The southern mud oyster, Australian flat oyster, native flat oyster, native mud oyster, or angasi oyster (Ostrea angasi), is endemic to southern Australia, ranging from Western Australia to southeast New South Wales and around Tasmania. Ostrea angasi superficially resembles Ostrea edulis and both species may be referred to with the name "flat oyster". However, the two species do not occur naturally in the same geographic distribution.
Habitat
This species is found in sheltered, silty or sand-bottomed estuaries at depths between 1 and 30 metres.
Oyster growers at Coffin Bay, South Australia have observed stingrays eating their experimental commercial stocks of Ostrea angasi.[1]
Commercial harvesting
Extensive oyster reefs in southern Australia were largely destroyed by over-exploitation during the 19th and early 20th Centuries. Oysters were dredged directly from the seabed.[2][3]
Once common, Ostrea angasi became locally extinct, in oyster-producing estuaries on the East Coast north of the Clyde River, as a result of the accidental introduction of the mud worm, Polydora websteri, from New Zealand, in 1888 to 1898. The mudworm and silting ended all sub-tidal oyster production in New South Wales and Southern Queensland, and the oyster industry there became totally dependent upon inter-tidal production of another indigenous oyster, the Sydney rock oyster, Saccostrea glomerata.[4][5]
In the 21st century, commercial oyster growers in southern Australia have started experimentally farmingO. angasi as a means to diversify their businesses. This was prompted by other growers suffering massive stock losses of Crassostrea gigas resulting from outbreaks of Pacific Oyster Mortality Syndrome (POMS).[1]
Not-for-profit projects
Port River
The not-for-profit organisation Estuary Care Foundation was established in South Australia to undertake trials growing Ostrea angasi in the Port River and adjacent waters.[6] The organisation is also involved in seagrass monitoring and restoration work within the Port River.[7][8]
It was announced, in 2023, that work would begin on re-establishing three sub-tidal oyster reefs in the Georges River estuary in New South Wales (at Audrey Bay, Coronation Bay and on the eastern side of Taren Point), and another sub-tidal reef downstream in Botany Bay. The reefs will support reintroduced Ostrea angasi—locally extinct in those waters since 1896—and also the now depleted Sydney Rock Oyster. The oyster reefs are expected to increase both water quality and biodiversity, and increase the numbers of fish.[12][13]
^Alleway, H. K. and Connell S.D. (2015): Loss of an ecological baseline through the eradication of oyster reefs from coastal ecosystems and human memory. Conservation Biology, Society for Conservation Biology. DOI: 10.1111/cobi.12452
