As the global population grows, the demand for healthy and sustainable seafood increases alongside it. Aquaculture plays a crucial role in meeting this demand. But how can we ensure that this vital industry operates in an environmentally responsible manner?
Sustainable aquaculture is complex. It requires minimizing environmental impact while maximizing production efficiency. Traditional practices can lead to pollution from excess nutrients and uneaten feed. The good news is that innovative approaches like Integrated Multi-Trophic Aquaculture (IMTA) offer a solution.
A team of researchers from LEITAT Technological Center (Spain), Government of South Africa, University of Cape Town (South Africa), Marine Institute (Ireland), and Federal University of Rio Grande—FURG (Brazil) explored the potential principles incorporated in IMTA systems and existing alternatives to quantify circularity.
Circular Aquaculture: A Way Forward
The concept of a circular economy emphasizes resource efficiency and waste minimization. IMTA perfectly embodies the principles of a circular economy. By strategically combining different species at various levels of the food chain, IMTA creates a closed-loop system:
- Waste as a Resource: The waste from one species becomes a valuable resource for another. For example, filter feeders like mussels can remove excess nutrients produced by fish, reducing pollution and creating a cleaner environment.
- Enhanced Production Efficiency: IMTA optimizes resource utilization. Uneaten feed or waste products from one species are transformed into valuable nutrients for others, minimizing the dependence on external inputs.
Measuring Circularity: Bridging the Gap
While the circularity potential of IMTA is clear, quantifying its impact has been challenging due to the lack of standardized methods. The research addresses this obstacle by identifying key principles of circularity within IMTA and developing methods to measure them.
The Pillars of Circularity in IMTA
The study focuses on two fundamental principles:
- Nutrient Management: IMTA promotes efficient nutrient cycling. The waste from higher trophic level organisms (like salmon) becomes a valuable nutrient source for lower trophic level species (such as filter feeders). This reduces dependence on external inputs and minimizes pollution.
- Resource Use Efficiency: IMTA optimizes resource utilization. Water can be recirculated within the system, minimizing freshwater use. Additionally, IMTA can reduce the need for external feed inputs by utilizing waste from higher trophic levels.
Measuring Circularity: Beyond Intuition
The study goes beyond simply acknowledging the circular benefits of IMTA. The researchers propose using specific indicators to quantify its performance in circularity. These include:
- Bioremediation Indicators: Evaluate the effectiveness of IMTA systems in removing pollutants from water.
- Efficiency Indicators: Measure factors such as water recirculation, feed utilization, and energy consumption within the system. For example, the study found that IMTA systems incorporating circular ingredients (e.g., by-products from other industries) can improve feed efficiency, reducing overall resource use.
Quantifying the Benefits: Real-World Examples
The researchers evaluated IMTA trials in Ireland, Brazil, and South Africa, encompassing various combinations of fish, shrimp, and other organisms. They used specific aquaculture indicators to measure these key principles of circularity. These indicators included water recirculation rates, bioremediation efficiency (the system’s ability to remove waste), and feed, water, energy, and infrastructure material use efficiency.
The results speak for themselves:
The findings were impressive. Compared to traditional monoculture systems (rearing a single species), IMTA trials demonstrated:
- Up to a 90% increase in water recirculation, significantly reducing dependence on freshwater.
- An 80-90% improvement in bioremediation, indicating a more efficient way to manage waste and maintain a healthy ecosystem. However, the study highlights that bioremediation efficacy depends on the production scale of these “extractive” species (filter feeders and algae).
The Potential of IMTA Systems
“Our results confirmed that multi-trophic aquaculture systems operate in accordance with the circular attributes included in the essential definition of bioremediation,” conclude the scientists.
The study’s results highlight the significant potential of IMTA to promote circularity in aquaculture. By fostering a more balanced ecosystem and minimizing waste, IMTA can contribute to a more sustainable and responsible fishing industry.
The study also acknowledges limitations in the accuracy of current methods for calculating bioremediation efficiency. More research is needed to develop more precise approaches, such as stable isotope studies to trace the origin of nutrients and confirm bioremediation by extractive species.
The research was funded by the ASTRAL Project—H2020.
Reference (open access)
Checa, D., Macey, B. M., Bolton, J. J., Cardozo, A., Poersch, L. H., & Sánchez, I. (2024). Circularity Assessment in Aquaculture: The Case of Integrated Multi-Trophic Aquaculture (IMTA) Systems. Fishes, 9(5), 165. https://doi.org/10.3390/fishes9050165
