A major hurdle facing Tasmania’s growing seaweed aquaculture industry is low nutrient levels in our waters which can limit the growth of cultivated seaweeds. Salmon aquaculture faces the opposite challenge where excess nutrients produced by farming can have negative environmental effects. Integrated Multi-Trophic Aquaculture (IMTA) is the idea that nutrients released into the environment by species like salmon can be used by species that need to uptake nutrients from the water, such as seaweeds, by growing them in proximity to each other (known as co-culturing). The result can be positive for the environment and production.
This Honours research project investigated the feasibility of co-culturing salmon and seaweed in Tasmania by first seeking to understand whether cold-water seaweeds can effectively use nutrients released into the environment by salmon farming. Using a stable isotope analysis method, the project investigated how a range of seaweed species with different growth and reproductive strategies uptake nutrients in both laboratory and real-world situations.
Field experiments involved identifying the isotopic composition of seaweeds (Ecklonia radiata, Asparagopsis armata and Ulva spp.) deployed across a range of distances from an active salmon lease in Tasmania across both stocking and fallowing cycles. Laboratory experiments involved analysing the isotopic composition of seaweed (Ulva spp.) dosed with varying concentrations of salmon effluent water.
It was found that seaweeds were using nitrogen released by the salmon farm for growth, with the isotopic composition of the seaweeds allowing the spatial nitrogen footprint of the farm to be determined. Insights were also gained into the physiological differences in the nitrogen uptake and storage capacities across the three algae species. The laboratory experiment demonstrated that isotopic composition of Ulva spp. was significantly influenced by salmon effluent in a controlled environment. Ultimately, both the field and lab experiments supported the hypothesis that the isotopic composition of seaweeds would reflect nitrogen released by salmon aquaculture.
Honours student: Riana Bell
