Aquaculture plays a crucial role in food security and provision of income and livelihoods for communities. Following recognition as the most promising source of animal protein and essential nutrients worldwide , there has been significant investment and growth in this sector. However, this increasing contribution to global aquatic food supply is hindered by sustainability challenges . Integrated multi-tr ophic a quaculture (IMTA) represents a sustainable production method combining the farming of multiple, complementary species from different trophic levels , and could reduce environmental impacts, diversify, and increase aquaculture production. As part of the All-Atlantic Ocean Sustainable, Profitable and Resilient Aquaculture (ASTRAL) project, we have investigated the benefits for the integrated cultivation of abalone (Haliotis midae) and sea urchin (Tripneustes gratilla ) with the green seaweed Ulva lacinulata in land-based, partially recirculated aquaculture systems in South Africa.
Production of abalone or urchin in systems integrated with seaweed has shown numerous benefits. IMTA grown Ulva is an excellent source of minerals, vitamins, AA’s, FA’ s, protein, complex polysaccharides, and other bioactive compounds. When used as a feed or a feed component , we have shown that Ulva enhances the chemosensory properties of formulated feeds, and significantly improves feed conversion ratio (FCR), feed consumption and digestible protein intake. Existing pigments in the seaweed (e.g., β-carotene ) enhance the colou r and marketable properties of urchin gonads. Ulva also has additional benefits in that it reduces nutrient release from farms into the sea ( from 0.6 3-0.38t of N per urchin production cycle) , reduces reliance on harvesting natural seaweeds and reduces dependence on the use of protein-rich formulated feeds ( ca. 20% cost saving) . The bioremediation ability of Ulva reduced energy consumption from 10.35-6.80 kWh per ton abalone biomass and 12.45- 3.54 kWh per ton urchin bio mass harvested when recirculation rates are increased from 0-50% and 0-90% for the abalone and urchin IMTAs, respectively . A perceived risk of growing Ulva in abalone effluent and utilizing it as a supplementary feed is biosecurity — which has hampered broader uptake of IMTA. However, our comprehensive m icrobiome studies have revealed high microbial diversity in all compartments of the IMTA, indicative of a healthy system, and Ulva exhibits a modulatory effect on the microbiome , reducing abundance of opportunistic pathogens (e.g., Vibrio spp.).
Collectively, our studies revealed several benefits associated with the cultivation of Ulva in IMTA systems and high potential for IMTA to support sustainable aquaculture a nd a circular bioeconomy.
This study received funding from the EU Horizon 2020 Research & Innovation Programme ASTRAL Project under Grant Agreement No. 863034