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Integrated multi-trophic aquaculture: a sustainable approach to production

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By Milthon Lujan

Example of Integrated Multi-trophic Aquaculture (IMTA) in open sea. Source: Lothmann et al., (2022).
Example of Integrated Multi-trophic Aquaculture (IMTA) in open sea. Source: Lothmann et al., (2022).

By: Milthon B. Lujan Monja and Carmen Chimbor Mejia

Traditional aquaculture faces challenges such as resource overexploitation, environmental pollution, and food security. In this context, Integrated Multitrophic Aquaculture (IMTA) emerges as an innovative and sustainable alternative for food production.

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Current monoculture practices and intrinsic perceptions within the aquaculture industry have shifted towards an expansion of carnivorous species production with lower trophic level organisms in ecologically balanced aquaculture farms (Neori, 2008). In this regard, cultivation approaches must be implemented to ensure the sustainability of the aquaculture industry.

In this context, Integrated Multitrophic Aquaculture (IMTA) arises as the answer to reduce the negative environmental impacts of aquaculture systems concentrated on a single species.

What is Integrated Multi-trophic Aquaculture (IMTA)?

IMTA mimics natural marine and freshwater ecosystems by combining the cultivation of different species from different trophic levels within the same system. Integrated multitrophic aquaculture systems are a type of polyculture. For example, fish, shellfish, and algae can be cultivated together, so that the waste from one species becomes food or fertilizer for others.

Chopin (2006) defines Integrated Multitrophic Aquaculture (IMTA) as the cultivation of organisms that require exogenous food (fish or shrimp) in combination with organisms that extract dissolved inorganic nutrients (macroalgae) or particulate organic material (bivalve mollusks), and biological and chemical processes are balanced; in other words, IMTA can be defined as the cultivation of multiple organisms from different trophic levels simultaneously, to create a balanced system.

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According to Knowler et al., (2020), in integrated multitrophic aquaculture (IMTA), species from different trophic levels are raised in proximity to each other, and the co-products (organic and inorganic waste) of one cultivated species are recycled to serve as nutritional inputs for others.

As examples of IMTA, we can cite the cultivation of salmon, mussels, and macroalgae, where salmon is the main crop, and mussels and macroalgae are used to utilize organic waste (unconsumed feed) and inorganic waste (nitrogen and phosphorus) from the decomposition of feces and unconsumed feed.

The concept of integrated multitrophic aquaculture is extremely flexible and can be applied to cultivation systems using freshwater or marine water. The important thing is that organisms are selected based on the functions they have in the ecosystem and their economic value or potential (Chopin, 2006, and Neori, 2008). Currently, there is a trend to include aquaponics, biofloc, and symbiotic as types of IMTA systems.

Advantages of Integrated Multitrophic Aquaculture

IMTA systems offer a series of benefits for aquaculturists and the ecosystem. Correia et al., (2020) highlight that the concept of IMTA was developed as a way to increase the sustainability of intensive aquaculture systems, using an ecosystem-based approach. Thus, the main benefits of aquaculture include:

Reduction of negative environmental impacts of aquaculture

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IMTA systems can reduce ecological impacts near aquaculture operations, improve social perceptions of aquaculture, and provide financial benefits for aquaculture producers through product diversification, faster production cycles, and price premiums on Integrated Multitrophic Aquaculture products (Knowler et al., 2020).

Likewise, Integrated Multitrophic Aquaculture has the potential to increase the sustainability of aquaculture worldwide, as it can help reduce eutrophication in freshwater and marine ecosystems; in this regard, Chopin et al. (2010) indicate that IMTA systems not only produce valuable biomass but also provide the service of nutrient reduction.

Regarding this, Nederlof et al., (2022), based on the eco-physiological requirements of cultivated species, as well as the response of “extractive” species to waste from “fed” species, defined the maximum retention efficiency for a conceptual marine IMTA system of four species (fish, algae, and bivalves) and demonstrated that theoretically between 79% and 94% of nitrogen, phosphorus, and carbon supplied with fish feed could be retained.

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On the other hand, Chary et al., (2020) propose a methodology that can be a powerful tool for predicting the magnitude of environmental benefits that can be expected from IMTA production systems and for showing the possible transfer of impact between spatial scales.

Nutrient retention

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Another advantage offered by integrated multitrophic aquaculture systems to aquaculturists is the retention of nutrients that are not utilized by fed species. Regarding this, Nederlof et al., (2022) reported that IMTA systems have nutrient retention efficiencies ranging from 45% to 75% for closed systems and from 40% to 50% for open systems. In this way, IMTA also fits into circular economy approaches. In the same vein, Jerónimo et al., (2021) demonstrated that it is possible to produce biomass of polychaetes (Hediste diversicolor and Terebella lapidaria) with high nutritional value through an eco-design concept like integrated multitrophic aquaculture (IMTA).

Diversification of aquaculture production

IMTA allows the cultivation of a variety of species, reducing the risk associated with dependence on a single species. Thus, Integrated Multitrophic Aquaculture provides the opportunity to diversify and reduce economic risk when appropriate species are chosen.

Nissar et al., (2023) emphasize that IMTA offers a sustainable approach to aquaculture development with a two-component population configuration: fed aquaculture species (fish or shrimp) and extractive species (algae, mollusks, echinoderms, etc.). Meanwhile, Magondu et al., (2022) designed an integrated multitrophic aquaculture system using marine shrimp (Penaeus indicus) integrated with sea cucumbers (Holothuria scabra) and cockles (Anadara antiquata), concluding that IMTA can lead to better utilization of pond communities to further enhance pond productivity.

