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The eastern oyster is one of the most iconic species in the Chesapeake Bay. For more than a century, oysters have made up one of the region’s most valuable commercial fisheries, and the filter-feeder continues to clean our waters and offer food and habitat to other animals. But over-harvesting, disease and habitat loss have led to a severe drop in oyster populations. Scientists are working to manage harvests, establish sanctuaries, overcome the effects of disease and restore reefs with hatchery-raised seed in an effort to bring back the bivalve.

Why are oysters important to the Chesapeake Bay?

You don’t have to like eating this peculiar-looking bivalve to appreciate its vital role in the Chesapeake Bay ecosystem and its importance to people in the region.

Oysters filter water 

Oysters are natural filter feeders. This means they feed by pumping water through their gills, trapping particles of food as well as nutrients, suspended sediments and chemical contaminants. In doing so, oysters help keep the water clean and clear for bay grasses and other aquatic life. One oyster can filter more than 50 gallons of water in a single day.

Oysters offer habitat and food

As oysters grow, larvae settle on top of adults, forming layers of oysters that spread upward and outward. With their countless nooks and crannies, these aquatic reefs provide habitat to hundreds of critters, from small fish and invertebrates seeking shelter to larger fish looking for food.

Oysters have a number of natural predators:

  • Anemones, sea nettles and other filter feeders feed on oyster larvae
  • Flatworms and mud crabs feed on new spat
  • Blue crabs and some fish feed on older spat and first-year oysters
  • Shorebirds feed on adult oysters exposed on intertidal flats

Oysters are historically and economically important

Since the late nineteenth century, the oyster industry—including the catch, sale, shucking, packing and shipping of oysters—has contributed millions of dollars to the region’s economy. Oysters have also added to the region’s historical and cultural heritage, inspiring the unique design of the skipjack and fueling countless bull and oyster roasts.

What caused the Chesapeake Bay's oyster population to decline?

The decline of the Chesapeake Bay’s native oyster population can be attributed to several factors, including historic over-harvesting, disease and habitat loss. The severity of this decline is often illustrated in terms of its impact on water quality: in the late nineteenth century, the Bay’s oysters could filter a volume of water equal to that of the entire Bay in three or four days; today’s population takes nearly a year to filter this same amount.

Historic over-harvesting

In the seventeenth century, huge numbers of oysters lived in the Bay. European settlers reported enormous oyster reefs that thrust up from the Bay’s bottom, posing navigational hazards to their ships. Colonists first used hand tongs to harvest oysters, but by the 1800s, dredges were also in use. In the 1850s, more than 1.5 million bushels of oysters were harvested from the Bay each year; three decades later, this number jumped to 20 million. At the turn of the twentieth century, the Bay’s oyster fishery was one of the most important in the United States.

But over-harvesting removed huge volumes of oysters from the Bay and led to the demise of the Bay’s healthy reefs. Because these reefs have been scraped away by dredges, oyster beds are now often limited to flat, thin layers of dead shell and live oysters spread over the Bay’s bottom. These damaged habitats offer less surface area for reef-dwelling critters to inhabit, and can be easily buried by sediment.


In 1949, scientists discovered Dermo in the Bay. MSX was discovered in the region a decade later. Dermo, or Perkinsus marinus, is a parasite that most often infects oysters during their second year of life, causing slowed growth rates and death. MSX, or Haplosporidium nelsoni, also leads to oyster death, but can affect oysters of all ages. Both diseases are contracted between May and October, and their prevalence can be affected by water temperature and salinity.

Overcoming the effects of Dermo and MSX has posed a challenge to oyster restoration. It is estimated that by age three, 80 percent or more of a single oyster year class in a high disease area (like the Virginia portion of the Bay) will die due to disease.

Habitat loss

Over the past century, the watershed has experienced a change in land use, as urban, suburban and agricultural areas have replaced forested lands. This has increased the amount of nutrients and sediment entering our rivers and streams and contributed to the poor water quality that affects aquatic life. Excess nutrients, for instance, fuel the growth of algae blooms that create low-oxygen “dead zones” that hinder the development of oyster larvae; sediment can suffocate oysters and other shellfish. Stress related to poor water quality can make oysters more susceptible to disease.

How are oysters being managed and restored?

In 2005, the Chesapeake Bay Program adopted the 2004 Chesapeake Bay Oyster Management Plan. This plan has four components, including managing oyster harvest, establishing oyster sanctuaries, overcoming the effects of disease and restoring reefs with hatchery-raised seed.

