Potential use of the macroalgae Ulva spp. integrated to the cultivation of shrimp maintained in a biofloc system
The use of production systems without water renewal, such as the Biofloc system (BFT), results in the accumulation of nitrogenous and phosphate products throughout the cultivation. To avoid problems with water quality, an alternative is the adoption of Integrated Multitrophic Aquaculture (IMTA), which provides the use of these residues by organisms of different trophic levels. Macroalgae, as excellent and economically important biofilters, are important constituents of these systems. Therefore, this work aims to determine the viability of integrated multitrophic cultivation between shrimp (Litopenaeus vannamei) and macroalgae (Ulva flexuosa and Ulva fasciata) in a biofloc system, evaluating the effects of total suspended solids (TSS) on macroalgae, its nutrient absorption and better density. For this, the first two experiments evaluated the growth and protein content of macroalgae U. fasciata and U. flexuosa cultivated in recirculating water of a shrimp culture in BFT system at different concentrations of SST and in chemical solution von Stosch and PES (Provasoli's Enrichment Solution) and their protein concentrations. In the third experiment, the performance in nutrient absorption and growth of macroalgae in integrated cultivation with L. vannamei was tested. And finally, in the fourth experiment, different density of U. fasciata were tested in integrated cultivation with L. vannamei, seeking to optimize the nutrient absorption process. Experiments 01 and 02 took place in a laboratory with 35 and 17 days of cultivation, respectively, in plastic containers. Experiments 03 and 04 took place in an agricultural greenhouse, operating with 35 days of cultivation in boxes with a useful volume of 150L and constant aeration. The physical and chemical parameters of water quality and nutrients were analyzed: total ammonia nitrogen, nitrite, nitrate and phosphate. Shrimp biometrics and macroalgae weighing occurred weekly. Shrimp were fed twice a day (Guabi 38% CP, 1.6mm). We saw that macroalgae cultivated in biofloc effluents obtained higher protein concentrations in their tissues and the same growth as those cultivated in von Stosch and PES solution, showing that total suspended solids concentrations between 400 and 650 mg/L do not affect their performance. When integrated into shrimp cultivation, the macroalgae U. fasciata showed better absorption of nitrate in the cultivation and final biomass of 202.67 ± 53.67g, superior to U. flexuosa. Finally, the initial density of 1g/L of U. fasciata obtained the best result in the removal of nitrate. The integrated multitrophic cultivation of L. vannamei with the macroalgae U. fasciata proved to be viable and promising in the absorption of nutrients, in the improvement of water quality parameters and in the production of plant biomass with added value, opening up opportunities for the realization of an aquaculture more sustainable.