Eastern Oysters

Learn why oysters are important to the Chesapeake Bay, the history and current state of oyster populations, and why it’s important to restore oyster reefs.

Why are oysters important for the Chesapeake Bay?

Eastern oysters, Crassostrea virginica, are a critical component of the Chesapeake Bay ecosystem, known as a keystone species. The reefs that oysters form provide important habitat for the Bay’s fish, crabs, worms, and other animals. Oysters are also prolific filter feeders that remove light-blocking algae from Bay waters and help remove excess nutrients like nitrogen and phosphorus.

In other words, more oysters equal better water quality. Without oysters, the quality of the Bay ecosystem suffers. Without oyster filtration clearing the water for light to penetrate, bay grasses can struggle to grow. Without oyster reef habitat that provides refuge from predators and ample prey to feed on, juvenile fish and crabs may not survive to adulthood.

Humans are affected, too. Without a thriving oyster population, the seafood industry that has relied upon Chesapeake Bay oysters for hundreds of years will continue to struggle.

What happened to oysters in the Chesapeake Bay?

Currently, oyster populations in the Bay are at a small fraction of their historical population size. The storied shellfish and their vertical reefs once posed navigational hazards to early Europeans sailing in the Bay. Their abundance created a Chesapeake oyster-harvesting industry that became the largest in the world by the late 19th century.

But decades of overharvesting, pollution, and disease have contributed to the decline of oyster populations in the Bay. Destructive harvesting techniques led to the loss of roughly three-quarters of the Bay’s oyster reefs between 1860 and 1920. Then, beginning in the 1950s, the Bay was hit with two diseases—MSX and Dermo—that are caused by parasites that attack and frequently kill oysters, though they are harmless to people. Together with continued overharvesting and pollution, the diseases devastated the Bay’s oyster populations.

What is the current state of oyster populations in the Chesapeake Bay?

In Maryland, the overall oyster population is down from 600 million market-size oysters in 1999 to about 400 million in 2020, according to a June 2020 update to Maryland's Oyster Stock Assessment by the Maryland Department of Natural Resources. But the estimated number of oysters less than one year old is the sixth lowest recorded since 1999—about 275 million oysters—which could spell trouble for future harvests.

Virginia's total wild oyster harvests have remained stable at around 600,000 bushels for the past several years, partly due to a rotational harvest system. This system reduces pressure on certain harvest bars by only opening them to harvest once every three years. In addition, a state supported replenishment program helps to plant shell on harvest areas, increasing habitat for baby oysters (spat) to attach and grow. Why is it important to restore oysters and oyster reefs?

Unfortunately, oyster populations have remained at low levels for many years. In some areas, populations continue to decline. But the good news is that when we bring back oysters, all of their benefits come back with them.

Why is it important to restore oysters and oyster reefs?

Unfortunately, oyster populations have remained at low levels for many years. In some areas, populations continue to decline. But the good news is that when we bring back oysters, all of their benefits come back with them.

An 80 percent increase in seafood harvest is estimated in Harris Creek compared to pre-oyster-restoration levels.  Graphic credit: copyright Chesapeake Bay Foundation

In 2014, Maryland and Virginia each committed to restoring oyster populations and reef habitat in five rivers in each state by 2025. Areas in which this large-scale oyster restoration has been carried out to bring back oyster reefs and restore their function in the ecosystem are starting to see the benefit of increasing oyster populations and stable or growing reef habitat. In Maryland, restoration efforts are now complete in two out of five rivers and Virginia has completed restoration in one river.

Nitrogen equal to 20,000 bags of fertilizer is removed annually in Harris Creek. That's 12 stacks of bags as tall as the Washington Monument. Graphic credit: copyright Chesapeake Bay Foundation

Restored oyster reefs in Harris Creek, on Maryland’s Eastern Shore, can now filter the entire volume of the creek in less than 10 days during the summer. Each year, the reefs are estimated to remove an amount of nitrogen equivalent to 20,000 bags of fertilizer—a service valued at more than $1.7 million.

Pollution, habitat loss, overharvesting, and disease are the main factors limiting oyster recovery in the Chesapeake Bay. Full implementation of the Chesapeake Bay Clean Water Blueprint, the science-based plan to restore the Bay to health, is the primary means by which we can achieve improved water quality and reduce the threats to oyster survival.

Until oyster populations improve enough to replenish oyster reefs on their own, we will need to continue restoration efforts by placing shell and juvenile oysters on the bottom to kickstart the process. 

How can I help oysters recover in the Chesapeake Bay? 

There are many ways you can help us restore oyster populations and improve water quality in the Bay:

  • SPREAD the word to your neighbors and friends about how important oysters are to the health of the waters and wildlife of the Bay. 
  • RECYCLE your oyster shells through CBF’s shell recycling program and support restaurants that participate in shell recycling programs—shell is one of the biggest limiting factors in oyster restoration.
  • SUPPORT local oyster farmers by buying directly from local farms, at farmers’ markets or through the Chesapeake Oyster Alliance’s oyster pop-up shops
  • SHARE your support for oyster recovery—and especially the unique value of vertical oyster reefs—by writing a letter in your local paper or to state officials responsible for oyster restoration.
  • VOLUNTEER with CBF's active oyster restoration program by building reef balls, cleaning shells, or becoming an oyster gardener. Visit cbf.org/oysters for more info.
  • MAKE A DONATION to support our oyster restoration program by giving the gift of oysters from our online Giving Catalog at cbf.org/catalog.

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What Should be the Role of Oysters in the Bay Cleanup?

The mighty oyster's capacity for removing excess nutrients from our Bay's waters is well known. But is it enough to consider oysters a player in achieving the pollution reductions of the Chesapeake Bay Clean Water Blueprint? A number of factors need to be understood to engage in such a discussion. CBF's position on using oysters to comply with the Bay Total Maximum Daily Load addresses these factors.

The Bay Needs You

The 2018 State of the Bay Report makes it clear that the Bay needs our support now more than ever. Your donation helps the Chesapeake Bay Foundation maintain our momentum toward a restored Bay, rivers, and streams for today and generations to come.

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Do you enjoy working with others to help clean the Chesapeake Bay? Do you have a few hours to spare? Whether growing oysters, planting trees, or helping in our offices, there are plenty of ways you can contribute.

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