46 SEPTEMBER 2024 • WORLD AQUACULTURE • WWW.WAS.ORG Different Depths of Cultivation Structures Due to the distinct characteristics of the biofloc system, such as high turbidity, solids, and nutrients, it is necessary to adopt management practices that maximize the production of macroalgae in an integrated system. The use of cultivation structures for macroalgae in a closed biofloc system is required due to the intense aeration responsible for suspending the microbial flocs and to avoid possible herbivory from the organisms cultivated with the macroalgae. Different cultivation depths can affect various aspects of macroalgae development. Due to the number of particles suspended in the biofloc, light intensity decreases with increasing depth (Reis et al. 2019). Therefore, shallow depths keep the macroalgae closer to the surface, allowing them to absorb more light. However, shallow structures have less support capacity for the constant growth of the macroalgae, which can negatively affect their performance (Alencar et al. 2010). To this end, two cultivation depths were tested: shallow (0.1 m from the surface) and deep (0.3 m from the surface) in an integrated system with shrimp, Litopenaeus vannamei, and tilapia, Oreochromis niloticus, on a pilot scale. The results showed that, despite the greater space for macroalgae movement within the ‘deep’ structure, the growth rate in the ‘shallow’ structure was significantly higher throughout the experiment (Figure 1). However, the density in the shallow cultivation structure became a problem towards the end of cultivation, as the increase in biomass over time led to overlapping of the macroalgae and shading, which resulted in a decrease in biomass in the final weeks of cultivation. Therefore, the use of 0.1 m deep cultivation structures maximizes the production of macroalgae biomass in an integrated biofloc system. Another factor tested was the influence of the macroalgae on the concentration of total suspended solids in the system. For this purpose, the concentration of suspended solids in the water was measured with the macroalgae in the tank and after the macroalgae had been removed. It was observed that the deposition of solids on the surface of the macroalgae occurred in both cultivation structures, causing a lower concentration of suspended solids in the tank (Table 1). As a sessile organism, under these cultivation conditions, the macroalgae functioned as a physical barrier to the movement of water, causing the solids to be trapped on the surface of their lamellae. When the macroalgae was removed from the tank and the organic matter was suspended again, there was an average increase of 40% in the solids in the tank (Table 1). Large quantities of solids can be damaging to the shrimp by occluding the gills (Gaona et al. 2017), as well as to the macroalgae by reducing photosynthesis. It is therefore necessary to evaluate solids levels to improve the algae’s performance in the system. Effect of Different Concentrations of Solids and Nutrients The use of a biofloc inoculum from an ongoing system represents a sustainable alternative with better control of nitrogen compounds (Brandão et al. 2021). Consequently, the accumulation TABLE 1. Concentrations of suspended solids (TSS) (mean ± standard deviation) of the treatments shallow float (5 to 10 cm depth) and bottom float (25 to 30 cm depth), with and without macroalgae in the tank, during 70 days of experiment. TREATMENTS SHALLOW FLOAT BOTTOM FLOAT Parameters with Macroalgae without Macroalgae with Macroalgae without Macroalgae TSS (mg L-11) 305.10 ± 84.10 a 503.80 ± 40.10 b 317.00 ± 71.30 a 530.30 ± 40.10 b Different letters represent significant differences (p ≤ 0.05) with and without macroalgae in the same treatment after Student’s t-test (n = 12). FIGURE 1, left and right. Mean macroalgae weight (kg—fresh weight) of the treatments, shallow float (between 5 to 10 cm depth) and bottom float (between 25 to 30 cm depth) during the 70 days of experiment. Asterisks (*) represent significant differences (p ≤ 0.05) among treatments after Student’s t-test (n = 3). A B
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