The universal imprint of oxygen isotopes can track the origins of seafood

Abstract

Identifying the source of seafood is critical for combatting seafood fraud, but current tools are predominantly developed and applied on a species-specific basis. This study investigates how multiple marine taxa could be geolocated at global scales by exploiting stable oxygen isotope compositions in carbonate biominerals (δ 18 O biomin ), where we expect to see universally expressed and predictable spatial variation in δ 18 O biomin values across taxa. We constructed global ocean isoscapes of predicted δ 18 O biomin values specific to fish (otoliths), cephalopod (statoliths) and shellfish (shells), and a fourth combined "universal" isoscape, and evaluated their capacity to derive δ 18 O biomin values among known-origin samples. High correspondence between isoscape-predicted δ 18 O biomin values and a compiled database of measured, georeferenced values (3954 datapoints encompassing 68 species) indicated that this δ 18 O biomin approach works effectively, particularly in regions with highly resolved projections of seawater δ 18 O composition. When compared to taxon-specific isoscapes, the universal isoscape demonstrated similar accuracy, indicating exciting potential for universal provenance applications. We tested the universal framework via a case study, using machinelearning models to identify sample origins amongst regions of divergent (Tropical Asia vs Temperate Australasia) and similar (Temperate Asia vs Temperate Australasia) climates and latitudes. Classification accuracy averaged 75.3% between divergent regions, and 66% between similar regions. When endothermic tuna species were excluded from the analysis, the accuracy between divergent regions increased up to 90% between divergent regions. This study presents the first empirical step towards developing universal chemical markers, which have the potential to support a more inclusive and global approach of validating provenance of seafood.

Innovation to limit seafood fraud post-COVID-19

“…Yet, soft tissue markers, based on stable isotopes, multi-element profiles, or fatty acids, remain the backbone of emerging chemical methods for seafood provenance (Cusa et al 2021 ; Fonseca et al 2022 ; Gopi et al 2019a ; Li et al 2016 ), and there are a surprisingly small number of published studies focussed on biomineralised structures, which are largely constrained to molluscs (e.g. Daryanani et al 2021 ; Mamede et al 2021 ; Ricardo et al 2015 ), with the exception of one study which focussed on multiple marine taxa (Martino et al 2022b ).…”

“…These sample stockpiles are an untapped opportunity to bypass the logistic and financial challenges of developing global geographic baseline databases or spatial reference models to verify origin claims and to underpin fisheries management and compliance throughout the supply chain. Moreover, these broad spatiotemporal archives allow researchers to determine how much isotopic and elemental signatures vary over time, which is an important consideration when using chemical markers, and is often pointed out as a drawback preventing industry uptake of chemical marker approaches (Camin et al 2016 ; Martino et al 2022b ; Reis-Santos et al 2022 ).…”

“…Ideally, in oceanic environments, we should aim to develop spatial models of chemical variation that ultimately provide maps of tracer variation and thresholds for organism assignment on a global to regional scale (Cusa et al 2021 ). This was recently achieved using oxygen isotopes in biominerals, whereby global patterns were mapped in the ocean and subsequently used to track the origins of seafood (Martino et al 2022b ). While the approach worked well across latitudinal gradients, the method needs to be combined with additional tracers to improve spatial resolution.…”

“…The implementation of provenance regulations is deficient globally, largely inconsistent across jurisdictions, and faces many challenges, including regarding labelling standards, regulations and incentives to apply provenance tools (Lindley 2021 , 2022 ). Therefore, all stakeholders and players across the supply chain will play a key role in developing a coordinated effort for method development and driving the momentum for widespread implementation (Martino et al 2022b ). Innovative approaches using tamper-proof, high throughput analyses in hard tissues, together with other approaches such as DNA and biochemical analyses (e.g.…”

Using isotopic fingerprints in gastropod shells to validate commercial production pathway and geographic provenance

“…For example, stable isotope values of oxygen (δ 18 O) in seawater, which are mediated by salinity, are primarily incorporated in equilibrium into carbonate structures with a temperaturerelated offset [9]. Furthermore, the universal expression of δ 18 O values in carbonates across different marine species has demonstrated the efficacy of δ 18 O values as a particularly useful provenance tool [10]. The stable isotope values of carbon (δ 13 C) in carbonates are also largely in equilibrium with δ 13 C of dissolved inorganic carbon of seawater, although a proportion is also related to diet and metabolic rates [11][12][13].…”