Efficiency and environmental performance of IMTA in marine and freshwater systems

Introduction For some years now, IMTA (Integrated MultiTrophic Aquaculture) concept has gained worldwide attention. Integrating complementary species such as fed aquaculture species (e.g. finfish), inorganic extractive aquaculture species (e.g. phytoplankton and seaweeds) and organic extractive species (e.g. bivalves, sea-urchins, and sea-cucumbers) is an attractive concept to enhance the efficiency of aquaculture (Neori et al., 2004). IMTA has the potential to increase profitability while simultaneously act as bioremediator of effluents. The environmental and economic costs of feed are high and the expected increase of aquaculture in the future, demands a more efficient use of nutrients highlighting the potential role of recycling mass and energy in the systems (Naylor et al., 2000). Some advantages of the use of IMTA are (1) decrease the dependence on external inputs, (2) increase the system efficiency by optimizing the use of nutrients and energy in the production loop, (3) decrease the waste effluents and bio-deposit impacts by limiting the loss of nutrients (in water, sediments and air), (4) diversify farm- products and generate a more robust source of income (less dependent on mono-product markets), and (5) generate and use different types and levels of ecosystem functions and services. Despite the potential benefits of IMTA its development is still limited in Europe. Many factors can explain this situation and among them, the performance of the extractive organisms and the economic performance of the systems (Hughes and Black, 2016). The lack of knowledge, expertise and reference data for dimensioning and optimizing the systems, and their intrinsic complexity are still prevalent. There is need for greater body of evidence of the financial benefit to the farmer, better ways to reduce the system complexity, and better support from policy and regulation to reinforce the increase in social license associated with IMTA. The proof of concept has to be established and confirmed in different systems' configuration. Material and methods IMTA-EFFECT (Integrated MultiTrophic Aquaculture for EFFiciency and Environmental ConservaTion) is an EU ERA-NET project aiming to evaluate the performance of several European systems (and also few tropical systems) in order to provide references data for implementing IMTA. Several IMTA approaches were integrated for this purpose. Experiments are conducted in different countries and contexts: multitrophic marine systems (in Portugal, France and Greece) combining fish, algae, filter and/or deposit feeders; and fresh water polyculture systems (in Romania, France, Indonesia and Madagascar) combining fish and plants (micro and macrophytes). These systems were conceived according to two modalities: 1- species reared separately in different structures allowing a precise measurement of each species activities and their role in nutrient and energy cycling, 2- species reared all together in the same structure, showing an overall performance of species interactions. Modelling is the common methods to evaluate the fate of nutrient and energy in the system and among the different species. Mass balance has been established in each system. ECOPATH (Christensen and Pauly , 1992; Pauly et al ., 2000) is being used in the systems where species are reared all together to assess the interactions of trophic levels, including the produced species (Gamito and Erzini, 2005; Xu et al., 2011). Dynamic Energy Budget modelling is used mostly in the systems where species are reared separately to investigate how different types of food (quality and quantity) will affect growth performances and nutrient excretion of cultivated species (Pouvreau et al., 2006). Both methods are being calibrated and validated using carbon and nitrogen stable isotopes and fatty acid analyses, which help to characterize the different pathways of energy and nutrients between the species and compartments, and therefore the efficiency of the studied IMTA systems. In a more advanced stage of the project, Emergy accounting (Odum, 1996) and Life Cycle Assessment (Wilfart et al., 2013) will permit to characterize economic and environmental performances at a more global level. Finally, the perception of stakeholders including aquaculture farmers and policy makers, for ecosystem services provided by IMTA will be studied to draw specific future prospects of development. Results IMTA Effect project is still in progress. The implementation of the several IMTA approaches will contribute to better integrate and root the production system in the territory, particularly in the ecosystem, and the socioeconomic environment. Main features of different systems under study and preliminary results will be presented. (Resume d'auteur)