In 2010, Bay Program partners embarked on a tributary-based restoration strategy that will build, seed and monitor reefs in several Maryland and Virginia waterways.

Managing oyster harvest

Managing oyster harvest can ensure the region’s oyster industry remains sustainable. This requires estimating the amount of oysters that can be taken from the Bay without compromising restoration efforts or population size. In Maryland, harvest is managed by the Oyster Advisory Commission; in Virginia, it is managed by the Marine Resources Commission.

Establishing oyster sanctuaries

Oyster sanctuaries are underwater reefs from which shellfish harvesting is prohibited. When a reef is designated a sanctuary, it is often improved by scientists who clean off excess sediment or add shells or other materials for new spat to settle on. Restoring reefs and protecting them from harvest has the potential to increase populations of spawning adult oysters and, in turn, larval production in the Bay.

In the short term, the success of sanctuaries will be limited by disease and poor water quality. But sanctuaries will make important contributions to restoration if disease resistance evolves in wild oysters over time and is supported by management practices.

Overcoming disease

Maryland and Virginia must confront different challenges when it comes to oyster disease. While the prevalence of disease in Maryland waters is dependent on weather conditions, oysters in the warmer, saltier waters of Virginia are faced with constant disease pressure. But research from the Virginia Institute of Marine Science (VIMS) has found that oysters subject to high disease pressure are developing disease resistance, and efforts are underway to breed greater distance resistance in native oyster strains.

Restoring oyster reefs

In 2010, Bay Program partners embarked on a tributary-based restoration strategy that will build, seed and monitor reefs in several Maryland and Virginia waterways. Harris Creek, a Choptank River tributary located on Maryland’s Eastern Shore, was the first site selected for this restoration effort. In September 2015, the Maryland Oyster Restoration Interagency Workgroup reported that reef construction and seeding for Harris Creek’s 350 targeted acres was complete.

Current restoration goals

As part of the 2014 Chesapeake Bay Watershed Agreement, Chespeake Bay Program partners committed to the goal of restoring native oyster habitat and populations in 10 tributaries by 2025.

Take Action

For Chesapeake Bay restoration to be a success, we all must do our part. Our everyday actions can have a big impact on the Bay. By making simple changes in our lives, each one of us can take part in restoring the Bay and its rivers for future generations to enjoy.

To restore oysters in the Bay watershed, consider recycling oyster shell so it can be used to build new reefs. Homeowners with access to a pier or dock can also raise oyster larvae at home, through oyster gardening programs operated by Maryland’s Smart, Green and Growing office or the Chesapeake Bay Foundation. As they grow, these oysters will filter local waters; once they are large enough, they will be used to restock reefs.



Chesapeake Bay News

In The Headlines

Restoring Oyster Reefs

In 2010, Chesapeake Bay Program partners embarked on a tributary-based restoration strategy that focuses on the large-scale restoration of oyster reefs in Maryland and Virginia waterways. The Chesapeake Bay Watershed Agreement oyster outcome aims to restore and protect oyster reefs in 10 tributaries by 2025. Six tributaries have been selected for large-scale oyster restoration, and restoration work has begun in four of these tributaries.

Bay 101: Oysters

February 15, 2012

Oysters are one of the most recognizable species in the Chesapeake Bay, and one of the most important to the health of its ecosystem. Don “Mutt” Meritt from the University of Maryland explains the environmental role that oysters play and describes what scientists are doing to restore the iconic bivalve. Learn more about the Eastern Oyster in the Chesapeake Bay Program’s online Field Guide.

From the Field: Rebuilding oyster reefs in Harris Creek, Md.

March 18, 2013

March 2013: Harris Creek, a tributary of the Choptank River on Maryland’s eastern shore, is the initial site of one of the largest restoration projects ever undertaken in the Chesapeake Bay. Interviews include Mike Naylor (Maryland Department of Natural Resources), Stephanie Reynolds Westby and Jay Lazar (National Oceanic and Atmospheric Administration), Claire O’Neil and Jeff Price (U.S. Army Corps of Engineers), Melissa Grant (University of Maryland Center for Environmental Science, Horn Point Oyster Hatchery) and Doug West (Oyster Recovery Partnership).
Closed Captions: http://www.youtube.com/watch?v=U8TNeusghYs

Chesapeake Stories: A Look Back with Arthur Tuers

November 13, 2009

At 79 years old, Arthur Tuers has been fishing, crabbing, and boating the Chesapeake Bay for most of his life.  He began working at McNasby’s Oyster Company at age 10, and he has seen the oyster harvests plummet over the decades.  Art has also noticed dramatic changes in the clarity of water, the difficulty of crabbing, and amount of overall pollution in the Bay.


