One such method is Integrated Multi-Trophic Aquaculture (IMTA), which can help address many of the environmental impacts of aquaculture. IMTA combines the cultivation of several species from various trophic levels and serving complementary ecosystem functions. Several components of IMTA systems have been identified that can be used in different combinations:
- fed aquaculture (g. finfish),
- dissolved inorganic nutrient suspension extractive aquaculture (g. seaweeds and aquatic plants),
- small organic particle suspension extractive aquaculture (g. shellfish),
- large organic particle deposit extractive aquaculture (g. other invertebrates and herbivorous fish), and
- microbial mineralising component (g. bacteria).
The aim is to ecologically engineer systems, developed on a balanced ecosystem-based management approach to aquaculture, for increased environmental sustainability (nutrient biomitigation and other ecosystem services, and green technologies for improved ecosystem health), economic stability (improved output, lower costs, product diversification, risk reduction, and job creation in coastal and rural communities), and societal acceptability (better management practices, improved regulatory governance, nutrient trading credit incentives, and appreciation of differentiated and safe products).
Diversification is essential
Monoculture in agriculture is risky, much like investing in only one stock on the stock exchange. The same is true for aquaculture: putting all your eggs in the same basket is also risky. The future growth of the aquaculture sector hinges on diversification.
Global numbers appear to show some signs of progress. For example, extractive aquaculture of seaweeds/aquatic plants/molluscs/crustaceans/non-fed finfish now represents 54.4 % of mariculture production, the remaining 45.6 % being fed species. However, this extractive/fed aquaculture split is unevenly distributed worldwide. For example, 97.6 % of seaweed aquaculture is concentrated in six Asian countries (China, Indonesia, the Philippines, the Republic of Korea, Japan and Malaysia). Consequently, if aquaculture is to make a major contribution, geographical diversification is also needed, particularly in the western world.
IMTA could provide this diversification and broaden the western, predominantly finfish aquaculture industry away from a monoculture model, improving business cases, increasing resilience and improving the societal acceptability of this industry.
Revisiting the management of aquaculture within an integrated coastal area management (ICAM) approach
It would be a complete illusion to think that an aquaculture farm functions only within the limits of a few buoys, arbitrarily placed in the water by humans. Its management should be based on an Integrated Coastal Area Management (ICAM) strategy, considering different spatial and temporal recapturing strategies to recover the different types of nutrients:
- large particulate organic nutrients should be managed within the farm,
- small particulate organic nutrients should be managed within the farm or around its immediate vicinity,
- dissolved inorganic nutrients should be managed at the ICAM scale either when produced directly or after re-mineralization of the organic matter.
This means that entire bays/coastal areas/regions should be the units of IMTA management, not relatively small finfish sites. IMTA was never conceived with the idea of being viewed only as the cultivation of salmon, kelps, blue mussels and other invertebrates, in temperate waters, and only within the limits of existing finfish aquaculture sites. This would be a very reductionist view of IMTA. That’s how we started in Canada, in order to be able to conduct experiments at sea, within the limitations of the regulations presently in place, rather than extrapolating from small tank experiments in laboratory conditions, which is always dangerous. It is time to open the Pandora’s box of regulations and develop new ones based on the recognition of the ecosystem scales at which aquaculture sites operate.
IMTA systems should and will continue to evolve. Because the IMTA concept is extremely flexible and can be applied worldwide to open-water and land-based systems, marine and freshwater environments, and temperate and tropical climates, there is no ultimate IMTA system to feed the world. Different climatic, environmental, biological, physical, chemical, economic, historical, societal, political and governance conditions will lead to different choices in the design of the best suited IMTA systems.
It is not enough to consider multiple species (like in polyculture); they have to be at multiple trophic levels, based on their complementary functions in the ecosystem. They should also have an economic value. Integration should be understood as cultivation in proximity, not considering absolute distances but, instead, connectivity in terms of ecosystem functionalities at the ICAM scale. There is nothing that says that only one company should be in charge, producing all the IMTA components. There may need to be several companies coordinating their activities within the ICAM.
IMTA is not only a catabolic cascade, but is circular in nature
Because of societal obsession with observable organic “waste” accumulation at aquaculture sites, and associated regulations, we risk not understanding the implicit need for IMTA to be circular. To date, we have mostly focused on the catabolic aspects of IMTA: the set of ecosystemic and metabolic pathways that break complex organic molecules down into simpler inorganic molecules, usually while releasing energy. However, a cascade continues to operate only if the natural cycle of water continues, or, in the case of an artificial cascade, if hydraulic systems have been engineered to send the water back up. If we want IMTA to continue to operate (be sustainable), some serious bio-engineering will also be necessary. If we, one day, succeed in developing very efficient catabolic IMTA systems, we could end up with a large amount of inorganic molecules, visually not easy to document, but potentially exceeding their levels of being beneficial nutrients and, then, being used by nuisance opportunistic species (macro- and microscopic harmful algal blooms).
Out of sight should not be out of mind. It is, consequently, very important to work on, understand, and use efficiently the anabolic aspects of IMTA: the set of ecosystemic and metabolic pathways that construct complex organic molecules from simpler inorganic molecules, usually while consuming energy. The organisms capable of this conversion are cultivated commercially opportune, or naturally occurring, autotrophs, such as macro- and micro-algae and aquatic plants, which can form the crucial inorganic extractive component of IMTA. It is important to put IMTA in its context of bio-inspired design, biomimicry, law of conservation of mass, circular economy and ICAM, to understand its full long-term relevance and design appropriate regulations.
