10 Reasons oysters are the most underrated marine creatures

1. Oysters are keystone species aggregating to form complex reef structures

Oysters are keystone species providing habitat, refuge and a foraging ground for invertebrates and fish. As their tiny free swimming larvae begin to settle their shell accumulates over time, forming complex three dimensional reef habitat. 

Remnant flat oyster reef in Port Phillip Bay (photo courtesy Paul Hamer).

2. Oysters have mighty filtration powers

Oysters improve water quality by filtering algae, nutrients and suspended matter in the water column through their gills.  One single oyster filters up to 150 litres of water a day. Now, can you imagine the water filtration capacity of an entire reef! Nature really does do it best. 

3. Oyster larvae "hear" through vibrations

Oyster larvae float around in the water column waiting for the perfect opportunity to settle and grow into an adult. Although oysters don't have ears, they have clever abilities which enable them to sense or "hear" their environmental surroundings. Oysters perceive the vibrations created by sound waves using the statocyst: the organ that registers movement and vibration. 

4. Oysters have three chambered hearts and colourless blood

Oysters breathe much like fish, using both gills and mantle. The mantle is lined with many small, thin-walled blood vessels which extract oxygen from the surrounding water. A small, three-chambered heart pumps colorless blood, with its supply of oxygen, to all parts of the body. At the same time a pair of kidneys located on the underside of the muscle purify the blood of any waste products it has collected.

5. Oyster reefs stabilise shorelines

By forming reef habitat on top of the sediment surface oysters help to stabilise sediment and dampen wave energy, thereby protecting shorelines. Oyster reefs are now being promoted as a nature based solution providing coastal protection and mitigating, and adapting to the effects of climate change.

Ecosystem Services delivered by oyster reefs in Ysebaert 
et al. 2018, Habitat Modification and Coastal Protection by Ecosystem-Engineering Reef-Building Bivalves.

6. Oyster reefs provide homes for hundreds of other marine species

When oysters cement together, their aggregations form complex habitat creating homes for a great diversity of invertebrates, boosting the density and diversity of the little animals that feed the broader coastal food web. They also act as a nursey grounds supporting the growth of commercially important fish species.

7. Aboriginal Australians consumed oysters for thousands of years

Aboriginal oyster farming is likely the oldest form of aquaculture practiced in Australia. Shell middens are commonplace around Australia's coastlines and provide valuable information about Aboriginal use of the coast and can show changes in diet, behaviour, activities and settlement over the last 12,000 years. One of the most important features of midden places is that the shell can easily be dated using the radiocarbon method of dating. The oldest known Aboriginal shell midden place on the Victorian coast is nearly 12,000 years old.

8. Native Ostrea angasi oyster reefs are functionally extinct in Australia

Prior to European settlement much of Australia's coastline was fringed with oyster reefs (also known as shellfish reefs). These reefs were dominated by the native Ostrea angasi flat oyster and were common in South Australia’s gulfs and bays spreading across 1500km of coastline.  Dr Heidi Alleway and Professor Sean Connell from the University of Adelaide dug through historical records to uncover South Australia's rich, but dark, oyster history. As Europeans flocked to Australia's coastlines they brought destructive fishing practices utilising metal dredges as an effective method of scouring the seafloor for oyster shell. Nothing was exempt; the beautifully complex and biodiverse seafloor was annihilated leaving little behind. These native oyster reefs are now considered functionally extinct with one healthy reef remaining in Tasmania.

9. South Australia is home to the largest oyster restoration project in the Southern Hemisphere

South Australia is home to one very large (20 ha to be exact) oyster restoration project: Windara reef, located in the coastal waters of Gulf St Vincent near Ardrossan. It is the largest of its kind in the Southern Hemisphere, made up of 18,000 tonnes of locally sourced limestone providing the initial foundations for reef regeneration. By replacing the hard substrate that once existed in the Gulf, oyster populations can begin to reestablish and thrive. 

10. Oyster reefs are being restored across Australia

Reef Builder, an exciting partnership between the Australian Government and The Nature Conservancy aims to bring shellfish reefs back from the brink of extinction. The $20 million investment will rebuild shellfish reefs around the Australian coastline, three of which are located in South Australia. One of these has been constructed at Glenelg, with two more planned for Kangaroo Island and Onkaparinga. 

Glenelg oyster reef construction (photo courtesy of Maritime Constructions)

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