Integrating microbial community dynamics into life cycle assessment: towards a microbial dimension of aquaculture...

Aquaculture is a cornerstone of Mediterranean seafood production; however, its comprehensive environmental footprint, specifically its impact on microbial community dynamics, remains insufficiently assessed. Conventional life cycle assessment (LCA) frameworks primarily focus on resource use and emissions along the supply chain, largely overlooking microbiological responses that may signal ecological degradation or legacy effects. This represents a limitation for sustainability assessment, as microbial community shifts can influence ecosystem functioning and environmental health. The aim of this study is to evaluate whether microbial community indicators can provide complementary insights to conventional LCA metrics in marine aquaculture systems in an exploratory manner. This study presents an integrated assessment of a marine finfish aquaculture system in Krifo Limani, Greece, combining LCA, nutrient-balance modelling, and microbial community analysis across three sampling locations. Environmental impacts were quantified using ReCiPe 2016 midpoint indicators based on primary data, using a functional unit of 1 kg of live fish at the farm gate. Nutrient-balance modelling estimated nitrogen (N) and phosphorus (P) release based on feed composition and whole-fish nutrient retention, and 16S rRNA gene sequencing was employed to assess shifts in water-column and sediment bacterial communities associated with aquaculture activity. This study represents an early attempt to integrate microbial community dynamics into LCA-based environmental assessment of aquaculture systems. Across all 18 impact categories, the active farm exhibited significantly lower impacts per unit of production compared to the inactive farm, with reductions of 30-40% in climate change, eutrophication, toxicity, ecotoxicity, resource depletion, and water consumption. These improvements reflect increased operational efficiency, particularly regarding feed conversion and energy use. Despite modelled differences in nutrient emissions, dissolved inorganic nutrient concentrations in surface waters remained consistently low and comparable to the control site. In contrast, microbial communities exhibited more distinct responses under the conditions sampled. Taxa commonly associated with pathogenicity or organic enrichment, such as Vibrio, Photobacterium, Sulfurovum, Desulfopila, and Desulfocapsa, were enriched at farm sites. These microbial signatures persisted in the sediments of the inactive farm long after production had ceased, suggesting a potential legacy effect. The findings suggest the potential value of integrating microbial metrics into aquaculture sustainability assessments. We explore the concept of "microbial marine toxicity" as a potential complementary impact dimension. This concept is proposed as a preliminary and conceptual framework rather than a fully established impact category, which requires further methodological development. However, the results are based on a single sampling campaign and should be interpreted as exploratory. This approach may contribute to the development of more comprehensive and ecologically relevant sustainability assessment frameworks for aquaculture.