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?
Fertilised
egg
Egg
Sperm
Adults
Free swimming
larvae
Spat juveniles
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 2nd and 3rd 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 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. Stomach
2. Heart
3. Mouth-Hinge
4. Adductor Muscle - used to
open and close shell
4
2
1
3
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?
Getting Started
 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
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)
Bed on ice – keep cold!
Eat immediately.
The way of the oyster farmer
Hatchery
Line building
Spat
Maintenance
Grading
Harvest
Sales
Source: Oysters SA http://www.oysterssa.com.au/thesaway2.php?id=82
Growing
Transport
Plankton to plate
the story of edible oysters
What is the
correct
sequence
from plankton
to plate?
1.
2.
3.
4.
5.
8.
11.
6.
9.
12.
10.
13.
7.
Why are oysters important to the
health of an estuary?
Sediment &
other particles
wash from the
land to
waterways
Oysters filter
the
suspended
sediment &
plankton
from the
water
Water quality
is improved
as oysters
remove
material from
water column
Oysters build
healthy
tissue, which
is very
nutritious
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...
 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
GOOD FOR YOU!





low calorie
low fat
low-cholesterol
source of vitamin B12.
complete protein (having all the essential amino acids in the proper
proportions)
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
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