The potential use of the Materials and Energy Flow Analysis (MEFA) framework to evaluate the environmental costs of agricultural production systems and possible applications to aquaculture

Global aquaculture production is roughly doubling every ten years, thus raising sustainability concerns and motivating the development of tools to evaluate its environmental costs. This paper reviews the potential contribution of material flow analysis (MFA) and the human appropriation of net primary production (HANPP) in this context. MFA and HANPP are indicators included in the broad framework of material and energy flow analysis, abbreviated MEFA framework. MFA reports physical flows in tonnes per year through various socio-economic systems, including companies, economics sectors, households, national economies, villages or world regions. MFA is increasingly used to quantify material requirements and wastes/emissions of production systems, and can be used in comparative studies, given appropriate standardization. HANPP is an indicator of land-use intensity that is often used with reference to a defined territory. HANPP is the difference between the net primary productivity (NPP) of potential natural vegetation and the proportion of the NPP of actual vegetation remaining in the ecosystem after harvest. We conclude that the combined use of MFA and HANPP could support the comparative assessment of environmental costs of aquaculture, which would require further methodological developments. INTRODUCTION Globally, aquaculture supplies increasing amounts of aquatic animals such as fish, crustaceans and molluscs. More than 220 aquatic species are farmed, and the output 1 helmut.haberl@uni-klu.ac.at Comparative assessment of the environmental costs of aquaculture and other food production sector 98 of aquaculture doubles roughly every 10 years (Naylor et al., 2000), thus supplying valuable protein for human nutrition and economic benefits. Aquaculture currently accounts for more than one third of total global food fish production, and this share is rising constantly, as capture fisheries are stagnating due to the depletion of many fish stocks (Figure 1; Pauly et al., 2002; Troell et al., 2004).2 Aquaculture production is forecast to continue to grow, with some scenarios assuming a total output of aquaculture in 2020 of over 80 Mt/yr (Delgado et al., 2003; FAO, 2004). The surging output of aquaculture systems has triggered concerns about environmental issues, such as pollution resulting from effluent discharge, loss of valuable habitats (e.g., mangrove forests), escape of farmed organisms affecting wildliving stocks (“biological pollution”), depletion of wild-living stocks due to the use of wild-caught juveniles in aquaculture systems, and environmental costs associated to feed procurement (Delgado et al., 2003; Naylor et al., 2000; Valiela , Bowen and York, 2001). Many people hope that aquaculture can compensate shortfalls in ocean fish catches caused by deterioration of fish stocks (Delgado et al., 2003; FAO, 2004). Aquaculture systems, however, often require feed containing fish meal derived from capture fisheries, so it very much depends on the origin of feed whether aquaculture can relieve pressures on wild fish populations. Fish meal derived from ocean fisheries is also used in some terrestrial animal rearing systems, above all for poultry, but some aquaculture systems currently require considerably more fish protein inputs than these terrestrial systems. Sometimes aquaculture systems, above those in which predatory species are cultivated, use about 5 times more protein from wild catch than their product contains (Naylor et al., 2000; Pauly et al., 2002). All these issues raise concerns about the sustainability of aquaculture, thus motivating efforts to develop tools to evaluate its environmental costs. This paper reviews the potential value of using methods of material and energy flow accounting (MEFA) in this context. It should be clear, in any case, that these methods cannot address all the environmental issues associated to aquaculture, i.e. they have to be seen as complementary to other methods and tools. 0 20 40 60 80 100 120 140 160 19 50 19 55 19 60 19 65 19 70 19 75 19 80 19 85 19 90 19 95 20 00 M i ll io n t o n n es 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%