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

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

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)

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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