MEDITERRANEAN AQUACULTURE AND SUSTAINABILITY: HOLISTIC ASSESSMENT OF EUROPEAN SEA BASS (DICENTRARCHUS LABRAX) AND GILTHEAD SEA BREAM (SPARUS AURATA) FARMING

Aquaculture is one of the fastest-growing sectors globally and is increasingly recognized as a primary solution to meet the rising global demand for seafood. This trend is also present in the Mediterranean region, where two of the most important species in terms of both production and economic value are European Sea Bass (Dicentrarchus labrax) and Gilthead Sea Bream (Sparus aurata). These two species are typically farmed both in coastal sea cages and land-based systems. Both methods, while effective for large-scale production, present distinct challenges related to environmental concerns, including energy consumption, resource use, nutrient discharge, biofouling, and feed-related emissions. The central goal of this thesis is to provide a comprehensive assessment of the environmental performance of different aquaculture systems using Life Cycle Assessment (LCA) methodology. Through this approach, the thesis aims to identify key hotspots in aquaculture production, analyse potential strategies for mitigating environmental impacts, and explore innovative farming technologies such as Integrated Multi-Trophic Aquaponic systems (IMTAcs). The overarching objective is to evaluate the environmental footprint of aquaculture systems and suggest pathways for improvement, particularly by optimizing energy use, feed efficiency, and infrastructure design. A multi-criteria decision analysis (MCDA) model was also applied to a case study with the aim of providing a comprehensive sustainability assessment. This thesis is divided into three main sections each incorporating scientific studies that focus on different aspects of the environmental impact of Sea Bass and Sea Bream farming in the Mediterranean region. Chapter 3 offers an in-depth analysis of the current environmental performance of Sea Bass and Sea Bream farming, including a review of published LCA studies, comparisons between farming systems, and energy analysis. The first step of this work was to review existing LCA studies on the farming of Sea Bass and Sea Bream in the Mediterranean, summarizing and comparing the main results, identifying environmental impact hotspots, and pointing out methodological concerns. The review revealed that feed production is the most significant contributor to environmental impacts, particularly regarding greenhouse gas emissions and resource use. Additionally, most studies have employed a mass-based functional unit and "cradle-to-gate" boundary. This study also highlighted gaps in geographic representation and transparency in data reporting and underscored the need for overall sustainability assessments. Following the review, a comparison of different farming systems, including traditional sea cages and land-based systems, was performed. The results indicated that sea cage systems have lower environmental performance compared to land-based facilities, as the latter require substantial energy inputs for water pumping, filtration, and aeration. Also the energy analysis confirmed that coastal sea cages benefit from lower direct energy consumption but still face challenges related to the production of feed, which remains the dominant factor in overall environmental impacts. This chapter provides a baseline understanding of the environmental challenges associated with Mediterranean aquaculture and serves as a foundation for exploring potential mitigation strategies in the following sections. Chapter 4 focuses on two potential strategies to mitigate the environmental impact of Sea Bass and Sea Bream aquaculture. The first strategy explored is an innovative Integrated Multi-Trophic Aquaponic system (IMTAcs), which integrates fish farming with the cultivation of detritivorous filter-feeding organisms (such as mussels, clams, and polychaetes) and halophytic plants like Salicornia. The idea behind this system is to create a closed-loop where the waste from fish farming becomes a resource for other organisms in the system, thereby reducing nutrient emissions and minimizing the need for external feed inputs. The environmental performance of IMTAcs was assessed using an ex-ante LCA approach, given the experimental nature of the pilot system. Two scenarios were modelled: one using an alternative feed (composed by mussels, clams and polychaetes) and the other using traditional commercial feed. The results showed that while electricity consumption remained a major driver of environmental impacts, leading to higher environmental performance in many impact categories, IMTAcs demonstrated a strong potential to mitigate eutrophication and nutrient discharge. The integration of detritivorous and plants effectively reduced nutrient outflows compared to traditional monoculture fish farming. However, certain limitations were noted, such as the low Technology Readiness Level (TRL) of the system and the challenges in scaling up this model for commercial use. The second strategy evaluated was the use of copper alloy nets in sea cages, replacing traditional nylon or polyethylene nets. Copper alloy nets have longer lifespans and are less prone to biofouling, which reduces the need for antifouling chemicals and frequent maintenance. The environmental benefits of using copper nets were assessed, showing that their durability and recyclability could lead to some trade-offs in certain categories. However, the initial cost and recycling process remain challenges for broader adoption. Chapter 5 extends the sustainability evaluation by incorporating a multi-criteria decision analysis (MCDA) using the DEXiAQUA model. This holistic approach aims to assess not only the environmental but also the economic and social sustainability of aquaculture systems. The DEXiAQUA model was applied to a land-based Sea Bass and Sea Bream farm, providing a qualitative sustainability score that integrates these three dimensions. The MCDA revealed several trade-offs between environmental, economic, and social aspects.. The holistic evaluation emphasized the need for balanced solutions that address all three pillars of sustainability, highlighting that improvements in one area may come at the expense of another. The DEXiAQUA model proved effective in identifying key sustainability trade-offs and areas for improvement, such as optimizing feed use, enhancing energy efficiency, and improving stakeholder relationships. The findings of this thesis contribute to a deeper understanding of the sustainability challenges in Mediterranean aquaculture, particularly for Sea Bass and Sea Bream farming. The application of LCA to various farming systems has provided critical insights into the environmental hotspots of aquaculture production, with feed production being the most significant contributor to environmental impacts. While this thesis provides valuable contributions to the field of sustainable aquaculture, further research is needed to refine the methodologies and explore new technologies that can enhance sustainability. Areas for future work include the development of alternative feed ingredients, such as plant-based or insect-based proteins, which could reduce the environmental burden of feed production. Additionally, there is potential for scaling up IMTA systems and incorporating renewable energy sources into aquaculture operations, which could further mitigate environmental impacts. Ultimately, the findings of this thesis underscore the need for continuous innovation and collaboration between researchers, industry stakeholders, and policymakers to ensure the long-term sustainability of Mediterranean aquaculture.