## 1 Introduction  
Macroalgae production in an integrated system has shown significant results, such as increased yields and nutrient removal from cultivation [1, 2, 3]. This association of organisms from different trophic levels is defined as Integrated Multitrophic Aquaculture (IMTA), which involves choosing organisms that will take advantage of organic and/or inorganic compounds in the system with the aim of reusing waste produced by the species with the highest trophic level [4]. As a result, the availability of nutrients during cultivation allows macroalgae to be cultivated in integrated systems, which can show a higher growth rate than open sea cultivation, as well as removing approximately 90% of the ammonia available in the system [5]. [PERSON] et al. [3] reported an increase in tissue nitrogen and capacity to absorb ammonia, nitrate, and phosphate by the macroalga _Ulva_ spp. when cultivated in an integrated system on a pilot scale with sea bream (_Sparus aurata_) and sea bass (_Dicentrarchus labrax_). Thus, the insertion of macroalgae into intensive systems with low water exchange can contribute to the reuse of inorganic wastes to form biomass. Biofloc technology (BFT) is an intensive system that allows an increase in the density of organisms and the maintenance of water quality through the growth of microbial communities, such as bacteria, microalgae, and protozoa [6]. The bacteria present can oxidize ammonia to nitrite and subsequently to nitrate or transform ammonia into bacterial biomass [7]. In this system, nitrate and phosphate represent more than 80% of the inorganic compounds produced and accumulated in the system after 42 days of cultivation, according to [PERSON] et al. [8], which is why macroalgae should be included in the system to reuse nutrients. The high availability of nutrients and high organic load present in the biofloc system can alter the nutritional composition of macroalgae. Through of the low light penetration caused by the accumulation of suspended solids [9], macroalgae cultivated in biofloc systems tend to increase chlorophyll \(a\) and \(b\) levels to maximize photosynthesis [10; 11]. In addition to the increase in chlorophyll, _U. lactuca_ macroalgae produced in the biofloc system have a higher protein concentration than those produced in a laboratory solution [12]. This is due to high nutrient availability. Thus, different environments can affect the nutritional value of macroalgae, such as salinities below 25 ppt, which influence the concentrations of amino acids and fatty acids in macroalgae [13]. As a result, the production of macroalga biomass in an integrated system with biofloc, having a high nutritional content, can provide a high-quality product that can be returned to the production system as an additive in the feed of aquatic organisms [14]. Unlike the linear economy, which consists of the production and sale of a product, the circular economy proposal has a wider concept and aims to obtain products or by-products and insert them back into the cultivation system [15]. Therefore, in this practice, the resources produced in the system are reused several times in a closed circuit [16]. The term circular economy reflects the adoption of practices related to the better utilization of the nutrients produced, waste management, and the use of new ingredients to replace feed [17]. This concept has been promoted by the European Commission as a green economy, made applicable to maritime and coastal sectors as a stimulus to new management practices due to limited resources and major environmental impacts, with a focus on providing sustainable aquaculture [18]. According to [PERSON] et al. [19], the production of macroalgae for commercial purposes has a high financial return with increased infrastructure in local communities, especially when associated with integrated production systems. When applied to diets, this production can reduce the commercial feed costs associated with improved performance, as observed by [PERSON] et al. [20]. [PERSON] et al.