, that’s a, that’s a, that’s a great outcome.

BACH: We’ve also seen, just from visiting the reefs annually, that there’s, you know, healthy marsh growing, birds landing on the reefs, and all that good stuff.

BLITCH: We have anglers that are, you know, catching, you know, sport fish, like red drum and, and sheep’s head and spotted sea trout.

GRABER: So far so good, but they’ve also studied all of this scientifically.

BACH: We do biological monitoring of each reef for five years post construction. And that looks like, our team hiring a boat captain, taking a trip out to the reef and pulling up a sample of the recycled shells that we put out there. And counting all the living and dead organisms in the sample to—draw metrics about the success of the reef developing a suitable habitat for oysters, mussels, clams, and anything else that, that ends up in the sample.

TWILLEY: And these census results are super positive. Which means that the reefs are definitely creating habitat, both for oysters and for other creatures. And the oysters are filtering water, because that’s what oysters do. But what about reducing erosion? And saving Louisiana’s disappearing coastline? Do the reefs actually work for that?

BLITCH: Sure. So we have looked at the shoreline, you know, using GPS, mapping it out and, and looking at where it is, you know, across space and time. And, and that’s a way you can measure rate of loss. And so, you know, we can look at that and know that we’re seeing a slower rate of loss than we had before the project was there.

GRABER: Darrah said they’re seeing the same thing, the reefs are having a big impact.

BACH: We’ve found from looking at our first project and looking at satellite imagery and drone imagery that over years, there was a 50 percent reduction in the rate of erosion of the reef site compared to a control site.

TWILLEY: That sounds awesome, and it is. But we were left wondering: is it worth it? After all, like Darrah says, it’s not stopping erosion. It’s just slowing it. And it’s not like building a reef is free.

BLITCH: [LAUGHS] It’s not cheap and it depends on the kind of material and it depends on whether it’s tidal or sub tidal. It depends on a lot of things. But our work, when I first got here, the figure we were thrown around was it was about a million dollars a mile, to put out a project. And that was everything. That was the permitting. That was our time. That was the material cost and the contract costs. And, and a little bit of monitoring that happens. These days, it’s more like, you know, 1. 3 to 1. 5 million a mile.

GRABER: Darrah’s is a little less expensive because they don’t have to buy material and they use a lot of volunteers to put it together. But still there is a cost.

TWILLEY: To be fair, the other options on the table—the ones we told you about at the start, like the big projects to re-re-engineer the river and divert that sediment into the disappearing wetlands—those kinds of projects have price tags in the billions, not the millions.

GRABER: But even though the cost of these sediment diversion projects is mind boggling, Seth and Darah both say they’re essential.

BACH: And it’s been the position of CRCL since it was founded that if we don’t reconnect the river to the wetlands, the projects that are being done in the wetlands themselves will, over time, fail.

GRABER: Because like we said, reefs just slow erosion down. And so if there’s no replenishment of sediment and mud, the coasts will still disappear, just more slowly.

TWILLEY: So oyster reefs can never save the coastline on their own. But Seth and Darrah agree that they are *also* an important part of the solution.

GRABER: For one, they kind of take care of themselves. The other projects, even once you build them, you have to keep pouring money into them to maintain them. But the reefs aren’t like that.

BLITCH: Once your initial expense is done, oysters do all the work for free. They filter the water for free. They protect the shoreline for free. They create habitat for free once they’re there. And so that’s kind of cool. And you know, and you can’t do that with any other project.

GRABER: And oyster reefs have another benefit that’s harder to quantify, but it’s also important—they help connect people back to the water. And once people feel connected, they care, and they’re more likely to try to protect it.

BACH: For us, the projects that we build are so impactful for the volunteers that work on them and the communities that work with us. That’s the biggest success story that we could hope for and that really gives us faith in our projects.

TWILLEY: Oyster reefs are obviously a feel-good solution—what’s not to love? But they are also a real solution. Seth told us a story about an island in the Louisiana wetlands called Rabbit Island. It was disappearing like everything else.

BLITCH: A lot of nesting seabirds out there. And as the island started to erode away, it just made less and less space for those birds to nest and raise young. And so that hurts populations.

GRABER: To save the island and the birds, the state spent a lot of money pumping a lot of sediment onto the island to keep it from eroding away entirely.

BLITCH: But almost as immediately, you know, it started to erode again.

TWILLEY: And so the state borrowed a trick from the Nature Conservancy

BLITCH: And they built a reef there, to protect that island, to preserve the bird populations and also grow oysters.

GRABER: And the combo of the two worked.

BLITCH: So they’re, you know, as a habitat, oysters are critically important to coastlines. There’s no panacea, you know, solving the oyster problem isn’t the silver bullet to Louisiana’s coastal woes, but it is definitely part of the picture.

TWILLEY: The Gulf was first to get on the oyster reef restoration train, but like we said, today, people everywhere are rebuilding lost reefs.

BLITCH: I think I could think of a project in almost every coastal state in the country, especially in the Gulf and Atlantic sides. We’re seeing it everywhere. There’s certainly a need everywhere.

GRABER: One of those places where there are new reefs going in the water is in New York’s harbor, which as we described had reefs that were totally wiped out. We’ll tell the story of how New York’s new baby reefs are doing in our special supporters’ newsletter, gastropod.com/support.

TWILLEY: Saving the world or at least the coastline and all its biodiversity is great. But what’s also great is eating oysters. And all this talk of oysters and oyster reefs is making me really hungry, even after breathing in the sweet aroma of Darrah’s pile. So can we eat the oysters from these new reefs?

GRABER: In theory, sure, the water is clean enough and the oysters won’t make you sick. Some of these artificial reefs are being harvested, but Darrah’s and Seth’s aren’t. The goal is restoration and creating an oyster sanctuary. Seth admits he could have taken an oyster knife out and at least tried one—

BLITCH: I, I don’t know if it’s paternal instinct or what, but I. I’ve gone out to the reef and then gone to a restaurant, eating lots of oysters, but I haven’t eaten any off our reefs.

TWILLEY: That said, when Seth’s oysters spawn, they help repopulate nearby wild reefs that are harvested, so yay, more oysters for dinner. Which is a really delicious thing and a really good thing.

GRABER: A lot of the oysters most of us eat these days are grown in cages, which is how most oyster farming is done. But these are great too! They help clean the water and then other things like eelgrass can grow and provide habitat for other fish. As Paul says, whatever kind of oyster you eat, it’s all awesome!

GREENBERG: Buying an oyster, it’s a transaction with clean water, that actually drives more clean water. So I would say yes, let’s eat some more oysters.

[MUSIC]

TWILLEY: We agree 100 percent. Thanks this episode to Paul Greenberg, Seth Blitch, Darrah Fox Bach, Boyce Upholt, and Joe Matthews. We have links to Paul and Boyce’s books and Seth and Darrah’s organizations on our website, gastropod.com.

GRABER: Happy birthday to Gastropod super supporters Zenna & Keoni. Thanks also to our fabulous producer and fellow oyster lover Claudia Geib. We’ll be back in a couple of weeks with a brand new episode, ‘til then!