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Ostrea angasi (Family Ostreidae)

Oyster, Southern Mud Oyster

Distribution:

The Southern Mud Oyster ranges from NSW, around southern shore including Vic, Tas, and SA to Fremantle, WA (NSW, VIC, TAS, SA, WA).

Features:

The Southern Mud Oyster is a triangular to round-shaped bivalve, with two unequal-shaped valves. The upper valve is thick, heavy, rounded but compressed, being flat to concave and is sculptured with irregular, scaly, concentric growth-scales called lamellae that often form a fluted (wavy) shell margin. The upper valve fits into the lower valve. The lower, attached valve is flat and cup-shaped. It grows to a length of 100-180mm. The shell colour is ash-grey to off-white and is usually darker towards the hinge area. Inside the shell is white.

Ecology/Way of Life:

The Southern Mud Oyster occurs at and below low tide level attached to stones and shells, or free living in muddy areas. They prefer a habitat on low to medium energy coasts. Younger oysters are attached to stones, boulders and shells, but larger older ones, about six years old, may be free-living in muddy areas. The Southern Mud Oyster was an important food for pre-European Aborigines and shell remains a common component of many coastal middens. Bennett & Dakin describe how this oyster must have once been common near Sydney judging the volume of remains in Sydney Aboriginal middens. The Southern Mud Oyster is marketed for eating on southern Australian shores.

O'Sullivan (1980) has described the fertility, breeding season and incubation period of the Southern Mud Oyster, and Dix (1980) detailed its culture. The Southern Mud Oyster retains its eggs within its body after they have been fertilised and they are not released until after having developed to their first stage.

Interaction with Humans/Threats:

The Southern Mud Oyster is abundant in some localities, and is marketed in large quantities, but uncommon in others, depending upon the habitat. In the late 19th C. dredge fisheries for the Southern Mud Oyster operated in Port Phillip Bay, Vic, and at Coffin Bay and Stansbury, SA. However, the population crashed, possibly caused by a parasitic protozoan Bonamia sp. (Edgar). The Southern Mud Oyster is beginning to be cultivated in shellfish farms. The future of this species and especially its suitability for mariculture needs to be researched.

Other Comments:

Ostrea angasi is named after George Fife Angas, an important businessman associated with the early foundation and prosperity of South Australia.

Further Reading:

Bennett, I. (1987). W. J. Dakin's classic study: Australian Seashores: a guide to the temperate shores for the beach-lover, the naturalist, the shore-fisherman and the student. p.321, Angus & Robertson.

Davey, K. (1998) A Photographic Guide to Seashore Life of Australia. p.125, New Holland Press, Sydney.

Dix, T.G. (1980). Growth of the native oyster Ostrea angasi using raft culture in Tasmania, Australia. Aquaculture, v.19(2), 109-115.

Edgar, G.J. (1997). Australian Marine Life: the plants and animals of temperate waters. p.294, Reed.

Jansen, P. (2000), Seashells of South-East Australia. p.80, Capricornia Publications.

Jones, D. & Morgan, G. (1994). A Field Guide to Crustaceans of Australian waters. Reed.

Macpherson, J.H. & Gabriel, C.J. (1962). Marine Molluscs of Victoria. p.311, Melbourne University Press.

Marine Research Group of Victoria (1984). Coastal Invertebtrates of Victoria: An atlas of selected species. p. 86, Museum of Victoria.

O'Sullivan, B.W. (1980). The fertility of the Port Lincoln Oyster (Ostrea angasi Sowerby) from west Lakes, South Australia. Aquaculture, v.19, 1-11.

Shepherd, S.A. & Thomas, I.M. (1989). Marine Invertebrates of Southern Australia. Pt. II. p.649, South Australian Govt. Printing.

Wells, F.E. & Bryce, C.W. (1988). Seashells of Western Australia. p.162, Western Australian Museum.

Acknowledgments:

Text, map & photograph by Keith Davey.

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