Mitigation of Climate Change Effects

Hamilton et al., (2022) evaluated the potential of Integrated Multitrophic Aquaculture (IMTA) to mitigate the impact of ocean acidification on mollusk growth; they worked with abalone (Haliotis rufescens) and red algae dulse (Devaleraea mollis), and concluded that IMTA will buffer abalone commercial operations against the effects of ocean acidification during vulnerable early life stages.

Improvement of Aquaculture Productivity

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Omont et al., (2020) suggest that the integrated multi-trophic aquaculture system (whiteleg shrimp and Pacific oyster) imposes changes in the digestive microbiome dynamics that could improve water management and shrimp productivity. Meanwhile, Lal et al., (2023) conclude that integrated multitrophic systems promote economic and environmental sustainability by converting by-products and unconsumed feed from fed organisms into harvestable crops, thereby reducing and increasing economic diversification.

Barriers to Commercial Adoption of Integrated Multitrophic Aquaculture

For integrated multitrophic aquaculture to become a commercially viable option, it still needs to overcome some challenges. Sickander and Filgueira (2022) report that the main challenges for commercial implementation of IMTA are:

  • Economic issues related to capital and maintenance costs constitute bottlenecks for implementation.
  • Lack of governmental support and commitment to implementation and innovation were repeatedly mentioned among literature review documents and industry surveys.
  • Despite speculations about its viability, the fact that integrated multi-trophic aquaculture is not commonly implemented at a commercial scale constitutes a barrier to industry adoption.

Rosa et al., (2020) describe a lack of legislation to understand the co-cultivation of multiple species in proximity; and existing maximum residue limits for fish should be established for other organisms also produced in integrated multitrophic aquaculture systems to protect consumer health.

Some IMTA System Experiences

In the last decade, a series of integrated multi-trophic aquaculture researches with different species have been developed worldwide. Experiments have been conducted with macroalgae, polychaetes, sponges, marine fish, among others.

Likewise, IMTA systems can be implemented in open systems (cages) or closed systems (RAS, ponds), and include species variations such as fish/algae, fish/bivalves, terrestrial plants/fish, among others.

IMTA with Cage Culture System

Integrated multitrophic aquaculture systems are designed to mitigate environmental problems caused by aquaculture. Abreu et al. (2009) report the cultivation of Gracilaria chilensis near salmon farms, determining that macroalgae growth was higher in suspended cultures near salmon cages, concluding that 100 ha of suspended G. chilensis cultivation can effectively reduce nitrogen input from a 1500 t salmon farm.

Cutajar et al., (2022) evaluated the use of sea cucumber Holothuria poli in fish cage culture in the Mediterranean Sea, concluding that sea cucumber could have the potential to absorb organic waste from culture and increase aquaculture production, albeit with important considerations for facility design and population density.

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On the other hand, Jerónimo et al., (2021) studied the fatty acid profile of four polychaete species and concluded that it is possible to produce biomass of these aquatic organisms with high nutritional value through an eco-design concept like integrated multitrophic aquaculture (IMTA).

IMTA with Recirculating Aquaculture Systems

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Abreu et al. (2010) evaluated the potential use of macroalgae G. vermiculophylla as a biofilter component in turbot culture on land; the researchers concluded that G. vermiculophylla is an efficient component of land-based integrated multitrophic aquaculture systems, with potential environmental and economic benefits for fish farms. Meanwhile, Yokoyama and Ishihi (2010) evaluated the cultivation of Ulva ohnoi macroalgae within fish cages, indicating that this species is suitable to be used as a biofilter.

In Canada, Ridler et al. (2007) report that a pilot project cultivated macroalgae: Saccharina latissima and Alaria esculenta, with blue mussels (Mytilus edulis) and salmon (Salmo salar) in the Bay of Fundy, determining that macroalgae growth rate increased by 46% and by over 50% for mussels.

A recent study by Huo et al., (2024) evaluated the potential of integrating recirculating aquaculture systems and Integrated Multi-trophic Aquaculture; highlighting the growth results in yellowtail amberjack (Seriola dorsalis) and the macroalgae Ulva lactuca.

IMTA and Biofloc System

De Morais et al., (2023) evaluated the integrated culture of white shrimp (Penaeus vannamei) as the main species, Nile tilapia (Oreochromis niloticus) as organic consumer, and seaweed (Ulva ohnoi) as inorganic consumer in a biofloc system.

IMTA in Land-Based Ponds

Meanwhile, Omont et al., (2020) studied the co-culture of marine shrimp (Penaeus vannamei) and Pacific oyster (Crassostrea gigas) in an integrated multitrophic aquaculture system, reporting that the total sedimentable particles in the water were significantly reduced, and concluding that this type of cultivation system imposes changes in the dynamics of the digestive microbiota, which can improve water quality and shrimp productivity.

Conclusion

Integrated Multi-trophic Aquaculture is a promising alternative to traditional aquaculture. It offers a series of advantages, benefits, and solutions to the challenges facing food production. With continuous development and investment, IMTA can play an important role in meeting the world’s food needs sustainably.

In this way, Integrated Multitrophic Aquaculture systems have become a good alternative to diversify aquaculture operations, but above all to ensure their sustainability. However, there are still a series of challenges that must be overcome for them to become a commercially viable option.

Researchers and companies have the task of bringing these integrated multitrophic aquaculture experiences to a commercial scale; while lawmakers and governmental entities must create the legal framework to encourage this type of practices.

References

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