Introduction
Integrated Multitrophic Aquaculture (IMTA) has been assumed to be more sustainable than monoculture of aquatic species, but wider adoption by the industry has not yet taken off. The BLUEBOOST project investigates the extent to which adding species to monoculture systems is technically feasible, scalable and economically and environmentally more sustainable in six case studies. Here we present preliminary results of three of these case studies. The first case (Poland) is a freshwater IMTA system combining commercial carp pond farming (Cyprinus carpio) with crayfish (Pontastacus leptodactylus) and watercress (Nasturtium officinale) cultivation. The second case (Italy) is commercial offshore mariculture (Sparus aurata, Dincentrarchus labrax, and Argyrosomus. regius) with the integration of flat oyster (Ostrea edulis) lantern farming. The third case (Brazil) is a RAS-IMTA system integrating biofloc shrimp monoculture (Penaeus vannamei) with oysters (Crassostrea gazar), sea cucumbers (Holothuria grisea), mullets (Mugil liza), and Salicornia nei.
Methods
Data on production and use of energy and materials, generation of waste and emissions was collected from the three case studies through site visits, and through online meetings and communication before and after the visits. Life Cycle Assessment methodology was used following a pre-defined scheme (Ziegler et al. 2024), e.g. using the functional unit 1 tonne of (mixed) biomass with an economic value and applying mass-based allocation between co-products where needed. Nutrient retention potential was assessed by quantifying the fraction of N and P retained in biomass harvested from the system relative to those released by fed species and carbon deposited and released. Basic discounted cash flow analysis was used to assess the private profitability of the proposed IMTA systems compared to the established monoculture equivalents.
Results and discussion
Important drivers of Polish carp farming were the amount of feed used per tonne of fish, which was more important than feed composition. In some years, fish were fed only grains, in others, a combination of grains and compound feed. The incremental IMTA investment is financially worthwhile due to the additional income from crayfish and watercress that can be achieved with moderate additional inputs in the form of infrastructure (crayfish cages) and labour. Still, emissions were not affected due to the small volume of additional species (a few kilos) in relation to the volume of carp harvested (25 tonnes). Also in farming of marine finfish (European seabass, gilthead seabream, and meagre) off Sardinia , environmental impacts are driven by feed use. In the IMTA setup, with the addition of European flat oyster farming, emissions remain almost unchanged, again due to the low volume of oysters farmed (96 kg liveweight oysters vs 376 tonnes of finfish). The IMTA investment is profitable, since oysters can be farmed without the use of extra feed and using relatively low-cost gear and the species added has a high economic and cultural value for which consumers may be willing to pay a premium compared to established non-native oyster species (Magallana gigas, Pacific cupped oyster). In the Brazilian case, emissions from shrimp monoculture were mainly driven by energy use of the recirculating system which was only moderately lowered by the addition of mullet, oysters, sea cucumbers and edible salt marsh plants (Salicornia sp.), again due to the low volumes of these species farmed. Although they did not require any additional feed or energy inputs, only some farming infrastructure, containers for keeping them and tubing to pump the water, the extra outputs were too small to affect the environmental assessment of the system. Whether the sales of outputs from an up-scaled IMTA operation are enough to justify the IMTA investment is still subject to inquiry.
Conclusions
Preliminary results from the case studies confirm findings from the literature about IMTA, that the environmental benefits are small and that the main improvement potential is financial. For IMTA to deliver larger environmental benefits, the systems need to be scaled up so that volumes of co-farmed species match. As a next step of BLUEBOOST, theoretically scaled up production will be modelled, both from an environmental and economic perspective, and three more case studies will follow- in Spain, Portugal and Brazil.
Acknowledgment
This study was funded by the Sustainable Blue Economy Partnership (SBEP) project BLUEBOOST ID: SBEP2023-725 with European Union COFUND, Horizon Europe and, Formas (Grant 2023-02266) for Sweden, Ministero dell'Universit�� e della Ricerca for Italy.
References
Ziegler et al. (2024) BlueBoost Deliverable 12. Internal report specifying the LCA methodology applied in the BlueBoost project. Can be shared upon request to: friederike.ziegler@ri.se