Evaluating Native Macroalgae Species of the Southeast U.S. and Caribbean Region for Use in Integrated Multi-Trophic Aquaculture (IMTA)

Global human population is predicted to approach 10 billion by 2050, prompting an increased need to produce protein to support human dietary demands (FAO, 2022). Aquaculture food production will help address this increased demand for protein production. Integrated multi-trophic aquaculture (IMTA) represents a potentially more sustainable approach to aquaculture than traditional monoculture of a species within a single trophic level. This study analyzed a pilot-scale IMTA system composed of a culture tank of yellowtail snapper (Ocyurus chrysurus) cultured at a commercial-scale density, while using the nutrient rich effluent water from the culture tank to supply replicated macroalgae raceways containing four different species of macroalgae (Agardhiella subulata, Caulerpa racemosa, Gracilaria caudata, and Ulva lactuca) that are native to the Southeast U.S. and Caribbean regions. Water temperature, dissolved oxygen (DO), salinity, alkalinity, pH, phosphorus, total ammonia nitrogen (TAN), and CO₂ data readings were taken daily over the course of the research trials. Seaweed samples of each species were analyzed for protein, fat, fiber, ash, minerals, and metals. Additionally, the carbon and nitrogen isotopes of the seaweed species were elementally analyzed. Results indicate that Agardhiella subulata reduced the tank ammonia concentrations the most throughout the trial, and Ulva lactuca with its exponential increase in uptake reached below detectable limits of TAN by day 9 of the trial. The compositional analysis indicated Caulerpa racemosa had the highest protein content and Ulva lactuca had the highest carbohydrate content. The calculated CO₂ concentration and the carbon:nitrogen ratio data indicated that Ulva lactuca up took and incorporated carbon most efficiently. The results of this project provide novel information for existing and prospective IMTA operations throughout the Southeast U.S., Gulf, and Caribbean regions and allows producers to make well-informed decisions on candidate culture species of macroalgae for IMTA systems.