Ecosystem Effects of Oyster Restoration in Virginia Habitat and Lease Areas

Publication date: June 01, 2006 | Type of document: Report | Download: Electronic Version

This report is the third in a series in which the Chesapeake Bay Environment Model Package was used to assess the environmental benefits of oyster restoration in the Chesapeake Bay. Here, the effects of oyster restoration to all potential…

2004 Chesapeake Bay Oyster Management Plan

Publication date: December 05, 2005 | Type of document: Report | Download: Electronic Version

The Oyster Management Plan includes both a general framework and specific guidance for managing and rebuilding the native oyster stock in Chesapeake Bay. The development of the plan was a multi-partner endeavor by representatives from state…

Evaluating Ecosystem Effects of Oyster Restoration in Chesapeake Bay-A report to the MD DNR

Publication date: September 01, 2005 | Type of document: Report | Download: Electronic Version

The Chesapeake Bay Environmental Model Package (CBEMP) was used to assess the environmental benefits of oyster restoration in Chesapeake Bay. The CBEMP consists of a coupled system of models including a three-dimensional hydrodynamic model,…

Assessing a Ten-Fold Increase in the Chesapeake Bay Native Oyster Population

Publication date: April 01, 2005 | Type of document: Report | Download: Electronic Version

The Chesapeake Bay Environmental Model Package (CBEMP) was used to assess the environmental benefits of a ten-fold increase in native oysters in Chesapeake Bay. The CBEMP consists of a coupled system of models including a three-dimensional…

Apoption Statement - 2004 Oyster Management Plan

Publication date: January 10, 2005 | Type of document: Adoption Statement | Download: Electronic Version

An adoption statement signed by the Executive Council to continue the 2004 Oyster Management Plan.  The 2004 Oyster Management Plan provides both a general framework and specific guidance for rebuilding and managing the native oyster,…

Non-native Oysters and the Chesapeake Bay

Publication date: August 14, 2003 | Type of document: Fact Sheet | Download: Electronic Version

While Chesapeake Bay Program partners continue their work to restore native oysters, efforts are also underway to better understand the risks and benefits surrounding the possible introduction of non-native oysters into the Bay. This…

Recommendations on Suminoe Oyster (Crassostrea Ariakensis) Aquaculture in Chesapeake Bay

Publication date: April 23, 2002 | Type of document: Fact Sheet | Download: Electronic Version

The purpose of this document is to communicate the findings and recommendations of the Federal Agencies Committee of the Chesapeake Bay Program with respect to an anticipated proposal to introduce the Suminoe oyster into the waters of the…

Chesapeake Bay Program Oyster Restoration: Workshop Proceedings and Agreement Statements

Publication date: March 01, 2000 | Type of document: Report | Download: Electronic Version

Report curtailing proceedings and agreement statements on oyster restoration derived from 2 day workshop held in Waldorf, MD on January 13 & 14, 2000. Contains important consensus statements derived from meeting, on oyster sanctuaries and…

Annual Progress Report: Fishery Management Plans 1994

Publication date: October 01, 1995 | Type of document: Management Plan | Download: Electronic Version

As part of the process of establishing accountability and tracking the implementation of management actions, each fishery management plan (FMP) is annually reviewed and updated. This report reviews the progress of management plans during…

Oyster Fishery Management Plan (1994)

Publication date: January 01, 1994 | Type of document: Management Plan

The goal of the 1994 Oyster Fishery Management Plan is to enhance the production of oysters in the Chesapeake Bay ecosystem by restoring habitat, controlling fishing mortality, promoting aquaculture and continuing the repletion programs.

Oyster Fishery Management Plan (1989)

Publication date: July 01, 1989 | Type of document: Management Plan

The purpose of the Plan is to manage the oyster resource by restoring oyster habitat, controlling fishing mortality, promoting aquaculture and continuing the repletion programs.

From Around the Web

Bay FAQs

  • What is ocean acidification?
  • Why has the Chesapeake Bay’s oyster population declined over time?
  • What is the ideal salinity for eastern oysters?
  • What is an example of a benthic community?


Bay Terms

  • Aquatic reef
  • Bivalve
  • Chemical contaminants
  • Dermo
  • Ecosystem
  • Filter feeder
  • MSX
  • Sediment
  • Sedimentation
  • Spat


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