Oysters are slimy, yet delicious. Casanova purportedly ate 50 of them for breakfast daily—and he isn’t the only one who believed they had certain powers. Oysters are definitely key to healthy marine ecosystems and clean water. Here are 15 facts about these ugly yet amazing shellfish.

1. THEY'RE BETTER WATER FILTERS THAN BRITA BY FAR.

Every day, one oyster filters 50 gallons of water and a healthy one-acre reef around 24 million gallons—enough to fill 36 Olympic swimming pools. Here’s how that works. An oyster draws water in over its gills using cilia, or tiny hairs. Plankton and particles in the water are trapped in mucus in the gill, then transported to the oyster’s mouth. So, yeah, oysters basically eat their own snot but, at the same time, remove excess sediment, nutrients, and algae from the water. That keeps the water in good shape for other marine life.

2. THEY DEVELOP NEIGHBORHOOD COMMUNITIES.

A close-up image of a Gulf Coast oyster bed taken in 2007 for a federal ecosystem restoration initiative. Image credit: EPA via Wikipedia Commons // Public Domain 

Oysters form beds or reefs that provide important habitat for fish and other creatures, including sea anemones and barnacles, which in turn provide food for bigger fish such as striped bass, black drum, and croaker. That works out to 1.5 extra tons of seafood a year.

3. SPRING IS WHEN A YOUNG OYSTER LOOKS FOR LOVE.

Oysters spawn when water temperatures rise in spring. Females release millions of eggs and males even more sperm and some of these lucky gametes meet in the open water. Fertilized eggs develop into microscopic larvae, little more than tiny black specks, which feed on algae, drifting on currents and tides for three weeks. Then, if something else hasn’t eaten them, the larvae attach to a hard surface, most likely other oysters, and transform into a tiny oyster called a spat. In areas where reefs have declined, oyster larvae may never find a place to settle.

4. THEY HOLD BACK FIERCE WAVES. 

Oyster reefs provide an effective natural barrier to storm waves and sea level rise. They absorb as much as 76 to 93 percent of wave energy, which reduces erosion, flooding, and property damage from coastal storms. Oyster reefs are preferable to manmade rip-rap or bulkheads, which don’t provide other benefits, such as habitat, and cost a lot to maintain. According to a Mississippi-Alabama Sea Grant Consortium report, 100 miles of oyster reefs could save up to $95 million on rip-rap or $150 million on bulkheads.

5. FORGET THE 'R' POLICY—OYSTERS ARE GOOD FOR YOU YEAR-ROUND.

Oysters are high in zinc, which is good for your immune system, and also provide calcium, vitamin C, omega 3 fatty acids, iron, and protein. Jason Hedlund, seafood coordinator for Whole Foods Markets, told mental_floss that oysters are low in cholesterol as well. “And that old rule about only eating oysters in months with an ‘R’ in them no longer applies, thanks to developments in food safety,” he added. 

6. IRRITATION LEADS TO BEAUTY AND VALUE.

Not an accurate representation of how pearls are found in oysters. Image credit: iStock

Closely related to the food oysters (family Ostreidae) are the pearl oysters (family Aviculidae). When any small irritant such as a grain of sand gets inside an oyster shell, the animal covers it with nacre, or mother-of-pearl, the substance that forms the inside lining of the shell. Over several years, as more layers are added, a pearl forms. The type, color and shape of a pearl depend on pigment in the nacre and the shape of the original irritant. Today, most pearls are cultured, or created in farmed oysters. Cultured pearls look just like natural ones but are considered less valuable.

7. BAD NEWS: OYSTER REEFS ARE GREATLY IMPERILED WORLDWIDE.

Oyster reefs are the single most imperiled marine habitat on Earth, with 85 to 90 percent of wild reefs lost. The main culprit is destructive fishing practices, including overharvesting, according to a report from The Nature Conservancy, along with habitat loss and declining water quality.

8. GOOD NEWS: REEF RESTORATION WORKS.

Fortunately, oyster reef restoration efforts are very successful. Some 80 restoration projects are currently underway around the U.S., including Nature Conservancy projects in Texas, Louisiana, Mississippi, Alabama, Florida, Georgia, South Carolina, and North Carolina.  Monitoring of these projects has shown as much as 212 percent increases in oyster growth and 850 percent increases in other marine life on the reefs. NOAA is involved in oyster reef restoration in Chesapeake Bay, where native populations had plunged to 1 percent of historic levels.

