1. The Chesapeake Bay Oyster
Also known as the Eastern Oyster or Crassostrea virginica

2. About Oysters and Oyster Bars
Oysters have 2 shells- are bivalves or pelecypods
Grow about an inch a year
They filter their food which is algae or the microscopic plants in the water (phytoplankton)
An oyster bar is made up of much more than just oysters
oyster with sea squirts attached

3. The Oyster Bar as a Habitat for Other Organisms
1. Oyster spat 2. Skilletfish 3. Hooked mussels
4. Whip mud worms 5. Sea Squirts 6. Sea anemone
7. Barnacles 8. Fan worms 9. Mud crab

4. How Oysters Reproduce
mdsg.umd.edu

5. How we think of the Bay in 1608

6. 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.

7. Oyster Length Changes
Today ” oyster
” oyster

8. The Bay today- Why?

9. 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 among them

10. The Eastern Oyster (Crassostrea virginica)
What is the importance of the oyster?
What has happened to them?
What are we doing about it?

11. 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

12. 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
Overfishing – prior charts
Diseases – both Dermo & MSX are parasitic protozoans
Predators: Crabs, flat worms, toadfish
Pollution
Nutrients: Nitrogen & Phosphates
Can impact preferred plankton food organisms
Algal blooms reduce oxygen at night and through decomposition
Chemicals
Spills may have an immediate effect at the wrong time (specially during larvae set)
Can lock up oxygen
Metals: Trace elements
Affect the young, as in humans
High levels of tin affects settlement of larvae
Sediment: land runoff
settles to bottom covering oyster bar. Oysters adapt by growing long and slender to stay ahead of the silt. Shuckers call them “snappers” due to their thin shells making them difficult to shuck.

13. Changes in the Number of Oysters Harvested from 1840-2000

14. Recent Times- Bushels of Oysters Harvested from 1970-2005

15. 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

16. Dermo disease Perkinsus marinus
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
Dermo – Perkinsus marinus
Parasitic protozoan
First found in VA in 1949; now from Maine to Mexico
Probably introduced by man from another oyster, not natural to the Ches. Bay
Mortalities among oysters highest when water temp is above 25°C and salinity is high, as in years of low rainfall.
Oyster’s natural defenses are overwhelmed at the higher temperatures.
No known effect on humans, even eating raw infected oysters.
Higher mortalities in lower Bay and lower parts of rivers experiencing the higher salinity.
Pollutants seem to have little effect, except as they may reduce the resistance of the oyster.

17. Light infection in the oyster tissue

18. Heavy infection in oyster tissue

19. 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

20. Predators Flat worms Toadfish Crabs (Blue & Mud) Oyster drills Birds
Cow nosed rays
Oystermen
Oyster drills are a bigger problem in the higher salinity water of the lower Bay.

21. 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
Maryland’s sanctuary program places a reef targeted for stocking and monitoring right next to active commercial bars. Sanctuaries are to be closed to commercial harvesting forever. Reserves will be closed initially and opened to harvesting sometime in the future. Approximately 10% of a Reserves’s planted area goes to sancturay status.
The Ches Bay program has a goal of 5,000 acres in the Bay and 1,000 acres in the Potomac of oyster habitat restoration. By 1999, 260 acres of this had been accomplished.
Oysters should be able to grow to larger sizes on these protected bars. Many oysters would grow to about 12 inches in pre-Colonial times. A one-foot oyster produces 1 billion gametes at spawning time, against 10,000 for a 3-inch one.

22. 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!
First line - This is using our native oyster only.

23. Bottom Enhancement
This picture shows 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 over board as the barge is slowly moved across the designated area.This is generally done before the end of June so that the shell is in place prior to the natural spawning that occurs.
Photo courtesy of Chris Judy of the Md DNR.
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.
mdsg.umd.edu

24. Spat on Shell Put into Bay on Oyster Bars
Horn Point Hatchery grows larvae and raises spat
mdsg.umd.edu

25. Larvae are set on shell in containers

26. Spat on shell is put onto oyster bars

27. 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

28. Introduction of Another Species- Example of the Asian Oyster
Crassostrea ariakensis (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
This is only a VA project at this time.

29. 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

30. 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)

31. 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.