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Behold the many wonders of the oyster, the sex-crazed champion of the sea

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Oysters seem like very simple animals: just two rocky shells surrounding globs of gray flesh.

But this modest appearance belies the oyster's extraordinary capabilities, which range from filtering water to reengineering coastlines to restoring destroyed habitats for North American marine life.

Oysters helped form the planet as we know it today. "Basically, they make rock," as their shells become the basis for limestone, Rowan Jacobsen, the author of A Geography of Oysters, writes me in an email. "They make the condos of the sea, where all the little creatures and juvenile fish find shelter."

What's also true is that there used to be a lot more of them in the ocean. Wild oysters used to dominate New York Harbor and the Chesapeake. According to the New York Public Library, "Some biologists estimate that the New York Harbor contained half of the world’s oysters." In the Chesapeake, oyster reefs were so prominent they were a hazard to ships sailing the waters.

Overfishing, pollution, and disease all but wiped them out in New York. And in the Chesapeake, the wild oyster population is down to 1 percent of its historic levels.

NOAA

But there's also lots of good news: because they can improve marine ecology, restoration projects are underway in each waterway. And there's big momentum in the US oyster farming industry, which is one of the main contributors of the growth in US aquaculture, the National Oceanic and Atmospheric Administration reports.

Rowan Jacobsen is just one of the oyster's many boosters. Others include Pete Malinowski of the Billion Oyster Project, an initiative to restore live oysters to New York Harbor, and Stan Allen, a researcher at the Virginia Institute of Marine Science who has studied oyster cultivation for 35 years. They walked me through the many wonders of the oyster.

Here's what to know.

1) Oysters live two lives

The wonder of the oyster begins with its birth. Although we usually think of oysters as being immobile rocks, they start off their lives being able to swim through the water.

Oyster embryo.
National Science Foundation

"If you look at a baby oyster in its swimming stage, it actually looks like a tiny clam that swims around," Allen says.

Within 12 hours of their birth, they start to form shells, pulling calcium out of the water and depositing it as calcium carbonate on the outside of their bodies. Little bit by little bit, the shell grows. About three weeks after birth, there comes a point where the animal grows heavy and seeks to settle down.

Swimming oyster larvae.
Via Youtube

"It wants to settle down to attach to some substrate, something hard where it can make its living for the rest of its natural life," Allen explains. In the wild, oysters will settle down upon other oysters, creating vast reefs that then provide shelter and an environment for other animals. Oyster farmers, meanwhile, simulate this by offering structures for oysters to attach to or by planting baby oysters on existing beds.

2) Oysters are sex-crazed horndogs

Via Getty Images

Life isn't easy for a tiny baby oyster.

Because they are so small and defenseless without a fully formed shell, oyster babies are often gobbled up by other marine life.

To ensure the survival of their species, oysters respond to this threat by ejaculating ungodly numbers of sperm and eggs into the water (where the gametes mix and form oyster embryos).

Every season, an adult female oyster can produce 50 to 100 million eggs. Males produce so much sperm that it's basically uncountable. "Sperm counts ... certainly range into the tens of billions," Allen says. "They are maybe the most fecund of species on the planet."

Now consider this: An oyster reef can house around 100 to 500 oysters per 10 square feet. An acre of a healthy oyster reef can house 600,000 of them, and some oyster reefs can stretch hundreds of acres. Let's just say there aren't enough digits on a standard calculator to determine how much oyster sperm that is.

3) Oysters can change gender multiple times throughout their lives

Almost all oysters start out their lives as male, but as they grow larger, many of them will switch genders. (Because there's so much more sperm than eggs, this helps ensure a growing oyster population.)

And occasionally they can have both sex organs at the same time. Allen says how this happens isn't well-understood, but they seem to change genders based on environmental factors. It's possible that the gender determination is influenced by water temperature and by the relative health of the oyster reef (more productive reefs favor females). But "nobody really knows what the mechanism is," Allen says.

4) Oysters create their own ecosystems

In the 1600s, when Henry Hudson first navigated the New York waters, there were an estimated 220,000 acres of oysters in New York Harbor, according to the Billion Oyster Project website. Now, after centuries of industrialization, there are hardly any.

