Waste removal efficiencies of IMTA

Offshore aquaculture production is expected to expand as a result of increasing demands for food and energy, and the scarcity in terrestrial space. Along with this, arises the concern of negative impacts on the environment as a result of increasing aquaculture waste discharges. A suggested solution is to combine the cultivation of fed species, like finfish, with extractive species like seaweeds and bivalves which are able to remove nutrients from the water column, and deposit feeders which are able to take up nutrients settling at the sea bottom. In this way, waste produced by one species, becomes a resource for other species of a lower trophic level. This concept is referred to as Integrated Multi-Trophic Aquaculture (IMTA), and aims to create production systems which are simultaneously ecological sustainable and produce additional valuable products. Although the general concept and principles of the IMTA approach are straightforward, difficulties exist in quantifying the efficiency of IMTA systems, in terms of their potential to remove waste nutrients. This is especially the case for integrated systems in open water, where environmental factors are difficult to control. It is therefore important to get a better understanding of waste retention efficiencies of various extractive species under different scenarios.