48 SEPTEMBER 2024 • WORLD AQUACULTURE • WWW.WAS.ORG effectively than chemoautotrophic bacteria and use the available ammonia to grow bacterial biomass (Brandão et al. 2021). Control of nitrogenous compounds occurs more rapidly, with greater production of total suspended solids in the system, which may require the use of clarification to maintain optimal levels. The use of an inoculum from an ongoing cultivation system with established heterotrophic and chemoautotrophic bacteria also offers greater control of nitrogen compounds and water reuse (Krummenauer et al. 2014). Targeting one of these systems influenced the macroalgae’s performance, showing that in the chemoautotrophic system, the low production of solids provided a constant growth rate over the course of cultivation (Figures 2 and 3). For the heterotrophic system, despite the biomass gain, the accumulation of solids of approximately 400 mg L-¹ compared to 200 mg L-¹ in the chemoautotrophic system caused a decrease in the macroalgae’s growth rate in the last few weeks of cultivation, due to the presence of biofloc on the algae tissue and low light levels. This biomass production in both treatments is associated with the absorption of nutrients by the macroalgae, with an overall average nitrate removal rate of 56.7%. However, the phosphate removal rate in the heterotrophic treatment was higher at 56% compared to the chemoautotrophic treatment at 47%. This is due to the better nitrogen: phosphorus balance found in the system and the maintenance of lower pH values, which help to remove phosphorus compared to the chemoautotrophic system (Rathod et al. 2014, Zirino et al. 2016)measured as total dissolved N (TDN. Additionally, the higher nutrient absorption rates in the heterotrophic system led to differences in the protein content of the macroalgae tissue, with a value of 18.5% compared to 15.3% in the chemoautotrophic treatment, providing an advantageous characteristic for the marketing of the macroalgae. Despite the higher level of protein, the lower organic load in the chemoautotrophic system resulted in better growth rates in the macroalgae, making it a viable system for production. FIGURE 2, top and bottom. Macroalgae specific growth rate (% day -1) in the chemoautotrophic (chemical fertilization prior to stocking) and heterotrophic (use of an inoculum from an ongoing biofloc shrimp cultivation) treatments in an integrated cultivation of Ulva lactuca with Oreochromis niloticus and Penaeus vannamei. An asterisk (*) means a statistical difference on the same day between treatments. Letters mean differences in the same treatment between sampling days. A B FIGURE 3. Low production of solids in the chemoautotrophic system provided a constant growth rate over the course of cultivation.
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