Introduction
Integrated multi-trophic aquaculture (IMTA) is a sustainable production system that promotes nutrient recycling to minimise the accumulation and discharge of waste (Chopin et al., 2012). BLUEBOOST aims to promote the adoption of technologies based on the co-cultivation of low-trophic-level species with established fed species by providing knowledge on IMTA culture technologies and the systems environmental and economic benefits. In addition, IMTA offer potential for seafood production and ecosystem regeneration in environments that are under threat from climate change and anthropogenic pressures. The Ebro Delta, in common with many sea-level coastal areas, is under threat from climate change and land has become salinised due to reduced sediment discharge from the river, sea-level rise and storm intensification. Although IMTA systems have great potential for more sustainable aquaculture and ecosystem restoration, their application by the aquaculture sector remains limited by technical complexity and the scarcity of data to demonstrate the environmental and economic benefits (Ghosh et al., 2025). This work presents the results of a trial developed in Spain, in coastal ponds of the Ebro Delta. The experiment aims to compare a monoculture system with an IMTA system that can be positioned on salinised land to provide protection from climate change-influenced coastal processes.
Materials and Methods
The study was conducted in IRTA, La R��pita Centre (Catalonia, Spain), between November 14, 2024, and October 20, 2025. Three coastal ponds of 100 m3 and 1 m depth, located in the Ebro Delta, were used. Seawater was pumped from the bay into a covered reservoir and pumped to the ponds without prior treatment. A venturi on the water inlet pipe maintained high oxygen levels close to the inlet point. A single monoculture pond was compared to two IMTA ponds. Each pond was stocked with 437 flathead grey mullet (Mugil cephalus) (53.9 ± 32.0 g weight) that were obtained from IRTA's own production. Each IMTA pond was also stocked with 1000 European flat oyster (Ostrea edulis) (15.1 ± 2.5 mm) obtained from The Oyster Restoration Company (TORC, Scotland), 1000 Pacific oyster (Magallana gigas) (15.4 ± 2.3 mm) obtained from Musclarium (Catalonia, Spain), 3161 Manila clam (Ruditapes philippinarum) (18.7 ± 1.1 mm) obtained from Proameixa Acuicultura (Galicia, Spain), and Ulva sp. (25 kg) from IRTA's own production. The mullet were fed ad libitum with a commercial feed (DIBAQ CATFISH 42, 4.0 mm). Daily mortalities were recorded, and biometric sampling was conducted every three months. Samples were also taken for nitrogen, phosphorus, and carbon analysis. Temperature was measured with sensors in the water column and sediment (HOBO, USA). Dissolved oxygen was measured twice daily, and pH and salinity once daily using a ProQuatro multiparameter meter (YSI, OH, USA). Inflow and outflow water samples were taken twice weekly to determine in vivo chlorophyll by fluorimetry, and every two weeks for nutrient analysis.
Results and Discussion
During the trial, environmental conditions ranged from 9 to 31 °C, dissolved oxygen from 2 to 10 mg/L, pH from 5.80 to 9, salinity from 26 to 38 ppt, and in vivo chlorophyll levels from 0.3 to 8 mg/L in the inlet water and from 0.3 to 14.3 mg/L in the outlet water. On October 12, 2025, a torrential rainfall event exceeding 300 L/m2 occurred, causing a sharp decrease in salinity and significantly impacting the final survival of the bivalves. Mullet reached final weights of 342.25 ± 116.20 g and 354.83 ± 165.23 g in the IMTA ponds, and 401.30 ± 148.19 g in the monoculture. Although growth was slightly higher in monoculture, survival was greater in IMTA (65.8% and 69.0%) than in monoculture (50.9%). The proportion of survivors showed significant differences between each IMTA pond and the monoculture (chi-square test; p < 0.0001 in both cases), with no differences between the two IMTA ponds. The greater final weight in monoculture could be related to a lower final density due to mortality, while all three ponds reached a similar final biomass. The Pacific oyster reached 52.94 ± 12.82 mm and 47.83 ± 8.86 mm in length, with survival rates of 86.1% and 92.1% until August, respectively, but final mortality was 100% after the rain event. The European flat oyster showed slower growth (34.15 ± 8.94 mm and 26.17 ± 9.33 mm) and low final survival (2.3% and 2.1%) with mortalities associated with high summer temperatures. The Manila clam reached a large market size of 35.55 ± 2.22 mm and 33.93 ± 1.67 mm. Clam survival of 80% and 92% were recorded in August. However, the final survival rate was 22.2% and 33.5%. During final sampling, there was no difference in the average shell size between live and dead clams, suggesting that much of the mortality occurred shortly before the final sampling (20 Oct.) that followed the torrential rain event (12 Oct.). These results point to the clam as the most promising species in the system with growth to harvest size in a short growing period and potentially high survival. Mullet also grew well and demonstrated robustness to extreme changes in the environment, both salinity and temperature. Ulva sp. showed increases of 53% and 281% in a six-week cycle, although optimisation of its support and harvesting will be necessary. Overall, the results support the potential of the evaluated IMTA system. The species appear to interact positively, which needs to be confirmed by analysis of nutrient flows through the system. The system can also give economic use to abandoned salinised land to support ecosystem restoration.
Acknowledgment
This work was funded by BLUEBOOST (SBEP2023-725), a project co-financed by the European Union through the Sustainable Blue Economy Partnership and the Agencia Estatal de Investigaci��n (AEI, Spain) (PCI2024-153525). Sandra Salcedo has been supported by an FPI grant associated to the project ECOMUGIL (RTA2021-126070OR-100) and funded by Agencia Estatal de Investigaci��n (AEI, Spain).
References
Chopin, T., Cooper, J. A., Reid, G., Cross, S., & Moore, C. (2012). Open-water integrated multi-trophic aquaculture: Environmental biomitigation and economic diversification of fed aquaculture by extractive aquaculture. Reviews in Aquaculture, 4(4), 209–220.
Ghosh, A. K., Hasanuzzaman, A. F. Md., Islam, S. S., Sarower, Md. G., Mistry, S. K., Arafat, S. T., & Huq, K. A. (2025). Integrated multi-trophic aquaculture (IMTA): Enhancing growth, production, immunological responses, and environmental management in aquaculture. Aquaculture International, 33(5), 336.