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The Chesapeake Bay Oyster

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The Chesapeake Bay Oyster. Also known as the Eastern Oyster or Crassostrea virginica. About Oysters and Oyster Bars. Oysters have 2 shells- are bivalves or pelecypods Grow about an inch a year

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The Chesapeake Bay Oyster

Also known as the Eastern Oyster or Crassostrea virginica

About Oysters and Oyster Bars
  • Oysters have 2 shells- are bivalves or pelecypods
  • Grow about an inch a year
  • They feed by filtering microscopic plants out of the water (phytoplankton)
  • An oyster bar is made up of much more than just oysters

oyster with sea squirts attached

the oyster bar as a habitat for other organisms
The Oyster Bar as a Habitat for Other Organisms

1. Oyster spat2. Skilletfish3. Hooked mussels

4. Whip mud worms5. Sea Squirts6. Sea anemone

7. Barnacles8. Fan worms9. Mud crab

Our Oyster 400 Years Ago
  • Extensive oyster beds covered the higher salinity parts of the Bay.
  • In the Chesapeake, oysters were so numerous that they are thought to have been able to filter the water in the entire Bay in a few days.
  • It is also said that the reefs they formed were so large, they were a hazard to navigation in some areas.
  • The bars provided an extensive habitat for a variety of animals including barnacles, anemones, mud crabs, gobies and blennies.
  • It was not uncommon for oysters to be 8-10 inches in length.
Oyster Length Changes

Today 3.75” oyster

1608 8-10” oyster

Changes in the Chesapeake Bay with the Decline of the Oyster
  • Less filtering so more algae in the water
  • More algae means cloudier water
  • When the algae dies, it sinks to the bottom where it is decomposed by bacteria
  • Bacteria use up oxygen and cause hypoxia (low dissolved oxygen) or anoxia (no dissolved oxygen) in the water
  • Low DO (dissolved oxygen) is bad for organisms that live there
  • Less oysters means loss of habitat for those organisms that live on and amongthem
the eastern oyster crassostrea virginica
The Eastern Oyster(Crassostrea virginica)
  • What is the importance of the oyster?
  • What has happened to them?
  • What are we doing about it?
oyster s contribution to the ecosystem
Oyster’s Contribution to the Ecosystem
  • Fishery – an obvious and valuable natural resource
  • Filtering
    • - Nutrient reduction
    • - Improved water clarity
    • - 17th Century: Bay filtered ~ every few days
    • - 21st Century: ~ a year or more
  • Habitat

- Wide range of species

- Contributes to health of the food chain

why is the oyster population declining
Why is the Oyster Population Declining?
  • Overfishing
  • Diseases
    • Dermo
    • MSX
  • Predators
  • Pollution-nutrients, chemicals, metals, sediment
  • Habitat degradation and loss
  • Failure of natural spat sets- larvae that settle don’t survive
  • The quality of the water has affected the Bay and the oysters
diseases attributed to the oyster decline
Diseases Attributed to the Oyster Decline
  • MSX and Dermo-
  • Both are warm water diseases
  • They thrive for about 5 months out of the year in the
  • Chesapeake Bay
  • MSX prefers higher salinity (>15 ppt)
  • MSX is an occasional problem
  • Dermo prefers higher salinity (>12 ppt)
  • Dermo generally does not kill young oysters
  • Dermo is a chronic disease
dermo disease
Dermo disease


  • Parasitic protozoan (single cell)
  • Prefers high salinity & temperature
  • Reaches its peak in late summer
  • Not lethal to oysters at low to moderate levels
  • Not harmful to humans
  • Has been around since the 1940’s
Working around Disease
  • Plant oysters in lower-salinity areas
  • Use fast-growing oysters that can outgrow Dermo disease
  • Develop and use oysters that are more tolerant of disease or are resistant
  • Flat worms
  • Toadfish
  • Crabs (Blue & Mud)
  • Oyster drills
  • Birds
  • Cow nosed rays
  • Oystermen
types of bars sanctuaries reserves commercial
Types of Bars-Sanctuaries, Reserves, Commercial
  • Sanctuaries are fully protected
  • Managed reserves may be harvested
    • Generally near commercial bars
    • Stocked & monitored
    • Provide increased brood stock (oysters that will reproduce)
  • Commercial bars are open to licensed watermen using legal harvesting techniques
actions to help the oyster
Actions to Help the Oyster
  • Breed for better disease tolerance
  • Build more sanctuaries and reserves
  • Enhance bottom- more hard surface
  • Mass setting & planting
  • Possible moratorium on all commercial harvest
  • Expand oyster gardening- growing oysters at docks in cages
  • Oyster aquaculture as a business
  • Investigate alternative species – Asian oyster and the answer is no!
Bottom Enhancement

Chris Judy of the Md DNR

  • Oyster shells that were dredged up from deep water deposits in the Bay and transported by barge to an area of known good spat setting.
  • Water cannons blow the shell overboard as the barge is slowly moved across the designated area.

Spat on Shell Put into Bay on Oyster Bars

Horn Point Hatchery grows larvae and raises spat

Larvae are set on shell in containers

Spat on shell is put onto oyster bars

restoration by watermen
Restoration by Watermen
  • Production of small amounts of spat on shell for planting
  • In 2009, the pilot program at Morgan State produced 3 million spat for planting by the Calvert County watermen
introduction of another species example of the asian oyster
Introduction of Another Species- Example of the Asian Oyster

Crassostreaariakensis(Suminoe oyster)

  • VIMS project
  • Proven disease resistance in Asia and Virginia
  • Using sterile triploid oysters
  • Problem: Introduction of a non-native species
  • Expanded trials in 2003 used 1 million oysters
  • In 2009, it was decided that this project would stop and the oysters WOULD NOT be introduced
aquaculture as an alternative
Aquaculture as an Alternative
  • The Maryland Oyster Advisory Commission’s 2008 report recommends “Developing a transparent and balanced transition strategy for growing Maryland’s oyster industry based primarily on aquaculture.”
  • Requires less regulations on equipment, harvest season, maximum catch, minimum length
  • Oysters achieve market size much faster which helps prevent mortality by the parasites (MSX and Dermo)
  • Aquaculture has met with some success in Virginia
methods of aquaculture
Methods of Aquaculture
  • Spat on Shell (lease oyster reefs, watermen plant and harvest oysters)
  • Bottom Cage Culture (oysters grown in cages on leased bottom)
  • Floating Cage Culture (oysters grown in floating cages, or suspended in the water column)
Hopefully, the efforts of resource managers, local and regional organizations, scientists and community members will be successful in restoring our native oyster to a reasonable fraction of it’s former abundance and vitality.

However, it has been a difficult struggle up to this point – we still have a long way to go and much to learn.