The concept of Integrated Multi-Trophic Aquaculture is to allow particulate and dissolved organic wastes to be used as food source for organisms at different trophic levels. So potentially offering ecosystem services, such as bio-mitigation of waste, while diversifying production, and providing an extra source of income. Previous studies have primarily focussed on capacity of organisms to directly consume wastes of others but tend to overlook technical bottlenecks and economic investment, which might arise under a commercial IMTA set-up in coastal environments. One example is the use of sea cucumbers, which are considered a strong IMTA candidate species due to their high bio-mitigation capacity and high market value.
In this study, an organic particulate depositional model was used to assess deposition of waste feed and faeces in a hypothetical system (Figure 1) based on six commercial salmon farms in Scotland. An optimal benthic zone for sea cucumber production (the Integrated Area, IA) which excluded sediments, with depleted oxygen levels and limited particulate food supply, was developed as a spatial management tool for the deployment of sea cucumbers. Furthermore, two sea cucumber production scenarios of 500 and 200 crates (each 1 m2) were used to relate levels of stocking density to amount of waste mitigation potential based on the total area and total deposition. Finally, economic investment required for the set-up was assessed to investigate the financial cost of waste removal as an ecosystem service. Results from the models and economic analysis showed that the ecosystem services provided from this type of IMTA system for waste mitigation are very limited for full scale salmon farms in Scotland.