A study in the Journal of Applied Ecology reviewed literature on the increase in juvenile fish and mobile crustaceans in Crassostrea virginica reefs in the US and found increased production for 19 and 12 species, respectively, in the Gulf of Mexico and in the South and Mid-Atlantic.

9. WE CAN GET CREATIVE WITH REPAIRING THEIR HOMES.  

Marsh grass and oyster beds. Image credit: Steve Hillebrand, U.S. Fish and Wildlife Service, via Wikimedia Commons // Public Domain

A variety of techniques work for oyster reef restoration, from shooting oyster shell from high-pressure hoses to placing bags of shells in the water. Some projects have built lines of shell and rock to stabilize the shoreline along with planting sea grass behind the reef to provide additional habitat. In areas without existing structure for "spat set" (a good location for young oysters, a.k.a. spat), seed oysters from hatcheries are used to establish new reefs.

10. OYSTERS DON'T HAVE FUN ON ACID.

As the oceans absorb more carbon dioxide, it changes the chemistry of the water. The world’s oceans have become 30 percent more acidic since the start of the Industrial Revolution, and that can kill oyster larvae and make it harder for oysters to form shells. 

11. HARVESTING OYSTERS THE RIGHT WAY DOESN'T HARM OTHER SPECIES.

The Monterey Bay Aquarium Seafood Watch rates Eastern oysters from Alabama, Louisiana, Mississippi, Texas, and Florida caught by dredge or tong as "Best Choices." The oyster harvest has no bycatch—other species of marine life caught along with the intended target. Seafood Watch recommendations “help you choose seafood that’s fished or farmed in ways that have less impact on the environment,” according to the organization.

12. THERE ARE FIVE SPECIES IN U.S. WATERS.

A 1910 map of public oyster beds in Virginia's James River. Image credit: Wikimedia Commons // Public Domain

Oysters are found on the East, West, and Gulf Coasts of the US. Crassostrea virginica, the Eastern oyster, ranges from Canada to Key Biscayne, Florida, and throughout the Gulf of Mexico. Ostreola conchaphila is native to the West Coast, where farmed reefs also contain the widely cultivated Pacific or Japanese oyster, Crassostrea gigas. Two more oysters are grown for specialty markets: the European Flat oysters (Ostrea edulis) and Kumamatos (Crassostrea sikamea).

13. ALL YOU NEED IS THE RIGHT KNIFE. OR BACON.

Raw, grilled, fried, wrapped in bacon, mixed into dressing, in soup, casserole or stew—oysters can be eaten just about any way you can think of. Whole Foods seafood coordinator Jason Hedlund calls them a hyper-local seafood, telling mental_floss, “Oysters reflect the bay they come from, almost like a terroir.” Anyone with the right knife and gloves can shuck their own oysters. Watch this video with George Hastings, a national oyster shucking champion (yes, there is such a thing). 

14. OIL IS LETHAL TO OYSTERS AT ALL STAGES OF LIFE.

Oyster production in the Gulf of Mexico declined each of the four years following the BP oil spill disaster. A report from the National Wildlife Federation, Five Years and Counting, states “…oyster eggs, sperm and larvae were exposed to oil and dispersants during the 2010 oil spill. [Polycyclic aromatic hydrocarbons] can be lethal to oyster gametes, embryos, larvae, juveniles and adults. They can also have sub-lethal effects, such as reduced reproductive success.” Unable to move away from such contamination, sedentary oysters are particularly susceptible.

15. SORRY, YOU'RE GOING TO HAVE TO RELY ON YOUR CHARM.

There is little, if any, truth to the idea that oysters are an aphrodisiac. They contain phosphorus and iodine, which may increase human stamina, and zinc aids in production of testosterone. American and Italian researchers found that a type of mussel related to oysters contains two rare amino acids: D-aspartic acid and N-methyl-D-aspartate, which have been shown to increase sperm motility and stimulate testosterone in mice. But no studies have looked at whether that translates to increased libido. As one of the researchers, George Fisher, professor of chemistry at Barry University, told mental_floss, “To my knowledge, the old-wives tale of eating oysters to improve libido has no sustainable, scientific proof.”