Sydney rock oyster
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| Sydney rock oyster | ||||||||||||||
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 Unconfirmed photo of oysters on a rock at low tide, Wingan Inlet.
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| Saccostrea glomerata (Gould, 1850) |
The Sydney rock oyster, Saccostrea glomerata, formerly known as Saccostrea commercialis, is an oyster species endemic to Australia and New Zealand. In Australia it is found in bays, inlets and sheltered estuaries from Wingan Inlet in eastern Victoria, along the east coast of New South Wales and up to Hervey Bay Queensland., around northern Australia and down the west coast to Shark Bay in Western Australia. There is also a small introduced population on Flinders Island, in Bass Strait, Tasmania and in Albany on the south west coast of Western Australia, where they are farmed. In New Zealand, where the species is not farmed, it is known as the New Zealand rock oyster. The Sydney rock oyster is closely related to Saccostrea cucullata, or hooded oyster, which is common on Indo-Pacific rocky shores.
Sydney rock oysters are capable of tolerating a wide range of salinities (halotolerant). They are usually found in the intertidal zone to 3 metres below the low water mark.
Sydney rock oysters are "broadcast spawners", that is, eggs and sperm are released into open water where fertilisation occurs. Within hours of fertilisation the eggs develop into free swimming planktonic larvae. The larvae swim in estuarine and coastal waters for up to 3 weeks, during which time they develop transparent shells and a retractable foot. The larvae then settle on a clean substrate using the foot to find a suitable site. The foot is resorbed once the larva is attached. The shell darkens and the small animal takes on the appearance of an adult oyster.
Growth rates vary with local conditions, but they generally reach 50 g in 3 years. Sydney rock oysters may change sex during life. Many start out as males and later change to females. About 60% of prime eating oysters are female. Selective breeding has reduced the time to market size from 3 to 2 years. There has also been great success in selection for disease resistance to two protozoan diseases of oysters, namely, QX disease Marteilia sydneyi and winter mortality Bonamia roughleyi.
Oysters are filter feeders, straining planktonic algae from the water. Birds, fish, stingrays, mud crabs and starfish all eat Sydney rock oysters, with the Australian Pied Oystercatcher being particularly fond of them.
There is a thriving commercial oyster farming industry in New South Wales and southern Queensland and a small emerging industry in Albany, Western Australia. The industry produces a gourmet product and provides employment in isolated coastal communities. In Australia, oysters in peak meat condition (i.e. spawning condition) are preferred for the half-shell trade.
