Introduction
As global fish consumption increases due to population growth, aquaculture has become a critical component of future seafood supply, particularly as yields from capture fisheries stagnate or decline. Aquaculture contributes to food security and economic development but also raises environmental concerns, including organic enrichment, eutrophication, habitat alteration, biodiversity changes, and the potential transmission of pathogens to wild populations.
Material and Methods
Here, we evaluate the potential environmental impacts of a recently deployed offshore Atlantic bluefin tuna (Thunnus thynnus) fattening facility located off the Basque coast in the Bay of Biscay. The facility forms part of an innovative pilot project led by the Balfegó Group in collaboration with AZTI, representing one of the first applications of capturebased tuna aquaculture under exposed Northeast Atlantic conditions.
To assess impacts on both the benthic compartment and the water column, we combined environmental DNA (eDNA) metabarcoding, hydrodynamic particletracking modelling, and multivariate statistical analyses. Vertical and horizontal patterns in microbial and microbenthic community structure were compared between reference sites and sites located at increasing proximity to the farming facility.
Compared with traditional biomonitoring approaches based on visual identification of macrobenthic assemblages, eDNAbased techniques offer several advantages, including improved detection of meiofauna and microorganisms, early life stages, and cryptic taxa, as well as greater costeffectiveness and spatial resolution.
Implications
The results of this study evaluate the effectiveness of modern molecular tools for detecting and characterizing environmental interactions associated with offshore tuna aquaculture, building on approaches previously validated for salmon farming in nearshore systems of northern Europe. Ultimately, this work provides novel insights into ecosystem responses to highvalue seafood production systems and contributes to understanding the resilience of offshore marine ecosystems under aquaculturerelated pressures.