Elemental fingerprints of bivalve shells (Ruditapes decussatus and R. philippinarum) as natural tags to confirm their geographic origin and expose fraudulent trade practices

Abstract

Bivalves are some of the most valued and consumed seafood species worldwide. However, these organisms can represent a threat to consumers’ health, particularly species harvested from contaminated areas (e.g., historical pollution by heavy or toxins produced by phytoplankton). The elemental composition of bivalve shells generally mirrors the geochemical conditions of the habitat where these organisms have grown. As such, in this study, the geographic origin of two economically important bivalves, the grooved carpet shell ( Ruditapes decussatus ) and Manila clam ( R. philippinarum ), sourced from several locations along the NW, W and SW Iberian coast was confirmed based on the EF of their shells. Overall, random forest analyses of EF (expressed as ratios to Ca) correctly identified the site of harvest of individuals with remarkably high success rate among locations (96.3% for R. decussatus and 98.1% for R. philippinarum ). In general, the most relevant ratios for this discrimination success were the same for both species (i.e., Ba/Ca, Co/Ca, Fe/Ca and Mn/Ca). However, species-specific differences in the EF of shells could also be perceived for specimens of the two bivalve species sampled in the same location. The present findings can allow authorities to expose fraudulent practices associated with the mislabeling of geographic origin of bivalves, namely R. philippinarum , whose harvest in one of the sampled locations (Tagus estuary) is currently forbidden due to public health issues, and develop origin certification for highly valued bivalve species sourced from specific locations (such as R. decussatus from Ria Formosa). • Elemental fingerprints (EF) of bivalve shells ( Ruditapes spp.) differed spatially. • The EF of shells trace the geographic origin of R. decussatus and R. philippinarum . • The EF of shells presented species-specific variations within the same location. • Spatial variations of EF can allow origin certification and expose illegal fishing.