“PLANKTON TO PLATE”

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

SpermEgg

Fertilised egg

Free swimming larvae

Oysters swopping sexesAll oysters start off life as malesOysters become adults when they are 1 year old, and produce sperm

in their first year of spawningAs oysters grow older, they switch from being males, and become

femalesIn their 2nd and 3rd years of life, these female oysters produce eggsOver 75% of prime eating oysters are females

How do oysters feed?Oysters are filter feeders They filter suspended

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?

1

2

3

4

1. Stomach 2. Heart 3. Mouth-Hinge 4. 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

shellsMud 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 oysterFilter the estuary waterProvide habitats for other organismsImportant in the estuary food chain.

Growing oystersWater 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 OystersWhat 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 sticks2) 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 StartedOyster 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)• Bed on ice – keep cold!• Eat immediately.

The way of the oyster farmer

Hatchery Spat Grading Growing

Line building Maintenance Harvest Sales Transport

Source: Oysters SA http://www.oysterssa.com.au/thesaway2.php?id=82

Plankton to platethe story of edible oysters

What is the correct

sequence from plankton

to plate?

2.

1.

3.

4.

5.

6.

7.

8.

9.

10.

13.

12.

11.

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 pollute

d

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 ChangeStrengthening of the East Australian CurrentRainfall changesIncreasing frequency of heat wavesSea level riseAcidification 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...40.8 calories.

Carbohydrate -10.2 grams fat calories -10.4 grams protein calories -20.2 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 calorielow fat low-cholesterolsource of vitamin B12. complete protein (having all the essential amino acids in the proper

proportions)

GOOD FOR YOU!

Recap and ReviewThe anatomy of an oysterThe oyster environmentRole of the oyster – its place in the estuary food webOyster farmingNutritional valueEating 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.