Characterizing natal source population signatures in the diadromous fish Galaxias maculatus, using embryonic otolith chemistry

One of the greatest empirical challenges in studies of marine metapopulations is assessing the role of connectivity in maintaining local populations. The use of natural tags in body structures such as otoliths has led to significant improvements in our understanding of dispersal dynamics; however, the real knowledge gap remains our ability to identify the origins of dispersing larvae. In the present study we show that embryonic otoliths of a diadromous fish native to southeastern Australia, Galaxias maculatus, can be used to quantify unique natal elemental signatures and identify potential source populations spread out along a contiguous coastline. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), we analysed embryonic otoliths from G. maculatus hatchlings from 10 rivers across coastal Victoria, Australia. We found significant differences among rivers in the concentrations of all 8 elements analysed (B, Mg, Mn, Zn, Cu, Sr, Ba, Pb). More importantly, significant differences among rivers in the multi-element signature of hatchling otoliths indicate that sites separated by 10s to 100s of km can be discriminated with a high degree of confidence. Our results show that these methods can be successfully applied to examine questions of population connectivity within metapopulations of diadromous species.