Trust your seaweeds: Fine-scale multi-elemental traceability of edible seaweed species harvested within an estuarine system

Seafood traceability is a matter of concern for producers and consumers, providing insights that can simulta-neously inform the consumers on the origin of the product, nutritional value and safety while adding market value to the products. Edible seaweed harvest has been pointed out as an environmentally friendly sustainable food production solution. Ulva spp. and Fucus vesiculosus are among the most abundant naturally occurring estuarine seaweeds with high biomass production on the Portuguese coast, making them a potentially important seafood resource. Seaweed elemental signatures chemometric analysis made it possible to confirm species authenticity with 100 % accuracy, which can be of major importance for powdered seaweed food supplements certification. Using the seaweed thallus elemental signatures through Variable Importance in Projection Partial Least-Squares Discriminant Analysis (VIP-PLS-DA) it was also possible to pinpoint the harvest location of the seaweeds with 82.5 and 92.5 % accuracy for F. vesiculosus and Ulva respectively. These same multi-elemental signatures were also able to depict the harvest season of the seaweeds (100.0 and 85.0 % accuracy for F. vesiculosus and Ulva respectively). Analysing the elements with higher importance for the PLS-DA models, it was evident that several elements with higher discriminatory ability are linked to anthropogenic sources. Considering the anthropogenic pressure gradient in the Tagus estuary, it is no surprise that these elements have a fine-scale spatial variability. While providing key models for fine-scale spatial traceability of seaweeds, the multi -elemental signatures here presented also provide key insights on their nutritional value in terms of recommended mineral daily intake, given that in some of the harvest areas analysed, seaweed thallus presented values above the maximum admissible threshold for human consumption. Thus, the developed models can be of added value for seaweed consumers, authorities and stakeholders, namely for the safe and sustainable development and monitoring of conservation and harvesting plans within estuarine systems.