Temporal, spatial, and interspecific variation in geochemical signatures within fish otoliths, bivalve larval shells, and crustacean larvae

Geochemical signatures of early life stages are increasingly used to study population connectivity. This approach utilizes spatial variability in chemical signatures to predict natal or nursery origins of post-dispersal individuals by comparison with a chemical reference atlas created from individuals of known origin. To examine the relative importance of spatial, temporal, and species variation in elemental signatures, we synthesized the chemical information of otoliths, larval shells, and whole larvae from studies that employed natural geochemical signatures in San Diego County, USA between 1997 and 2009. We compared 8 elements analyzed from 4 bivalve species, 2 larval or juvenile fishes, and Stage 1 crab zoeae. Across all species, different sets of elements best discriminated among open-coast sites or within or among bays and lagoons. In mytilid mussels, which had the most complete record, all 8 elements were more variable over time than space at the site level, highlighting the need to resample the reference atlas during each study. More coarsely, however, bay and lagoon taxa maintained distinct chemical signatures both from each other and from those on the open coast, despite interannual variability. Spatially identifiable signatures for all species were likely imparted by a combination of pollution in bays and export to adjacent coastlines (copper, lead), a heterogeneous distribution of land-sourced elements (manganese, cobalt, uranium), and incorporation that may vary in response to temperature (barium, manganese, strontium) and salinity (7 elements). These results identify important elements for larval tracking of additional species depending on habitat and life history; however, source population signatures appear species-specific.