Sustainability assessment concept

Sustainability can be defined as the process of people maintaining change in a homeostasis-balanced environment, in which the exploitation of resources, the direction of investments, the orientation of technological development, and institutional change are all in harmony and enhance both current and future potential to meet human needs and aspirations.

Due to integrated multi-trophic systems, some of the uneaten feed and wastes, nutrients, and by-product are recaptured and converted into harvestable and healthy seafood, which makes IMTA a driver for the sustainability of the sector. It is important to highlight the sustainability attributes associated with multi-trophic systems. 

In the IMPAQT project, the sustainability of the Multi-trophic system is addressed under a holistic perspective, where environmental, social, economic and ecosystem dimensions are included.

The two approaches considered in the assessment to analyse the environmental and eco-efficiency profile of the IMTA farms are (both based on ISO standards):

  • an LCA study, and
  • an eco-efficiency assessment. 

Both methodologies allow quantifying the benefits when moving from monoculture to IMTA systems.

Life Cycle Assessment 

Life cycle assessment (LCA) is an analysis technique to assess environmental impacts associated with all the stages of a product's life. LCA has been widely applied in the environmental assessment of products and services during the last decades, and in aquaculture to some degree in the last 20 years. For an LCA it is important to define: the goal, scope and functional unit; the assumptions; and the limitations of the study.

Most LCA studies applied to the aquaculture sector have established the functional unit based on the mass live-weight of seafood. Below is an example of system boundaries, as defined for a pilot in the IMPAQT project. Some authors have highlighted the importance of including infrastructure. These are the elements related to buoys, platforms, cages, etc 

Inputs and outputs for salmon farming in MI-Coastal site(The frame with dotted line indicates the additional species in IMTA scenario). 

Regarding multi-trophic products, some studies have applied the LCA in the evaluation of the environmental performance - two relevant examples are the IDREEM project ( and the INTEGRATE project (, which quantify the environmental benefits associated to multi-trophic under the same methodological approach than the used in IMPAQT. 

One of the more comprehensive analyses (Beltran, et al., 2017) carries out a comparative analysis for the evaluation of the environmental impacts of 1 kg of whole boxed and gutted packed finfish (sea bass and sea bream) produced in monoculture and in IMTA conditions (with oysters). They conclude marginal differences between the impacts of IMTA and monoculture fish productions, although IMTA performs better for most of the impacts studied.

Medeiros, et al., 2017 analyses the variations on the environmental profile of two Brazilian native species in monoculture (Colossoma macropomum and Macrobrachium amazonicum) and polyculture (these two species together in different spaces configurations). The conclusions reveal that the M. amazonicum had the highest impacts for all categories, while the polyculture in ponds presented better environmental performance. 

The environmental benefits associated to the multi-trophic systems are commonly related to the eutrophication reduction potential. For example, it has been estimated that 2.3–4.4 kg of dissolved nitrogen (N) could be removed per kg of kelp (Alaria esculenta and Saccharina latissima) co-cultured in the proximity of Atlantic salmon (Salmo salar) pens (Reid, et al., 2013). Whenever the bioremediation efficiency increases, the contributions towards eutrophication decrease, improving the environmental performance of the systems in this impact category (Prescott, 2017).

However, a recent study (Chary, et al., 2020) has revealed that despite the eutrophication impact being reduced, the cumulative energy demand and climate change impacts can be higher in some polyculture scenarios. Likewise, the environmental impacts of seafood products production largely depend on the technologies and practices used at the farm.

The IMPAQT LCA study has revealed that the IMTA systems are environmentally attractive as the impacts caused by the production of biomass can be reduced. The investigation suggests that the environmental profile of IMTA products in reference to the protein-provided IMTA systems perform better and marine eutrophication is reduced. There is not always an improvement, the additional infrastructure elements required to add species bring costs. While eutrophication impact is reduced due to the removal of nitrogen, there are some environments where this is not desirable. Adding additional infrastructure can affect the visual and navigational impacts. 

For the Inventory Analysis, data is collected to quantify inputs and outputs through the system boundaries. The Life Cycle Impact Assessment (LCIA) is the phase where the inputs and outputs are translated into impact indicators related to the natural environment and resource depletion. Each data point is assigned within the resource use and emissions profile to the relevant impact categories, and factors are applied to each input and output flows in order to obtain aggregated impacts within each impact category.