Which is a shame. Because when oysters settle down after their swimming phase, they prefer to attach themselves to other oysters. This can create vast reef systems the can house other animals as well.

"They provide food and habitat for thousands of species of fish and invertebrates," Malinowski says. "When we put an oyster reef down, we see immediate and dramatic changes in local biodiversity in the matter of weeks."

Malinowski's team is hoping to bring back 100 of those acres of oyster reefs, to restore New York Harbor ever so slightly.

Reefs can act as breakwaters, deadening the force of ocean waves before they reach the shore. According to NOAA, oyster reefs can "significantly [reduce] the energy of high power waves by as much as 76 to 93 percent, which, in turn, lessens the amount of coastal erosion, flooding, and costly damage to private property and public infrastructure." That would have been helpful to dampen the storm surge during Hurricane Sandy in 2012.

Restoring a reef means putting down metal cages or other hard surfaces that oysters can attach to. It's like starting a rubber band ball with a marble: The oysters need an initial hard surface to attach to, but once they start growing, they can transform the artificial reef into a natural one.

An artificial oyster reef.
US Fish and Wildlife Service

5) Oysters filter the water

One of the main perks of restoring oyster reefs is that you'll also get cleaner water.

Because oysters don't move much, they have to eat whatever floats by. "All of the good food gets passed into the digestive system, and everything that’s not food gets wrapped up in mucus and gets rejected out of their shell," Malinowski says. The rejected material is wrapped in a mucus called pseudofeces, and it plays a big role in removing dirt and plankton from the water.

Watch how quickly a bundle of oysters can clean up the water in this tank.

"It’s removing all the suspended particles, packing them up, and putting them on the bottom where they can be consumed by other animals; it’s basically creating fish pellets," Malinowski says. A single oyster can filter around 50 gallons of water a day.

What oysters clean up best is nitrogen. Wastewater from sewage treatment can contain a lot of it, and when it's released into rivers and bays, it can lead to huge blooms of algae. The algae can then deplete the water of oxygen, making it unsuitable for many forms of life. Nitrogen can also enter the environment via fertilizer runoff from farms, leaving aquatic "dead zones" depleted of oxygen in its wake. "What oysters do is they take that algae out of the water column [and] put them in the sediment," Malinowski says, which allows water to stay oxygen-rich.

One misconception is that oysters can clean up environmental toxins like mercury and plastic, Malinowski says. The oysters do remove some of those contaminants from the water, but as long as they remain in the oysters' bodies the toxins can still cycle through the ecosystem (namely, if they're eaten by other marine life.)

6) Oyster farming is pretty darn sustainable

Drakes Bay Oyster Company Marks Closing After Feds Deny Use Of Federal Lands Photo by Justin Sullivan/Getty Images

After oysters have been seeded and are growing, they don't require any additional food. "Because they're filter feeders, you're not feeding them from food source like a salmon farm would," says Allen. "You're not adding anything to the environment other than a structure upon which oysters can grow. It's a win-win." And because oyster farming is separate from oyster reef restoration, it doesn't impact the number of wild oysters that can help protect our shorelines.

Compare that with pretty much any other aquaculture or agriculture operation, which has lots of inputs and outputs. "I think of this as their killer app," Jacobsen writes. "Even vegetable farms require lots of fertilizer and water (as well as pesticides and other chemicals)."

Seafood Watch, a consumer watchdog group, reports that oyster farms can help remove unwanted nutrients from their environment. "Overall, impacts of oyster farming are likely to be minor and unlikely to reach beyond the immediate vicinity of the farm; and because benefits may outweigh such risks, there is no concern regarding resultant effluent or waste impacts."

Given that the net environmental impact of oysters may be positive while their production is humane, some even consider them to be vegan.

7) Oh, yeah, pearls are cool too

Considering all this, perhaps oysters' most famous ability is arguably its least impressive: They can make shiny stones.

So the next time you see an oyster, well, definitely eat it. But as you savor that salty, briny, unctuous glob, appreciate the little beast for all the wonders it can do.