Integrated multi-trophic aquaculture (IMTA) in marine temperate waters

What is important is that the appropriate organisms are chosen based on the functionsthey have in the ecosystem, their economic value or potential, and their acceptance byconsumers. While IMTA likely occurs due to traditional or incidental, adjacent cultureof dissimilar species in some coastal areas (Troellet al., 2003), deliberately designedIMTA sites are, at present, less common. Moreover, they are presently simplifiedsystems, like fish/seaweed/shellfish. In the future, more advanced systems with severalother components for different functions, or similar functions but different size rangesof organic particles, will have to be designed (Chopin, 2006).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 (fedanimals) are converted into fertilizer, food and energy for the other crops (extractiveplants and animals), which can in turn be sold on the market. Feed is one of the coreoperational costs of finfish aquaculture operations. Through IMTA, some of thefood, nutrients and energy considered lost in finfish monoculture are recaptured andconverted into crops of commercial value, while biomitigation takes place. In this wayall the cultivation components have an economic value, as well as a key role in servicesand recycling processes of the system, the harvesting of the three types of cropsparticipating in the export of nutrients outside of the coastal ecosystem.IMTA is considered more sustainable than the common monoculture systems – thatis a system of aquaculture where only one species is cultured – in that fed monoculturestend to have an impact on their local environments due to their dependence ofsupplementation with an exogenous source of food and energy without mitigation(Chopinet al., 2001). For some twenty years now, many authors have shown that thisexogenous source of energy (e.g. fish food) can have a substantial impact on organicmatter and nutrient loading in marine coastal areas (Gowen and Bradbury, 1987; Folkeand Kautsky, 1989; Chopinet al., 1999; Cromey, Nickell and Black, 2002), affectingthe sediments beneath the culture sites and producing variations in the nutrientcomposition of the water column (Chopinet al., 2001).