There has been a continuous decline in both the production and general performance of the
SRO in NSW estuaries over the past three decades. The relationship of this decline to both
environmental and oyster-density related factors are assessed in this thesis. This question has
been examined at different scales: a large scale that compares two different estuaries (Clyde and
Shoalhaven Rivers, southern NSW); a regional scale that encompasses variations within an
estuary and, at a lease scale that examines processes pertaining to individual or small groups of
oysters. Levels of inorganic nutrients were in general very low potentially limiting primary
production. The limiting nutrient was nitrogen or phosphorus depending on whether long term
conditions were dry or wet, respectively. Only during rain events, through the input of terrestrial
material, were conditions favourable for fast rates of primary production. Carbon and nitrogen
isotope analysis has demonstrated that both external material and local resuspension of the
benthos constitute a major proportion of the SRO diet. The uptake of the various food sources
also varied considerably depending on local environmental conditions. Increases in SRO growth
were strongly correlated to increases in temperature with a low temperature cut-off at ~13°C.
Growth also appeared to reduce considerably when salinities lower than ~15ppt persisted for the
order of a month. These factors may alter growth through changes in filtration rates. These
processes were modelled in a coupled hydrodynamic-NPO (Nitrogen-Phytoplankton-Oyster)
model of the Clyde River. This demonstrated that primary production was more affected by
estuarine dynamics and nutrient concentrations than oyster uptake. At the current levels of
oyster densities, primary production by itself could not account for the observed oyster growth,
however growth became realistic with observed levels of POC added to the model. A set of
environmental indices were used to complement the model and to assess the sustainability of the
culture system. The combined indices indicated that while the ecological carrying capacity of
the Clyde was exceeded the production capacity at an estuarine scale was not. On the lease
scale, density experiments showed that while growth was not reduced as a result of current
stocking densities, the condition index was significantly affected.
| Identifer | oai:union.ndltd.org:ADTP/204527 |
| Date | January 2008 |
| Creators | Rubio Zuazo, Ana Maria, anarubio.zuazo@gmail.com |
| Publisher | The Australian National University. Centre for Resource and Environmental Studies |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.anu.edu.au/legal/copyrit.html), Copyright Ana Maria Rubio Zuazo |
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