Oyster

• 1. Introduction

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  An oyster has no brain. Under its adductor muscle sits a small, three-chambered heart that pumps colorless blood, flanked by two kidneys and a scattering of nerve cords. Yet this brainless filter feeder built fortunes, fed cities, and now stands as a candidate to clean polluted bays and blunt rising seas. Jonathan Swift is quoted as having said, "He was a bold man that first ate an oyster." Boldness aside, humans have eaten them since prehistory. Some middens in New South Wales, Australia, are dated at ten thousand years. So what exactly is an oyster, given that the word covers several unrelated families of bivalve mollusc? How did a working-class food in early 19th-century New York become an expensive delicacy? And why are scientists building artificial reefs to bring it back? The answers run from Roman hydraulics to the Chesapeake Bay, from pearls the size of dinner plates to a knife with a blade about 5 cm long.

• 2. Many Families, One Name

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  True oysters belong to the family Ostreidae, the group that includes the edible kinds in the genera Ostrea, Crassostrea, Magallana, and Saccostrea. Among them are the European flat oyster, eastern oyster, Olympia oyster, Pacific oyster, and the Sydney rock oyster. Ostreidae evolved in the Early Triassic epoch, when the genus Liostrea grew directly on the shells of living ammonoids.

  Pearl oysters are not close relatives at all. They belong to a distinct family, the feathered oysters or Pteriidae, even though almost any shell-bearing mollusk can secrete a pearl. The largest pearl-bearing oyster is the marine Pinctada maxima, roughly the size of a dinner plate, and not every individual produces a pearl. In nature, the animal covers a minute invasive object with layer upon layer of nacre until an irritant becomes a gem; its color and shape depend on the nacre's natural pigment and the original irritant's form.

  The word oyster carries its own lineage. It comes from Old French oistre and first appeared in English during the 14th century, traced back through the Latin ostrea to the Ancient Greek ostreon, a word to compare with osteon, meaning bone. Other bivalves borrow the name through resemblance rather than kinship: thorny oysters in the genus Spondylus, the pilgrim oyster that is really a scallop, the saddle oysters of the Anomiidae also called jingle shells, and the translucent windowpane oysters harvested for their shells. In the Philippines, a local thorny oyster called Tikod amo commands high prices in the south for its good flavor.

• 3. A Body Built To Filter

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  Oysters breathe primarily through their gills, but they also exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. Their nervous system runs on two pairs of nerve cords and three pairs of ganglia, with no evidence of a brain anywhere in the animal. Some species carry two sexes, like the European oyster and the Olympia oyster, yet their reproductive organs hold both eggs and sperm, so an oyster can technically fertilize its own eggs.

  Filtering is the work that defines the creature. Beating cilia draw water in over the gills, where suspended plankton and stray particles get trapped in mucus and carried to the mouth, then expelled as feces or pseudofeces that sink out of the water column. They feed most actively between 68 and 78 degrees Fahrenheit. Under ideal laboratory conditions, a single oyster can filter up to 50 US gallons of water per day, though mature animals under average conditions manage 3 to 12 US gallons.

  The scale of that filtering once reshaped an entire estuary. Chesapeake Bay's flourishing oyster population historically strained excess nutrients from the estuary's entire water volume every three to four days. By 2008, with the population collapsed, the same complete cycle was estimated to take nearly a year.

• 4. Reefs And Rhythms

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  A group of oysters is called a bed or an oyster reef, and the animals living in it keep strict time. Their behaviour follows circatidal and circadian rhythms tied to the relative positions of the moon and sun. During neap tides, when shifts are mild, they hold their valves closed far longer than during the more drastic spring tides. Even permanently submerged, they shut to enter a resting state.

  The reef is a city for other animals. Its hard shell surfaces and the nooks between shells shelter hundreds of species, including sea anemones, barnacles, and hooked mussels, which in turn feed striped bass, black drum, and croakers. An oyster reef can multiply the surface area of a flat bottom tenfold. A mature oyster's shape depends on the bottom it first attached to, but it always tilts its outer, flared shell upward, with one valve cupped and the other flat.

  Reproduction follows a sequence of sexes across years. Oysters are protandric: in their first year they spawn as males, releasing sperm, then over the next two or three years they spawn as females, releasing eggs. Bay oysters usually spawn from the end of June until mid-August, when a rise in water temperature prompts a few to release and triggers the rest, clouding the water. A single female can produce up to 100 million eggs annually. The fertilized eggs become larvae that settle on a surface such as another oyster's shell, where the attached young, called spat, measure less than 25 mm long.

• 5. Empire Of The Beds

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  Sergius Orata of the Roman Republic is considered the first major merchant and cultivator of oysters. Using his knowledge of hydraulics, he built channels and locks to control the tides, and the Romans joked that he could breed oysters on the roof of his house. The French seaside resort of Cancale in Brittany has grown them since Roman times, as has the English town of Whitstable, noted for beds on the Kentish Flats used since the Romans. The borough of Colchester still holds an annual Oyster Feast each October, where "Colchester Natives," the native Ostrea edulis, are eaten.

  New York Harbor turned the oyster into an industry. Through the 19th century its beds became the largest source of oysters worldwide, and on any given day in the late 1800s six million oysters could be found on barges along the city's waterfront. They were cheap, eaten mainly by the working class, and they helped launch the city's restaurant trade while employing hundreds. Rising demand exhausted the beds, foreign species brought disease, and effluent and sedimentation from erosion destroyed most of them by the early 20th century. Scarcity raised prices and converted a working-class staple into an expensive delicacy.