Valuing extractive species for more than their food trading values
To bestow full value to seaweeds and other extractive species in IMTA systems, they need to be valued for not only their biomass and food trading values, but also for the ecosystem services they provide within a circular economy framework (e.g. nutrient biomitigation, irrigation-less and deforestation-less food production, oxygen provision, habitat restoration, carbon sequestration, coastal acidification reduction, etc.). The value of these ecosystem services should be recognized, accounted for and used as financial and regulatory incentive tools (e.g. nutrient trading credits).
We need to change our attitudes and business models to evolve from the linear approach (one species – one process – one product), used far too often with fishery and aquaculture products, towards the Integrated Sequential Biorefinery (ISBR) approach (one species – several processes – several products). This fits very well with the circular economy approach, in which by-products are no longer considered wastes but co-products, which can be valued in other applications. For example, seaweeds, mostly cultivated and used in Asia for human consumption, can be used in many applications. They can be used in the production, on one hand, of a wide range of bio-based, high-valued products (food and feed products/ ingredients/supplements, biopolymers, fine and bulk chemicals, agrichemicals, biostimulants, pharmaceuticals, cosmeceuticals, nutraceuticals, functional foods, biooils, botanicals, pigments) and, on the other hand, of lower-valued commodity energy carrying molecules for heat and power (biofuels, biodiesels, biogases, bioalcohols) and biomaterials.
Seaweeds can also have an impact on climate change by sequestering carbon dioxide and decreasing coastal acidification. Shellfish hatcheries are noticing increased mortality in larvae, which cannot properly calcify their shells. It would be interesting to combine seaweed and shellfish aquaculture operations where seawater would first go through seaweed tanks, to reduce acidity, before being piped into the mussel tanks where it would help larvae calcify properly. The IMTA multi-crop diversification approach (fish, seaweeds and invertebrates) could be an economic risk mitigation and management option to address pending climate change and coastal acidification impacts. IMTA systems could be associated with offshore wind farms. These are often exclusion zones where no other activities are permitted. Using the pillars of wind turbines as infrastructures for IMTA systems would allow for the combination of these two activities, and, consequently, reduce their footprint through sharing, which should increase their respective societal acceptability.
IMTA could also be a model of benign aquaculture practices compatible with activities in Marine Protected Areas (MPAs). IMTA can provide jobs in sustainable development related activities (local eco-tourism, seafood production, restaurants, etc.) for local communities, which are, then, not displaced, as has been the case with the development of reserves for well-off tourists. IMTA can also provide local food and nutrition security, alleviate poverty, and contribute to the socio-economic resilience of local communities. Eco-tourism could significantly help the aquaculture sector gain societal trust and licence to operate. As IMTA development is presently hindered in several countries (including Canada) by obsolete policies and regulations, and MPAs are not always easy to establish, teaming-up would help validate their convergent approach through a number of concrete case studies.
The need for enabling regulations instead of maintaining regulatory hurdles
For IMTA to be developed, implemented and scaled up in Canada (and other jurisdictions) some seriously impeding regulations need to be addressed and changed into enabling and flexible regulations, so that they do not continue to be unnecessary, hampering, regulatory hurdles. Regulations governing aquaculture are often designed with a single species/group of species in mind, just like fishery regulations, and can inhibit a more holistic approach by not considering species interactions and an ecosystem-based management approach.
To move toward an ICAM approach, effective and coordinated regulations that enable new practices, new industries, and establish new markets are needed. The changes will vary from country to country, but this has been a recurrent source of frustrations for all people promoting IMTA in their respective countries. It is, however, important to engage regulators early on, as trends start to appear, so that regulations are well thought-out, instead of rushed at the last minute, which inevitably leads to delays in commercialisation.
Rethinking for whom the IMTA concept is the most appropriate in the western world
Based on experience acquired over the last 17 years, it appears that very small players in the industry struggle to implement the necessary systems, while large players, who need IMTA the most, prefer to focus on their core business, typically salmon. Like in many sectors, small and medium-sized enterprises (SMEs) seem to be the most interested – they are flexible and innovative, and want to differentiate themselves, particularly as their industries are affected by consolidation. The combinations of co-cultured species will have to be carefully selected according to a variety of conditions and criteria. Within an effective IMTA system, peak production may not be achieved for any one species. Rather, the focus would be on optimising sustainable production and the overall performance of all the combined species in the long term.
Moving IMTA along the research, development, and commercialisation (R&D&C) continuum, in the western world, will require profound regulatory changes. It will also require the demonstration of the validity of the concept at multiple levels. If evidence of increased environmental sustainability and societal acceptability have been provided in recent years, the economic stability demonstration remains to be further established, especially over the long term. It will be important to explore opportunities for diversification, the source of further development in the aquaculture sector.
It is time to develop aquanomic principles, as agronomic principles emerged over the last centuries. It is time to morph the Blue Revolution and Blue Economy into a greener and transformative Turquoise Revolution and Turquoise Economy. It is also important to remain patient, determined and persistent. Science and society need time to think and evolve. IMTA will not happen overnight, especially in the western world, which presently prefers monocultures, linear processes, and short-term profits.