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Feasibility of shellfish reef restoration in a south-western Australian estuary

Peck, Lauren (2019) Feasibility of shellfish reef restoration in a south-western Australian estuary. Honours thesis, Murdoch University.

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With 85% of oyster reefs lost around the world within the last 130 years, these reefs are now one of the most threatened marine habitats in the world and in Australia less than 10% of naturally occurring oyster reefs remain. Shellfish reefs provide a range of services that promote healthy ecosystems, including water filtration, fish production and shoreline erosion. In estuaries, these services are extremely important as human activities are increasing degrading these environments. Thus, shellfish reefs can aid in restoring ecosystem functioning of an estuary while providing additional ecosystem services. The aim of this study was to determine the feasibility of a number of shellfish reef options for the Peel-Harvey Estuary in south-western Australia. This first involved exploring the historical and current distributions of shellfish to elucidate whether shellfish reefs existed in the Peel-Harvey Estuary and to identify a suite of candidate species.

A bioclimatic modelling approach was then used to elucidate the suitability of five native Australian oyster species to the environmental conditions that occur in the Peel-Harvey Estuary, the largest estuary in south-western Australia. Laboratory tank trials were then used to validate the results of that model, in which the two most suitable species, i.e. Ostrea angasi and Saccostrea glomerata, were exposed, for two months, to the extremes in water temperature and salinity that occur in the Peel-Harvey Estuary during summer (26◦C and 48ppt) and winter (15◦C and 14ppt) and their survival, body condition index (BCI) and behaviour (valve activity) monitored.

The probability of survival (S) over the duration of the study was lowest for O. angasi in the summer (S=0.0) and winter treatments (S=0.18), which both differed significantly (P<0.001) from the control group (marine condition), and were consistent with the salinity in the winter and summer treatments falling outside previously recorded tolerance thresholds. In contrast, S. glomerata had a high probability of survival in winter (S=0.98), and ~50% survived the extreme summer conditions. A significant difference of valve activity was found for O. angasi between the three conditions (P<0.05), however, only a significant difference in valve activity for S. glomerata was found between the marine and summer (P<0.05), and marine and winter conditions (P<0.05). Overall, body condition index (BCI) did not differ significantly (P>0.05) before or among treatments. The results of the bioclimatic model and survival analyses suggest that S. glomerata was the most suitable candidate for shellfish reef restoration in the Peel-Harvey Estuary, given in particular the extremes that occur in salinity. Further work is required to determine the most suitable areas in the estuary that would maximise survival and growth and thus where such reefs would have a positive impact on the overall health and resilience of the Peel-Harvey Estuary.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
United Nations SDGs: Goal 14: Life Below Water
Supervisor(s): Cottingham, Alan and Tweedley, James
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