Site and age discrimination using trace element fingerprints in the blue mussel, Mytilus edulis

Abstract The ability to accurately estimate population connectivity and larval dispersal among mussel populations in the Gulf of Maine is important to better understand ongoing declines in blue mussel abundances. Such efforts are crucial for crafting conservation strategies targeting important spawning and settlement sites necessary to support threatened local shellfisheries, and to mitigate the potential effects of rapid climate change on larval dispersal and survivorship. Trace element fingerprints can be used to infer larval dispersal and population connectivity, but require a reference map of geographic variation in elemental fingerprints to infer natal sites of settled mussels. Previous work has suggested rearing mussel larvae in situ to create a reference map because biomineralization differs between larval and post-metamorphic mussels, which might lead to differences in trace element fingerprints. To test whether elemental fingerprints differed between larval and juvenile (post-metamorphic) mussels (Mytilus edulis), we reared them in situ and under controlled laboratory conditions. Trace element concentrations in larval and juvenile shell matrices were quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The majority of trace element concentrations, normalized to calcium, differed between larval and juvenile mussels, resulting in elemental fingerprints that were consistently distinct between age classes. Larval and juvenile fingerprints differed consistently whether they were reared in the lab or field, probably reflecting age-specific differences in biomineralization. To use trace element fingerprints to estimate larval dispersal and population connectivity, our results suggest that a spatial map of elemental fingerprints should be created by rearing larval, not juvenile, mussels at potential source populations. Our results are consistent with what has been found for other mussels and thus may be true for all mussels, and likely true for any bivalves with age-specific differences in biomineralization.