Innovative Practices Need to be Developed

The challenge, then, is how to increase the production capacity of an existing site (increased production per area without exceeding the ecosystem assimilative capacity) when the other options have shown their limitations. One of the possible answers is to increase the level of technol ogy involved in the production of seafood so that food and waste handling systems are all actively considered in the system design and operation protocols from the start, and are modeled after natural ecosystems (or, at least, that resource utilization is maximized by adding functionally different species to the cultivation system).

One of the innovative solutions being proposed for environmental sustainability, economic diversifica tion, and social acceptability, is integrated multitrophic aquaculture (IMTA). This practice combines, in the appropriate proportions, the cultivation of fed aquaculture species (e.g., finfish) with organic extractive aquaculture species (e.g., shellfish) and inorganic extrac tive aquaculture species (e.g., seaweed) for a balanced ecosystem management approach that takes into consid eration site specificity, operational limits, and food safety guidelines and regulations (Figure 1). The aim is to increase long term sustainability and profitability per cultivation unit (not per species in isolation as is done in monoculture), as the wastes of one crop (fed animals) are converted into fertilizer, food, and energy for the other crops (extractive plants and animals), which can in turn be sold in the market. Feed is one of the core operational costs of finfish aquaculture operations. Through IMTA, some of the food, nutrients, and energy considered lost in finfish monoculture are recaptured and converted into crops of commercial value, while biomitigation takes place. In this way all the cultivation components have an economic value, as well as a key role in services and recycling processes of the system, the harvesting of the three types of crops participating in the export of nutri ents outside of the coastal ecosystem (Figure 2). It is important to consider that these systems do not work in isolation and that solar energy and atmospheric and ter restrial inputs must also be factored in. Moreover, the

Figure 1 Conceptual diagram of an integrated multitrophic aquaculture (IMTA) operation including the combination of fed aquaculture (e.g,. finfish) with organic extractive aquaculture (e.g., shellfish), taking advantage of the enrichment in particulate organic matter (POM), and inorganic extractive aquaculture (e.g., seaweeds), taking advantage of the enrichment in dissolved inorganic nutrients (DIN).

biomass and functions of the fed and extractive species naturally present in the ecosystem in which aquaculture farms are operating must also be accounted for or this will lead to the development of erroneous carrying capacity models.

The IMTA concept is extremely flexible. It can be applied to open water and land based systems, and mar ine and freshwater systems (sometimes then called 'aquaponics' or 'partitioned aquaculture'). What is impor tant is that the appropriate organisms are chosen based on the functions they have in the ecosystem and, moreover for their economic value or potential. What is quite remarkable, in fact, is that IMTA is doing nothing other than recreating a simplified, cultivated ecosystem in bal ance with its surroundings instead of introducing a biomass of a certain type one thinks can be cultivated in isolation of everything else. By using extractive species for the biomitigation of fed species activities, the envir onmental costs of a fed monoculture are internalized, hence increasing the overall profitability of the IMTA farm, especially when the costs and benefits to nature and society of aquaculture wastes and their mitigation will be quantified and associated with discharge regulations.

The paradox is that IMTA is not a new concept. Asian countries, which provide more than two thirds of the world's aquaculture production, have been practicing IMTA, through trial and error and experimentation, for centuries. Even if the cultured species are different (Figure 3), why, then, is this common sense solution not more widely implemented, especially in the western world? The reasons for this generally center around social customs and practices that we are already familiar with,

Ecosystem-based integrated multitrophic aquaculture management concept

Atmospheric inputs

Atmospheric inputs

Energy Flow Imta

Figure 2 Ecosystem-based integrated multitrophic aquaculture (IMTA) management concept. The wastes of one crop (fed animals) are recaptured and converted into fertilizer, food, and energy for the other two crops of commercial value (extractive plants and animals), while biomitigation takes place and the harvesting of the three types of crops participates in the export of nutrients outside of the coastal ecosystem. Solar energy and atmospheric and terrestrial inputs must also be factored in. The biomass and functions of the fed and extractive species naturally present in the ecosystem in which aquaculture farms are operating must also be accounted for.

Figure 2 Ecosystem-based integrated multitrophic aquaculture (IMTA) management concept. The wastes of one crop (fed animals) are recaptured and converted into fertilizer, food, and energy for the other two crops of commercial value (extractive plants and animals), while biomitigation takes place and the harvesting of the three types of crops participates in the export of nutrients outside of the coastal ecosystem. Solar energy and atmospheric and terrestrial inputs must also be factored in. The biomass and functions of the fed and extractive species naturally present in the ecosystem in which aquaculture farms are operating must also be accounted for.

100 80

100 80

Fish

Mollusks

Crustaceans

Marine plants

World

Asian countries

Western countries

Figure 3 World aquaculture biomass production of the four major farmed groups (fish, mollusks, crustaceans, and marine plants) and differences in their distribution (%) between Asian and Western world countries.

Fish

Mollusks

Crustaceans

Marine plants

World

Asian countries

Western countries

Figure 3 World aquaculture biomass production of the four major farmed groups (fish, mollusks, crustaceans, and marine plants) and differences in their distribution (%) between Asian and Western world countries.

even if common sense tells us that we should modify them. Human society does not change quickly unless there are compelling reasons to. The conservative nature of our marine food production industries is a good exam ple of the relative slowness with which changes are adopted, especially when dealing with a complex aquatic environment, which we mostly see only the surface of, and have difficulty understanding the processes taking place beneath it over considerable distances and volumes.

Western countries are regularly reinventing the wheel. Research on integrated methods for treating wastes from modern mariculture systems was initiated in the 1970s.

After that period, the scientific interest in IMTA stagnated, and it was not until the late 1980s and early 1990s that a renewed interest emerged, based on the common sense approach that the solution to nutrification is not dilution but conversion within an ecosystem based management perspective. In recognition of this growing interest, the Aquaculture Europe 2003 Conference in Trondheim, Norway, whose theme was 'Beyond Monoculture', was the first large international meeting (389 participants from 41 countries) with IMTA as the main topic. In 2006, at the joint European Aquaculture Society and World Aquaculture Society Conference in Florence, Italy, IMTA was recognized as a serious research priority and option to consider for the future development of aquaculture prac tices. The determination to develop IMTA systems will, however, only come about if there are some visionary changes in political, social, and economic reasoning. This will be accomplished by seeking sustainability, long term profitability, and responsible management of coastal waters. It will also necessitate a change in the attitude of consumers toward eating products cultured in the marine environment in the same way that they accept eating products from recycling and organic production systems on land, for which they are willing to pay a higher price. At the present time, several organizations are trying to modify seafood consumption tendencies by incorporating such concepts as food safety, and environmental and social sustainability.

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