Environmental Assessment 

To assess how the IMTA approach would affect the environmental performance, we compared the environmental profile of the production of seabass (Dicentarchus labrax) in monoculture condition with the same production in polyculture conditions together with mussels (Mytilus galloprovincialis) and seaweed (Ulva rigida), elaborating a life cycle inventory and assessing the environmental impact associated to each input and output needed to produce 1 ton of Seabass protein. The system boundaries covered the farming operation (on growing phase), together with harvesting and packaging activities, which are done on-premises. Elements are removed from the comparison where it is assumed to be similar for monoculture and polyculture. As the system is open a black-box approach is applied to evaluate the environmental impacts (calculated based on load emissions). Nutrient retention is calculated basing on the quantity of nutrients removed when these species are harvested.

The base methodology chosen for IMPAQT study is the Environmental Footprint (EF). The baseline conditions are assessed quantifying the environmental impacts associated to the inventory flows, in a number of impact categories, to produce biomass. The impact categories are:

  • Climate change (CC) - Radiative forcing as global warming potential (GWP100)
  • Ozone depletion (OD) - Ozone depletion potential
  • Acidification terrestrial and freshwater (AC) - Accumulated exceedance (AE)
  • Ecotoxicity freshwater (ET) - Comparative toxic unit for ecosystems
  • Land use (LU) - Soil quality index
  • Resource use, energy carriers (RE) - Abiotic resource depletion – fossil fuels (ADP-fossil)
  • Resource use, mineral and metals (RM) - Abiotic resource depletion (ADP ultimate reserves)
  • Water footprint (WF) - Relative available water remaining per area
  • Freshwater eutrophication (EF) - Expression of the degree to which the emitted nutrients reach the freshwater end compartment (phosphorus considered as limiting factor in freshwater).
  • Marine eutrophication (EM) - Expression of the degree to which the emitted nutrients reach the marine end compartment (nitrogen considered as a limiting factor in marine water).

The monoculture situation is compared with the IMTA situation.

With biomass as the basis of comparison, IMTA performs better in all impact categories. Particularly, impacts from feed manufacturing are diluted when the total biomass produced is assessed. That explains why impacts categories dominated by feed are notably reduced in this comparison (for example eutrophication of freshwater).

Life Cycle Assessment - Eco efficiency

Here we assess the Eco-efficiency on the IMTA site under two differentiated perspectives. 

1. Analysis of the efficiency in terms of environmental impact, and more specifically regarding the effects on marine eutrophication. The environmental profile is addressed in relation to the total proteins delivered. 

The site is able to increase its eco-efficiency when IMTA is implemented. Specifically, providing more seafood protein to markets while reducing the pressure on the marine ecosystems.

2.       The spatial use and the efficiency of IMTA systems in relation to the protein delivered per surface occupied - a sort of eco-intensification analysis that complements the conventional eco-efficiency approach.

IMTA enables an increase in biomass production, by utilising the available space more efficiently, by farming on multiple levels. This increase in biomass production within the area currently used for monoculture provides greater biomass while reducing the environmental impacts.


Beltran, A. M. et al., 2017. Accounting for inventory data and methodological choice uncertainly in a comparative life cycle assessment: the case of integrated multi-trophic aquaculture in an offshore Mediterranean enterprise. Int J Life Cycle Assess. 

Chary, K. et al., 2020. Integrated multi-trophic aquaculture of red drum (Sciaenops ocellatus) and sea cucumber (Holothuria scabra): assessing bioremediation and life-cycle impacts.  Aquaculture, Volume 516.  

Medeiros, M. V., Aubin, J. & Camargo, A. F., 2017. Life cycle assessment of fish and prawn production: Comparison of monoculture and polyculture freshwater systems in Brazil. Journal of Cleaner Production, Issue 528-537. 

Prescott, S. G., 2017.  Exploring the Sustainability of Open-water marine, Integrated Multi-Trophic Aquaculture, Using Life-Cycle Assessment, s.l.: s.n.  

Reid, G. et al., 2013. Weight ratios of the kelps, Alaria esculenta and Saccharina latissima, required to sequester dissolved inorganic nutrients and supply oxygen for Atlantic salmon, Salmo Salar, in Integrated Multi-Trophic Aquacuture Systems.  Aquaculture, pp. 34-46.  

Last modified: Thursday, 13 May 2021, 00:11