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Sydney Rock Oysters

Sydney Rock Oysters' (Saccostrea glomerata) have a thick shell with a smooth exterier surface which can grow to 8 cm in length. The outside of their shell is smooth and grey coloured. The inside of the shell is smooth and white coloured. There are hinge teeth on the inner margin of their upper shell. The mantle edges and adductor muscle scar are pale coloured.

Sydney Rock Oysters are found on the south-east coast of Australia living near the mouths of rivers. They are capable of tolerating a wide range of salinities. They are usually found in the intertidal zone to 3 metres below the low water mark. Adults live attached to rocks. They eat phytoplankton, zooplankton, bacteria and organic matter by filtering water into their shells and straining the microorganims out.

Their predators are birds, fish (e..g bream), stingrays, octopus, mud crabs, whelks and sea stars.

Sydney Rock Oysters change sex during their lifetime. They start out as males and later change to females. Their first spawning is usually as a male then they spawn as females. During spawning, adult females release up to 20 million eggs and males hundreds of millions of sperms into the water when the tide and current are best for the widest distribution.

The eggs hatch into microscopic, free-swimming and larvae which look for a place to settle in estuarine and coastal waters. By two or three weeks they develop transparent shells and a retractable foot which they use to attach themselves to a suitable hard surface, at this time they are called 'spat'. The foot is reabsorbed once the larva is attached. The shell darkens and the small animal takes on the appearance of an adult oyster. It takes between two and three years for Sydney Rock Oysters to reach maturity with a weight between 40 and 60g.