The story of edible oysters

What are oysters? Marine / estuarine animal Shell (mollusc) Bivalves (2 shells) Omnivore (eats both phytoplankton and zooplankton) Size: 8cm-36 cm (depending on the species) Immobile after the oyster larvae has settled

What is the purpose of the shell ? The shell is the only protection for the oyster from predators Helps the oyster retain moisture when the tide drops. A mini-habitat for other living things to grow.

Where do they come from? Adults Spat - juveniles Sperm Egg Fertilised egg Free swimming larvae

Oysters swopping sexes All oysters start off life as males Oysters become adults when they are 1 year old, and produce sperm in their first year of spawning As oysters grow older, they switch from being males, and become females In their 2 nd and 3 rd years of life, these female oysters produce eggs Over 75% of prime eating oysters are females

How do oysters feed? Oysters are filter feeders They filter s uspended sediment and plankton Oysters trap suspended sediment & plankton on mucus on their gills This material is transported to the mouth and then enters the stomach Waste is excreted through the anus

Identifying the parts of an oyster All species of oysters share the same common anatomical parts. Protecting the animal there is a right shell and a left shell. The right shell is the top shell. The left shell is the one attached to the substrate and is called the bottom shell or cup.

Can you identify the internal parts? Stomach 2. Heart 3. Mouth-Hinge4. Adductor Muscle - used to open and close shell

Oyster Predators  Oysters have several predators, including: Carnivorous sea snails (e.g. Mulberry whelk, Oyster drill) Sea stars that open oyster shells by exerting continued pressure on the shells Mud crabs that open oyster shells using their strong pincers. Australian Pied Oystercatcher, a marine bird that has a beak adapted for prising open oyster shells Fish including stingrays

What do we know so far? Anatomy of the oyster Filter the estuary water Provide habitats for other organisms Important in the estuary food chain.

Growing oysters Water quality is very important to growing oysters. What washes off the land influences the water. Therefore, what happens within a catchment can impact on the quality and health of local oysters. Oysters are not fed or treated with any chemicals throughout their lifetime.

Farming Oysters What does an oyster farm look like?

The Sydney rock oyster ( Saccostrea glomerata ) is considered a gourmet's delight and is the main focus of oyster production in NSW Four different cultivation methods exist: 1) Stick culture where larvae settle on sticks 2) Tray culture where oysters are grown in trays that are laid on racks 3) Basket culture where oysters are grown in containers that are attached to long-lines made of rope 4) Raft culture which allows stacked trays of oysters to hang from a floating structure Getting Started Oyster farming is the most valuable aquaculture industry in New South Wales NSW production valued at $42.3m

Food safety Healthy oysters are sold by farmers when water quality tests indicate that water quality is good. Eating oysters from rocks is not safe as you don’t know how clean the water is. Eating a contaminated oyster can make you sick. Fresh oyster: Proper storage- cold dry environment – refrigerate Closed shell Scrub and rinse shell Shuck (open the shell) Shuck Bed on ice – keep cold! Eat immediately.

The way of the oyster farmer HatcherySpatGradingGrowing Line building MaintenanceHarvest Sales Transport Source: Oysters SA

Plankton to plate the story of edible oysters What is the correct sequence from plankton to plate?

Why are oysters important to the health of an estuary? Water quality is improved as oysters remove material from water column Oysters filter the suspended sediment & plankton from the water Oysters build healthy tissue, which is very nutritious Sediment & other particles wash from the land to waterways Food for thought! The oyster has been referred to as the canary of the waterways because its health is determined by the health of the water in which it grows.

What affects healthy oysters? Water too warm. Water too fresh Water polluted

Water too warm? Warming sea temperatures Climate change leads to shift of species Could lead to the introduction of marine pests and other animals that compete for food and space ‘Ocean acidification’ – oyster shells (made from calcium carbonate) could dissolve as oceans become more acidic

Impacts on oysters and the oyster industry from Climate Change Strengthening of the East Australian Current Rainfall changes Increasing frequency of heat waves Sea level rise Acidification of sea water

Water too fresh? Urban development has increased the amount of freshwater that runs-off the land into the waterways This freshwater run-off contains pollutants that are washed off the land Freshwater bloats oysters, reducing the quality of this seafood

Water too dirty Sediment washed off the land can smoother oysters and other marine animals and plans such as seagrass Pollution comes in many forms. Most notably for oysters is effluent from sewage overflows, cattle accessing creeks, birds and dog-poo Increased nutrients from fertilisers washing off farms and gardens may cause high algal growth and can result in very low oxygen levels in the water when the algae decompose Chemical contamination from industrial leaks or chemical dumping

Contaminants that enters an estuary will affect an oysters health Water-based pollution -Oil and fuel spills from boats Land-based pollution -Stormwater run-off -Sewage overflows -Cattle effluent in creeks -Fertilisers -Pesticides -Dog poo -Sediments displaced due to erosion ‘Oyster health declines’ Click here to investigate the issues facing our estuaries further

One Oyster calories. Carbohydrate grams fat calories grams protein calories grams vitamin B12 (120 percent of your daily recommended value) rich in three minerals: zinc, copper and selenium (33-55% of daily requirement)

The Oyster Plate low calorie low fat low-cholesterol source of vitamin B12. complete protein (having all the essential amino acids in the proper proportions) GOOD FOR YOU!

Recap and Review The anatomy of an oyster The oyster environment Role of the oyster – its place in the estuary food web Oyster farming Nutritional value Eating oysters END of PRESENTATION - Photos used have been supplied from copyright free sources however the producer of this power point claims no ownership of this property. - It is a free resource.