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An enriched isotope mass-marking technique for the early life-history stages of cephalopods


The natal signs of juveniles recruiting into adult populations in marine systems are invariably unknown.  Stable isotopes offer the potential to provide unique, unequivocal chemical signatures for calcified structure of fish and invertebrates at a variety of life-history stages.  Giant Australian cuttlefish (Sepia apama) eggs were immersed in water enriched in 137Ba for a range of immersion times (2, 5 and 8 days) and concentrations (0.3, 1.0 and 10μg L-1).  To test the effect of developmental stage, eggs were also immersed in 137Ba for 2 days at a range of stages prior to hatching.  Statolith isoptope ratios were measured used laser ablation inductively coupled plasma-mass spectrometry.  Ratios of 138Ba/137Ba were significantly different to controls for all 137Ba concentrations and immersion times, suggesting that this technique could provide a valuable tool for mass-marking the early life-history stage of cephalopods.  The optimal timing for marking statoliths of S.apama eggs is currently being investigated, and will provide information on whether the incorporation of 137Ba will vary with developmental stage.  Our results reinforce the value of stable isotopes as a tool for tracing movement and natal homing of fish and invertebrates.