  The drink trade made its own claim on the shell. In Victorian England it was common to pair a favorite beer with oysters, and people found that rich, sweet, malty stouts suited the briny, creamy meat. Brewers then discovered that oyster shells naturally clarify a beer and began adding crushed shells to their brews. The first known brewery to do so was in 1938 at the Hammerton Brewery in London, where the oyster stout began.

• 6. Harvest And Husbandry

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  Oyster tongs reach the beds that hands cannot. In shallow water gatherers use small rakes; in deeper water long-handled rakes or tongs, and patent tongs lowered on a line reach beds too deep to touch directly. A scallop dredge, a toothed bar attached to a chain bag, works faster but heavily damages the beds, so its use is highly restricted. Until 1965, Maryland limited dredging to sailboats, which prompted the development of specialized craft, the bugeye and later the skipjack. Connecticut passed similar sail-only laws before World War I that lasted until 1969, and Hope, completed in 1948, is believed to be the last-built Connecticut oyster sloop.

  Cultivation predates these regulations by millennia, reaching back at least to the Roman Empire. The Pacific oyster, Magallana gigas, is now the most widely grown bivalve in the world. Growers raise spat onshore, then either release it across existing beds to mature like wild stock, or keep it in racks or bags above the bottom, a costlier method that shields the animals from some predators. Some farmers grow Pacific oysters in the outflow of mariculture ponds, where the roughly 9 kg of feed wasted for every 1 kg of fish or prawn becomes food for the phytoplankton the oysters eat.

  Growers can also stop oysters from breeding entirely. By crossbreeding tetraploid and diploid oysters, they produce sterile triploids that cannot propagate, which keeps introduced animals from spreading into unwanted habitats. The technique matters because introductions carry risk: the eastern oyster reached California waters in 1875 and the Pacific oyster in 1929, and the Pacific oyster eventually spread up and down the coast from Pendrell Sound to become the basis of the North American west coast industry.

• 7. Reefs As Infrastructure

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  Individual oysters can filter up to 190 liters of water a day, pulling nitrates, ammonia, phosphates, plankton, detritus, bacteria, and dissolved organic matter out of the column. In Maryland, the Chesapeake Bay Program set out to use oysters to cut nitrogen entering the bay by 8600 metric tons per year by 2010. By one estimate, a single acre can produce nearly 750,000 oysters filtering between 57,000 and 150,000 cubic meters of water daily.

  The "oyster-tecture" movement turns that capacity into shoreline defense and water purification. At Withers Swash in South Carolina, a project led by Neil Chambers-led volunteers filters roughly 4.8 million liters of water daily for an installation cost of $3000. In New Jersey, the Department of Environmental Protection refused to allow oysters as a filter in Sandy Hook Bay and the Raritan Bay, fearing risk to commercial growers and that people might eat tainted oysters, so New Jersey Baykeepers partnered with Naval Weapons Station Earle, whose 24/7 security blocks poaching.

  Recycling the shells closes the loop. Non-profits collect shells from restaurants, wash and dry them, and set them in the sun for up to a year to kill bacteria before returning them to the water. The Billion Oyster Project in New York aims to engage one million people to return a billion oysters to the harbor, working with more than 60 restaurants. The NOAA Office of Habitat Conservation awarded $5 million to Restore America's Estuaries to rebuild reefs in Louisiana, Florida, Alabama, and Texas. Near the mouth of the Great Wicomico River, five-year-old artificial reefs now harbor more than 180 million native Crassostrea virginica, raised in part by elevating the reef floor 25 to 45 cm with waste shell.

• 8. On The Plate

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  Raw oysters carry complex flavors that shift by variety and region: salty, briny, buttery, metallic, or fruity, with a soft and fleshy texture. North American varieties include Kumamoto and Yaquina Bay from Oregon, Duxbury and Wellfleet from Massachusetts, Malpeque from Prince Edward Island, Blue Point from Long Island, Pemaquid from Maine, and Cape May from New Jersey. They can be eaten raw, smoked, boiled, baked, fried, roasted, stewed, pickled, or in the elaborate Oysters Rockefeller, and upscale restaurants pair the raw kind with a mignonette of shallot, mixed peppercorn, dry white wine, and lemon juice or sherry vinegar.

  The meat is lean but dense in nutrients. One dozen raw oysters provides only 110 kcal, while 100 g of Pacific oysters delivers about 9 g of protein. Just two oysters, 28 g, supply the Reference Daily Intake of zinc and vitamin B12, and the animal is also rich in iron, calcium, selenium, and vitamin A. A team of American and Italian researchers found bivalves rich in amino acids that raise sex hormone levels, lending some basis to the old reputation as an aphrodisiac.

  Safety has always shadowed the pleasure. The folk rule that oysters are safe only in months with the letter 'r' holds a kernel of truth, since in the Northern Hemisphere they spoil more readily in May, June, July, and August. As filter feeders they concentrate whatever is in the water, including Vibrio vulnificus, the most deadly seafood-borne pathogen, most dangerous to immunocompromised people. To open one, Zora Neale Hurston's chosen weapon was the oyster knife; she wrote, "No, I do not weep at the world--I am too busy sharpening my oyster knife." Professional shuckers slip that short blade into the hinge and cut the adductor muscle in fewer than three seconds, a speed now tested at competitions like the championship held at the Galway International Oyster Festival in Ireland.