Oysters contain multitudes: They’re protein-rich treats, highly efficient water filters, reef builders, and pretty rock-makers. They exist in coastal regions all over the world, from the Aleutian Islands of Alaska to the warm waters around New Zealand, and we’ve been eating them for thousands of years. Yet as Jonathan Swift wrote in his book Polite Company, “He was a bold man that first ate an oyster.” After all, the shellfish can be a little treacherous to open, and what’s inside isn’t everybody’s cup of tea. But how much do you really know about oysters? Do they all make pearls? Have they always been a delicacy? What can you do with the shells? Pry open these six interesting facts about some of the world’s most divisive shellfish.
Not All Pearls Are Shiny
Pearls, the semiprecious gems popular for jewelry and other adornment, are created when some kind of unwelcome object, such as a grain of sand, enters an oyster’s shell. The oyster shields itself by wrapping the irritating object in a substance called nacre, a tough material that develops inside the shells of oysters from the Aviculidae family, also known as pearl oysters. The nacre builds up into a pearl, which can be of several different colors.
Oysters cultivated for food are from the Ostreidae family, or true oysters. They create pearls when things sneak into their shells, too, but their pearls don’t have the same lustrous coating that those of pearl oysters do — so they end up just small and bland.
Oysters Can Change Sex
Many of the oysters commonly used for food, including European flat oysters, Pacific oysters, and Atlantic oysters, change sex during their lifetimes — sometimes a few times. European flat oysters alternate based on seasons and water temperature. In other species, most oysters are born male and eventually the population evens out. Most older oysters are female, but some change back at some point. The exact mechanism that makes this happen is still something of a mystery.
One Oyster Can Filter Up to 50 Gallons of Water a Day
Oysters are a critical part of marine ecosystems because they eat by filtering water, removing sediment and nitrogen in the process. One adult oyster can filter up to 50 gallons of water a day, although the exact rate depends on water conditions. A typical ocean environment has stressors, like high or low temperatures, predators, and especially dirty water, that can slow down their feeding process. In more typical conditions, an oyster filters 3 to 12.5 gallons of water a day, which is still extraordinarily helpful.
All this water filtration does have a couple of drawbacks: Too many oysters can reduce the nutrients in the water for other animals, and because they take in a lot of junk, they can pass toxins onto us when we eat them.
Oyster Shells Are Recyclable
Don’t throw away your oyster shells when you’re done shucking — they’re the best material for rebuilding oyster beds, which sometimes create giant reefs that can be home to all kinds of marine life. When oysters reproduce, they release larvae into the ocean, which float around looking for somewhere to attach themselves. With the loss of reef habitats, those spots can be harder to find. Those larvae love to cling to old oyster shells, which makes discarded shells one of the best tools for sustainable oyster farming and rebuilding marine ecosystems — something they certainly can’t do in a landfill. Many municipalities and conservation groups in oyster-rich areas offer some kind of recycling program.
Humans Have Been Cultivating Oysters for Thousands of Years
Oyster farms, particularly sustainable oyster farms, are nothing new. A 2022 archaeological study in the United States and Australia found that Indigenous groups cultivated oyster reefs as far back as 6,000 years ago, and managed to maintain healthy oyster populations for as long as 5,000 years, even with intense harvesting.The oldest oyster middens — hills of oyster shells — were in California and Massachusetts. One midden in Florida contained more than 18 billion oyster shells.
Overharvesting has damaged modern-day oyster populations; the study also found that 85% of oyster habitats from the 19th century were gone by the 21st century.
Oysters Were Much More Popular in 19th-Century America
Oysters certainly have their fans in the 21st century, but not like they did in the 19th century. Back then, they were a staple protein because they were both abundant and extremely cheap. They were equally treasured in both fine dining establishments and on city streets. Oyster houses were incredibly common, and inspired the kind of camaraderie and revelry that bars do today — some of them sold beer with oysters as a free snack.
Their popularity wasn’t limited to coastlines; middle America couldn’t get enough of them, either. Oysters were shipped via rail even before beef was. Households would buy them by the barrel and put them in soups, sauces, and even stuffing.
So what happened to the oyster craze of yesteryear? Several things. With overharvesting, the supply wasn’t as great as it once was. Growing cities started dumping sewage into the water, and oyster beds became disease vectors. New food safety regulations — and an end to child labor — meant businessmen couldn’t get away with shady practices that made oysters cheap.
The final nail in the oyster coffin was Prohibition. Oyster bars had already mostly disappeared by then, but they lost their drinking clientele to speakeasies, and their nondrinking regulars thought they were still too much like saloons.