Project number: 1996-285
Project Status:
Budget expenditure: $185,191.50
Principal Investigator: Jesmond Sammut
Organisation: UNSW Sydney
Project start/end date: 31 Dec 1996 - 22 Dec 2004


This research proposal developed from discussions with NSW and Queensland oyster growers who consider estuarine acidification is a cause of declining oyster health and productivity. A recently completed study of estuarine acidification and its role in fish kills, habitat degradation and outbreaks of EUS in estuarine fish, showed that the occurrence and duration of acidification events may be a potential threat to sessile organisms such as oysters (Sammut et al., 1996; 1996b; Callinan et al., 1996;1996b). The former study indicates that such associations between acidified water and poor oyster health are plausible. The proposed study is needed to test for putative associations between acidified water and oyster health and productivity problems. It will also generate other data that will be used to identify risk factors for QX disease. If an association between QX disease outbreaks and exposure to acidified water is confirmed, or other water quality variables are identified as causative factors, then appropriate water quality management can be developed. At present, attempts to manage acid sulfate soil drainage in NSW fail to recognise the water quality needs of oyster producers. Data from this study can be used to design acid sulfate soil management strategies to avoid secondary impacts on oyster health and maximise productivity.


1. To identify associations between water quality conditions (with particular reference to acidified water and toxic metals), other environmental factors and reduced growth rates and disease outbreaks/mortalisties in oysters at selected sites on the Hastings and Tweed Rivers.
2. To identify specific environment and management related risk factors for reduced growth rates at selected sites.
3. To identify environmental and management risk factors for specific diseases with particular reference to QX on the Tweed River.
4. To effectively communicate the findings of this study to the oyster industry and relevant agencies

Final report

ISBN: 0 7334 2086 9
Author: Jesmond Sammut
Final Report • 2017-09-29 • 5.50 MB


The study has confirmed that estuarine acidification, associated with drainage of acid sulfate soils, reduces growth rates and survival in Sydney rock oysters leading to significant production losses. The work has also demonstrated that acidification is not a factor in outbreaks of QX disease. The findings have raised greater awareness of the environmental and economic impacts of estuarine acidification, and have influenced environmental decision making at local and state government levels. The oyster industry is now recognised as an important stakeholder in the management of acid sulfate soils and their impacts. Reactive and proactive strategies to manage acidification now consider the impacts on the oyster industry whereas prior to the study the industry concerns and needs were largely ignored. The industry is now represented on key management and advisory committees responsible for management of acid sulfate soils.  The research has enabled oyster farmers to minimise stock losses through improved risk and stock management in parts of the estuary impacted by acidification. The study has provided a basis for more accurate diagnosis of acid-related oyster mortalities and important baseline information for environmental impact assessment in coastal development.

Keywords: acid sulfate soils, estuarine acidification, Sydney rock oyster, oyster mortalities, aluminium, iron, low pH.

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