< Previous species

OSTREIDAE

Next species >

Saccostrea glomerata (A. Gould, 1850)      Sydney Rock Oyster

Description: Shell solid, heavy. Shape variable from roughly circular to elongate, Lower (left) valve cup shaped, adherent to substrate and conforming to the surface, upper (right) valve nearly flat. Hinge line short, straight. Interior white, single adductor muscle scar well defined, valves with chomata inside margin (Fig. 2c). Exterior with irregular, coarse radial ribs, surface crumpled. Shell colour dark purple to black.

Size: Up to about 100 mm in height.

Distribution: Southeastern Australia and North Island of New Zealand. In Australia, specimens of confirmed identification are known from Shoalwater Bay, Qld, southwards to Wilsons Promontory, Vic and the Furneaux Group in Bass Strait. It is farmed in Qld and NSW from native stock and in the Albany area of south-western WA from introduced stock. Reports of this species from northern Australia are incorrect as they relate to other similar looking Indo-West Pacific species, particularly the so-called Saccostrea cucullata.

Habitat: This species lives in a wide variety of habitats, from exposed rocky shores with high salinity to sheltered mangrove forests with lower and variable salinity. Individuals adhere to any solid substrate available from rocky surfaces to mangrove branches (Fig. 2), from the intertidal down to about 3 m depth. In estuaries this species forms a dense and well-defined band on the mid-shore with individuals growing on the substrate and on older shells, forming a mass that provides habitats for other marine life.

Comparison: This species is very irregular in shape and may be confused with Magallana gigas but may be separated by the presence of chomata inside the margins of the shells, at least dorsally.

Synonymy: The name Ostrea commercialis Iredale & Roughley, 1933 was used for most of the 20th century, but Anderson & Adlard (1994) showed the Australian populations to be conspecific with those of New Zealand, and the appropriate name is thus Saccostrea glomerata (A. Gould, 1850). The name Ostraea cucullata Born, 1778 has also been used, but it is a misidentification.

Remarks: Arthur Bowes Smyth, a surgeon on the First Fleet, wrote about this species in Port Jackson in 1787:

" ... they also adhere to the branches of mangrove trees. I frequently brought the branch of a tree thus loaded with oysters on board."

The Sydney Rock Oyster, which is farmed in NSW commercially, is described by NSW Department of Primary Industry (2024):

“In stick culture oyster larvae settle on tarred (and sometimes additionally cemented) hardwood sticks 1.8 metres long and 25 mm square, which are placed in areas of estuaries where settling of spat is most reliable, typically near river mouths. The sticks are then moved to low spatfall areas to reduce "overcatch" (further spatfall on growing oysters) and are grown to maturity. The process takes from 3 to 4 years with great care required in the first two years to protect the oysters from excessive heat and predators (bream, octopus and stingray). At maturity, the oysters are removed from the sticks and graded into various sizes prior to marketing.”

“In tray culture, oyster are laid on flat trays usually one metre wide and from 1.8 - 2.7 metres in length, of timber and wire or plastic construction. They have many advantages as a cultivation method as trays are more portable, easier to manage and allow precise stocking densities to encourage oysters to grow in a more uniform and marketable shape.”

The 2021 the quantity of oysters marketed in NSW was about 66 million shells, valued at $55 million.

Fig. 1: Port Jackson, NSW. (C.92652)

Fig. 2: a. Careel Bay, Pittwater, NSW (C.70498). b. Port Jackson, NSW (C.47267). c. Port Jackson, NSW (C.12002)