Oysters and Water Pollution

Just one adult oyster can filter and purify 50 gallons of seawater a day. Oysters are particularly effective against nitrogen, which enters oceans through runoff from sewers and agricultural sources. (Nitrogen reduces the oxygen level in the water.) Oysters are happy to “eat” the nitrogen. According to a Woods Hole Oceanographic Institute study, nitrogen ends up in oysters’ shells instead of the water.

Oysters also filter out sediment, which they bundle into small packets and drop onto the ocean floor.

A recent study in Hong Kong, published in the journal Restoration Ecology, found that about 30 square feet of oysters can filter as much water as an Olympic size swimming pool each day.

Oysters and Storm Surges

Natural oyster reefs serve as barriers to protect shorelines from erosion due to storm surges, reducing wave height and strength. (Climate change brings higher tides and stronger storm surges.) A study in Mobile Bay, Alabama, found that oyster reefs reduced shoreline erosion by up to 40 percent. In a study published in Nature Climate Change, oyster reefs scored as the next most effective shoreline protection, second only to coral reefs.

What’s more, a study in Nature Climate Change found that oyster reefs grow faster than sea-level rise, giving them long-term viability.

Oysters and Biodiversity

Those oyster reefs also create homes for a variety of marine life. The Mobile Bay study found significantly more fish around oyster reefs, including sand seatrout, spotted seatrout, red drum, black drum, and significantly more shrimp and blue crabs.

Restoring Oyster Reefs

We have lost about 85% of oyster beds globally since peak harvesting in the 1800s. Groups worldwide are restoring those oyster beds to provide shoreline protection, water pollution reduction, and natural habitats for marine life.

• The Chesapeake Bay Program aims to restore oysters in ten tributaries of the Bay by 2025, as demonstrated in this video.

• In New York City, the Billion Oyster Project is using oyster shells donated by 70 restaurants to rebuild the nearly extinct reefs that once inhabited New York Harbor. Reefs are built by piling oyster shells, usually with something to hold them together, on the seabed, and then “seeding” them with oyster larvae. Just one adult oyster shell can become the home for 20 baby oysters. This CNBC video shows how the project works.

• Even military bases are backing oyster reef restoration, including Naval Weapons Station Earle in New Jersey, Eglin Air Force Base in Florida, and Naval Station Norfolk in Virginia.

• In the U.K., near the Isle of Wight, the Solent Oyster Restoration Project, funded by the Blue Marine Foundation, restores oysters to the Solent Strait, which encompasses several river estuaries and harbors.

• Hong Kong is getting into the act, too, with help from the Nature Conservancy. This video explains how and why.

Not Just Reefs

Although reefs offer the most benefits in terms of shoreline protection, oyster farms that grow oysters vertically – hanging in baskets along a line suspended from the surface—still clean the water.

One successful approach to oyster farming is to grow the oysters along with kelp. Kelp beds protect shorelines by reducing wave energy. Kelp reduces the carbon dioxide in water, reducing acidity and increasing oxygen, all of which help shellfish grow. The healthy microclimate created by kelp beds also attracts fish and other marine life.

The Connecticut-based nonprofit GreenWave has successfully promoted a “regenerative farming” model that combines kelp and shellfish. The number of kelp farms in Long Island Sound more than doubled in the past three years. GreenWave founder Bren Smith explains in his TEDx Talk.

And in the Chesapeake Bay, a new project will allow solar-powered barges to take vertical oyster farming into deeper waters. According to a story this month in the Washington Post, solar energy will drive machinery that rotates oysters to the surface and cleans their cages, reducing labor costs.

Ecosystem Services

When plants and animals change the environment to be better for humans and wildlife, it’s often known as an “ecosystem service.” With projects like oyster reef restoration and regenerative farming, everyone could benefit from oysters’ ecosystem services.