1. The Eastern Oyster Crassostrea virginica
Life History, Biology, Ecology, and Culture

2. Oyster Classification
Kingdom – Animalia
Phylum – Mollusca
Class – Bivalvia
Order – Ostreioida
Family – Ostreidae
Genus – Crassostrea
Species - virginica

3. Oyster Life History and Biology
Oysters are selective filter feeders…they trap food particles as water passes by their gills
Primary food – phytoplankton (plant-like plankton)

4. The eastern oyster, Crassostrea virginica, is native to the East coast of Canada and United States, Gulf of Mexico and Caribbean, and as far south as the Northern coast of South America oyster

5. Importance of Oysters
Oysters are known as “keystone” species because they provide habitat for numerous other species
Large numbers of live oysters form a large “reef”
In our area, oyster reefs provide habitat to over 300 other species of aquatic organisms

6. Oyster Life History
Oysters typically spawn in the late spring when the water warms quickly
One adult female oyster produces between 50 and 100 million eggs per spawn
Once a male oyster starts to release sperm, the other oysters start to spawn
Fertilization takes place in the water
Oyster larvae begin to grow a shell within 24 hours of fertilization

7. Oyster Life History cont’d.
The first larval stage of an oyster is called a trochophore larva
The larvae swim around eating phytoplankton and growing over the next 2 weeks (veliger stage)
The larva is ready to settle once it reaches the pediveliger stage
The pediveliger has a “foot” and an eyespot
Once the larva sets on a hard substrate, it attaches and becomes a spat

9. Oyster Restoration
Oysters will settle (set) on any hard substrate but prefer other oyster shells (larvae can taste oyster shell)
For this reason, conservationists and oystermen put old shells back into growing areas (cultch)
Spat – oysters that have set
Numerous spat will set on whole shell and will grow into clumps of oysters
Clumps stand a better chance of survival than single oysters

10. Growing Half-Shell Oysters
Oysters harvested from natural reefs are usually removed from the shells and sold as “meat” by the pint, quart, or gallon
Removing the oyster from the shell (shucking) requires prying the shell open and severing the adductor muscles
Single oysters are preferred for the half-shell market and are shucked just before they are consumed
Single oysters are produced by setting pediveligers on ground up oyster shells (microcultch) as there is only room for one larvae per bit of microcultch

11. Growing Half-Shell Oysters cont’d.
After setting on microcultch, spat are moved to upweller
Upweller – oyster growing system that flows unfiltered bay water through screened silos of spat
Upwellers are either floating models or stationary on shore
Spat grow much faster in upweller due to increased flow of water which means increased food (filter feeders)
After reaching size of thumbnail, seed are transferred to growing baskets in the bay

12. Advantages of Off-Bottom Cages
More sunlight near surface = more photosynthesis = more phytoplankton = more food
More sunlight near surface = more photosynthesis = more oxygen
Near surface = more exposure to air = more oxygen
Near surface = more wave action = more tumbling action
In cages = no predators

13. Growing Gear
Adjustable long-line system (ALLS) – growing cages of oysters are suspended on cable stretched between two pilings
PVC pipes with line clips are set every 10 feet along the run so that the height of the baskets can be adjusted
The space between a set of pipes is called a “bay”
Baskets may be oriented “long-ways” or “cross-ways”
Several different basket designs and manufacturers
Adjustment clips allow for baskets to be raised out of water for air- drying (desiccation)

14. Desiccation Desiccation means to dry something out
If oysters stay in the water all the time, the shell will get covered by fouling organisms
Fouling organisms include algae, barnacles, mussels, mudworms, and other oysters
By air-drying (desiccating) for 24-hours, fouling organisms are killed before they get a chance to grow but oysters are unharmed
Air-dry once a week in warm weather; every 2-3 weeks when cool
Clean shells add value to half-shell oysters

15. Mudworms
The oyster mudworm is a polychaetous annelid named Polydora websteri
The worm secretes an acid that it uses to bore a hole in the shell
The worm leaves a very thin layer between it and the inside of the oyster producing what is known as a mud blister
Sometimes the blister breaks open and you have mud and a live worm in your half-shell oyster – YUK!
Desiccation can be used to control mudworms

16. Growing Gear cont’d.
Oyster-Gro system – uses separate cages that are attached to floating pontoons
Some use 4 bags per cage (mini) while some use 6
Cages are strung together in long lines and attached to screw-type anchors
Pontoons have caps that can be removed to sink units during hurricane
Units are flipped for desiccation

17. Tumbling Oysters
Oysters grow very fast here and the outer edge of the shell is thin
When oysters are shucked, pieces of the thin shell break off and get in meat
Tumbling knocks off thin edge and makes shell thicker
Also encourages a “deeper cup”
Tumbling also grades and washes oysters at the same time
Tumbling should be done 2-4 times during growing cycle

18. Oyster Anatomy and Features
Mantle – the structure that makes the shell
Oysters breathe using both their gills and mantle
They also feed using their gills
An adult oyster can filter 4 liters of water per hour
Protandry – oysters start off their lives as males and turn into females later in life.
If adult oysters are kept cold and wet, they can live for several months out of water

19. Genetic Manipulation of Oysters
Heredity – the traits or characteristics that can be passed from parents to offspring
Gene – segment of a DNA molecule that codes for one trait
Chromosome – a long chain of genes that are braided together to prevent tangling
Diploid – most organisms that reproduce sexually (males and females) have two complete sets (pairs) of chromosomes (one set is inherited from each parent)
Tetraploid – a genetic anomaly in which the organism has four sets of chromosomes instead of two

20. Ploidy of Oysters Oysters are normally diploid just like we are
Populations of tetraploid oysters have been found and studied
It was discovered that if a diploid oyster is cross-bred with a tetraploid oyster, the resulting offspring are triploid (3 sets of chromosomes)
Triploid oysters do not reproduce (spawn) and therefore do not produce eggs or sperm
Oysters are not normally eaten during the warmer months because they are either full of eggs or sperm or they recently spawned and are “empty” (the meat is poor in quality either way)
Triploid oysters are meaty all year as they don’t spawn and grow faster as a result

21. Oyster Predators
Other filter feeders are the main predators on oyster larvae
Predators of adult oysters include stone crabs, blue crabs, black drum, cow nose rays, and oyster drills

22. Oyster Drills Thais haemostoma
Phylum – Mollusca
Class – Gastropoda
Oyster drills get their name from a hard mouthpart called a radula
They use their radula to drill a hole in the oyster’s shell
They secrete enzymes that liquefy the oyster and suck it out through the hole
An adult drill can eat one oyster every three days

23. Oyster Harvesting Regulations
The state health department will often close oyster harvesting following periods of heavy rainfall due to high bacteria/virus counts
In Alabama, oyster farmers are required to obtain the use of private oyster riparian rights
In Alabama, oyster riparian rights extend out to 1800 feet from shore
The ABHS oyster farm site is located at Point aux Pins
The trade name for ABHS half-shell oysters is “Bonus Point” oysters