Oysters reefs

If someone says reef, most people will immediately think of coral reefs, but there are reefs based on oysters too.

Page Contents

1 Background
2 Services
- 2.1 Summary of services provided for us:
3 Threats to the services?
4 What can we do to retain these services?
5 Dig deeper

Background

What are oysters?

Oysters are a type of mollusc. What most people think of, when they visualise an oyster, is a marine mollusc/shellfish with two shell halves (valves) hinged together with a soft body enclosed between them. The shells are rough and thick. There are, in fact, about 200 species of shellfish that are classified as oysters, but almost all research has been carried out on edible species and pearl producing oysters and a few others that have commercial value.

Oyster anatomy, Feeding and Reproduction

The image "The anatomy of the oyster" shows the mantle, gills, heart and adductor muscles as the most prominent features. The adductor muscle holds the two valves of the shell shut. The mantle is multifunctional- gamete formation occurs here, energy reserves are stored here, and the shell is secreted from this tissue. The gills are used for filtering food particles from incoming water and also function as a gas exchange surface. The heart pumps the colourless "blood" to the rest of the tissues. Kidneys, nervous system and rectum not shown.

Through filter feeding, oysters mostly eat phytoplankton. As oysters filter feed, they also pick up nutrients within the water. They easily absorb key vitamins and minerals from their environment including iron, zinc, vitamin B12, calcium and selenium.

Oysters reproduce by sexual reproduction with eggs and sperm released into the water to fertilise. After several weeks of growing as free swimming larvae, oyster juveniles aggregate together by fastening themselves to rocks and to each other. Other species such as sea anemones, mussels, and barnacles then settle on them and attach themselves to any available surface. This makes oysters keystone species in the community as they are the foundation of the entire assemblage.

oyster life cycle illustration — oyster life cycle

Oyster distribution

Oyster reefs are found in coastal (always covered by water) and estuarine (exposed during low tide) waters all over the globe.

Services

Forming an oyster reef creates an abundant food source and shelter for other creatures including many commercially valuable food species. This protection is especially valuable when the fish, crabs and other inhabitants are at the nursery stage and very vulnerable to predation.

Oysters are filter feeders and a single oyster can filter around 5 litres of water per hour/180 litres of sea water per day to gather food. Great banks of oysters can make the surrounding water clearer, making it easier for sea grasses and other plants that need light to survive underwater. Oysters also bioaccumulate toxins and pollutants through their filtration.

Densely packed beds and reefs of oysters are natural breakwaters, absorbing wave energy and boat wakes thus dramatically cutting the heights of waves arriving at beaches. In intertidal areas, they can lessen damage to sandy shoreline , preventing erosion and protecting marshes.

Because they are pivotal in providing these services, oysters are regarded as a keystone species.

Oysters also produce raw material - pearls and mother of pearl, for adornment items. Recently, in Western Australian, where there is an established pearling industry, mother-of-pearl is being investigated as a new form of synthetic bone for people who need bone grafts/reconstructive surgery.

Summary of services provided for us:

Food - Both the oysters themselves and other edible species sheltered in the reefs
Erosion Control - Acting as breakwaters, lessening beach erosion and marshland disruption
Water quality - Filtering water and improving water quality for other species
Aesthetic services - Production of pearls and mother-of-pearl
Biomedical material - Use of mother-of-pearl as a bone substitute.

Threats to the services?

On a global scale, 85 - 90% of oyster reefs have been damaged

by humans intensively harvesting oysters for food
through habitat disturbance such as channel dredging and oil spills
by knock on effects from climate change

What can we do to retain these services?

Regulating wild oyster harvesting
Consideration of oyster beds when planning facilities such as marinas
Ensuring all oyster farms are sustainably managed
Protection of surviving reefs
Restoration projects

Dig deeper

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