Sydney Rock Oysters – a life under threat

The Sydney Rock Oyster (Saccostrea glomerata) is endemic to Australia and New Zealand and is a quintessential member of Australia’s aquaculture industry. But the life of Sydney Rock Oysters is under threat; increasing anthropogenic pressures on coastal ecosystems have caused wide spread losses of these commercially valuable species2,3,4. In a recent seminar by Doctor Emma Thompson at the Sydney Institute of Marine Science, in conjunction with Macquarie University, she explained her research on the threats and impacts of disease on the Sydney Rock Oyster [Figure 1].

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Figure 1: Sydney Rock Oyster, Saccostrea glomerata

A Rich History of Oysters

The Sydney Rock Oyster has been a commercially important species in Australia and in particular NSW since colonial times. Dr Thompson explains that the lime from mortar used in old Government House was in fact from the shells of ground Sydney Rock Oysters. The first oyster farm was originally set up in the Georges River back in 1872; where even today, Oyster farms still persistent on the Georges River1. Currently Sydney Rock Oysters are the largest contributor in aquaculture and account for half of Australia’s edible oyster production1. This outcome has been as a result of an exponential increase in aquaculture as well as the plateauing of marine capture rates since the 1990’s1.

Factors of Disease

For Disease to take hold of a population, a number of factors must be in place [Figure 2]. Aquaculture is especially prone to outbreaks in disease for a number of reasons; the densities of which animals are grown in aquaculture allows for an ease of transmission between viable hosts1,2. The marine environment also provides an optimal environment for disease transmission, aided by flow regimes and a stable medium2.

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Figure 2: Factors of disease

QX disease and its Implications

The QX disease; originally ‘Queensland Unknown’ (after its origin), is now described as Marteilia sydneyi is one of the potent threats facing Sydney Rock Oyster populations with mortality rates of up to 98% in some instances2. M. sydneyi is commonly found in the gut of oysters, where it is of little concern to the oyster and can be readily killed off by enzymes in the oyster’s blood cells2. It is the enzyme phenoloxidise (PO) that produces melanin, which in turn seeks out and destroys the M. sydneyi parasite2.  The fact that M. sydneyi is quite widespread in Sydney Rock Oyster populations, but QX outbreaks only occur in a number of areas provided an interesting conundrum to biologists. It was determined that a reduction of salinity was inducing an environmental stress great enough to reduce the effectiveness of PO and allow the proliferation of M. sydneyi2. The parasite prevents the oyster from feeding and also attacks the immune system. QX has had massive implications on Sydney Rock Oyster populations, the aquaculture industry and has led to the rapid propagation of the non-native Pacific Oyster Crassostrea gigas2. Pacific Oysters are fast growers and are often able to outcompete their native counterparts; the Sydney Rock Oyster. The competition by the Pacific Oyster has led to the decline of the dominance of the Sydney Rock Oyster and eventuated in a gradual ecosystem shift.

These threats coupled with economic losses led to intervention by the Department of Primary Industries (DPI); who in 1990 introduced a selective breeding program to enhance the survivorship of the Sydney Rock Oyster2. The breeding program has generated a number of highly selected for traits; producing a QX resistant oyster, a winter resistant oyster and a fast growing oyster. Today researchers such as Dr Thompson are constantly monitoring the health of Sydney Rock Oyster populations from a molecular level right through to an ecosystem level changes. Studies have observed effects of metal contamination, ocean acidification, disease and environmental stressors by comparing selectively bred oysters with wild populations2,3,4.

What the future holds

Dr Thompson explains whilst there is still a number of threats facing, the Sydney Rock Oyster’s future is secure; a recent grant with Macquarie University will lead the way for a new molecular study for the Sydney Rock Oyster, including the approval of an entirely new breeding program. This new breeding program will mean the cessation of the current breeding program that had been running for the last 20 years. The new program will create a more scientifically based selective breeding line and prevent potential inbreeding. A study is then planned to determine if this new program will impact wild Sydney Rock Oyster Populations through broadcast spawning. This research will further support the management of the Sydney Rock Oyster and continue its profitability as a key member of Australia’s aquaculture industry.

References

  1. Nell, J.A. 1993. Farming the Sydney rock oyster (Saccostrea commercialis) in Australia. Reviews in Fisheries Science, 1(2): 97-120.
  2. Raftos, D.A. & Peters, R. 2003. The role of phenoloxidase suppression in QX disease outbreaks among Sydney rock oysters (Saccostrea glomerata). Aquaculture, 223(1-4): 29-39.
  3. Parker, L., Ross, P. & O’Connor, W.A. 2009. The effect of ocean acidification and temperature on the fertilization and embryonic development of the Sydney rock oyster Saccostrea glomerata. Global Change Biology, 15(9): 2123-2136.
  4. Thompson, E.L., Taylor, D.A., Nair, S.V., Birch, G., Haynes, P.A. & Raftos, D.A. 2011. A proteomic analysis of the effects of metal contamination on Sydney Rock Oyster (Saccostrea glomerata) haemolymph. Aquatic Toxicology, 103(3-4): 241-249.

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  1. Olivia Garnett.http://www.abc.net.au/reslib/201112/r873198_8536029.jpg

6. Cody Beckley http://glenriddlemaintenance.blogspot.com.au/2010_09_01_archive.html

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