Variability of Stable Isotope Ratios of Glassfish (Ambassis jacksoniensis) from Mangrove/Saltmarsh Environments in Southeast Australia and Implications for Choosing Sample Size

Abstract

Stable isotopes offer an accurate and cost-effective way to understand critical pathways of energy, and their use has application where aquatic habitats have been degraded. Isotope ratios can offer insights into appropriate conservation and rehabilitation techniques to manage these valuable resources. To date, the literature shows little attention to spatial and temporal variation in isotope signatures of samples taken from estuarine environments. This study reports on an investigation of sample size by which to determine isotopic signatures within a single species of fish, Ambassis jacksoniensis. Provided are two ways by which to determine how many samples are needed, and the results imply that care may be needed in interpreting previous studies based on small sample size. A minimum of five individuals would appear necessary in some cases.

Keywords:

• stable isotopes
• carbon
• nitrogen
• sample size
• food webs

Acknowledgements

The authors acknowledge Mr. Alan Williams for assisting with stable isotope sample analysis, and for the valuable comments and encouragement by Dr. Suzanne Hollins and Mr. John Twining of the Institute for Environmental Research, Australian Nuclear Science and Technology Organisation (ANSTO). We thank the Australian Catholic University for providing sampling nets, and the Sydney Olympic Park Authority, National Parks and Wildlife Services of the Department of Environment and Climate Change, which provided access to the sites. Animal ethics approval was granted by the Director General's Animal Ethics Committee of the Department of Agriculture, project number 02/3477. Fish samples were collected under Scientific Collection Permit P06/0005.