Elemental uptake via immersion: a mass-marking technique for the early life-history stages of cephalopods

Despite the ecological and increasing commercial significance of cephalopods worldwide, little attention has been paid to developing techniques that investigate the movement of early life-history stages. We evaluated the potential of mass-marking giant Australian cuttlefish Sepia apama hatchlings, via immersion of eggs in water enriched in 137Ba isotope. Eggs were immersed in several 137Ba concentrations, for varying durations, and at different stages of development. Statoliths of hatchlings from each combination of 137Ba concentration (0.3 and 1 μg l–1) and immersion time (2, 5 and 8 d) produced lower mean 138Ba:137Ba values than control hatchlings, and mark success was generally high (70–100% of statoliths were unequivocally marked across all treatments). Development stage was an important factor, with statoliths successfully marked only for eggs immersed in 137Ba at 10 wk of age. These results suggest that marking of statoliths via enriched isotope immersion offers considerable potential for understanding juvenile dispersal and connectivity of cephalopod populations in nature.