The Eastern Oyster Crassostrea - PowerPoint Presentation

Slide1

The Eastern OysterCrassostrea virginica

Life History, Biology, Ecology, and CultureSlide2

Oyster ClassificationKingdom – AnimaliaPhylum – Mollusca

Class –

Bivalvia

Order –

Ostreioida

Family –

Ostreidae

Genus –

Crassostrea

Species -

virginicaSlide3

Oyster Life History and BiologyOysters are selective filter feeders…they trap food particles as water passes by their gillsPrimary food – phytoplankton (plant-like plankton)Slide4

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 oysterSlide5

Importance of OystersOysters 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 organismsSlide6

Oyster Life HistoryOysters typically spawn in the late spring when the water warms quicklyOne 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 fertilizationSlide7

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 spatSlide8
Slide9

Oyster RestorationOysters 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 oystersSlide10

Growing Half-Shell OystersOysters 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

microcultchSlide11

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 baySlide12

Advantages of Off-Bottom CagesMore sunlight near surface = more photosynthesis = more phytoplankton = more foodMore 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 predatorsSlide13

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)Slide14

DesiccationDesiccation means to dry something outIf 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 oystersSlide15

MudwormsThe 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

mudwormsSlide16

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 desiccationSlide17

Tumbling OystersOysters grow very fast here and the outer edge of the shell is thinWhen 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 cycleSlide18

Oyster Anatomy and FeaturesMantle – the structure that makes the shellOysters 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 waterSlide19

Genetic Manipulation of OystersHeredity – 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 twoSlide20

Ploidy of OystersOysters are normally diploid just like we arePopulations 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 resultSlide21

Oyster PredatorsOther filter feeders are the main predators on oyster larvaePredators of adult oysters include stone crabs, blue crabs, black drum, cow nose rays, and oyster drillsSlide22

Oyster DrillsThais 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 daysSlide23

Oyster Harvesting RegulationsThe 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