Sydney rock oyster
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The Sydney rock oyster (Saccostrea glomerata, formerly known as Saccostrea commercialis) is an oyster species endemic to Australia. It is found in bays, inlets and sheltered estuaries from Hervey Bay in Queensland to Wingan Inlet in eastern Victoria. There is also a small population in southwest Western Australia and reportedly another small population on Flinders Island, Tasmania in Bass Strait, Tasmania.
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. Sydney rock oysters generally reach 40–60g in 2–3 years. Sydney rock oysters change sex during life. They start out as males and later change to females. About 75% of prime eating oysters are female. Selective breeding has the potential to reduce growout times by 50%, with inroads being made lately.
They 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.
Whilst there is no commercial harvesting of wild Sydney rock oysters, it is not uncommon to see people with hammer and screwdriver in hand chipping oysters off the rocks for a delicious snack.
All commercial stocks are farmed, with the Sydney rock oyster industry being extremely valuable to regional, coastal New South Wales.
A related species, Saccostrea cucullata, is found throughout the Indo-Pacific region and cultivated for food in Australia and Thailand.
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