Uso da macroalga vermelha Pterocladiella beachiae na redução de nutrientes do efluente da carcinicultura

Abstract

Marine shrimp aquaculture has shown a rapid growth, standing out the cultivation of the species Litopenaeus vannamei. However, this activity can generate conflicts associated with the release of water rich in nitrogen, phosphorus and suspended solids, in receiving water bodies. The objective of this study was to evaluate the potential of the red macroalgae Pterocladiella beachiae in the removal of nutrients (NH4 + , NO2 - , NO3 - , and PO4 3-) from the shrimp effluent. Three experiments were carried out. In experiment 01, the effluent was collected in a nursery tank, 15 days after shrimp stocking. For experiment 02, the effluent was collected in the same nursery, after 60 days of intensive culture. For the experiment 03, seawater was collected at Meireles Beach (city of Fortaleza, State of Ceará), present in tidal pools in the sandstone reefs. These were transported to the laboratory, washed in running water and removed from the epiphytes. The experimental system 01 and 02 consisted of 16 glass vessels with individual volume of 800 mL, filled with effluent and algae with mean weight (± standard deviation) of 0.44 ± 0.13 and 0.74 ± 0.04 g for experiments 01 and 02, respectively. Experiment 03 used 12 containers with seawater and algae with a mean weight of 0.72 ± 0.03 g. The containers were equipped with constant aeration using airstones, under artificial photoperiod of 12 h. Each week three containers of algae and one control of each experiment were removed for weighing and later discarded, totaling four weeks of cultivation. Results showed a decrease in algae weight of 79, 42 and 20% in experiments 01, 02 and 03, respectively, up to the fourth week. Both the algae and the control presented an efficient removal for the nitrogen compounds, reaching 94.6% of removal, and for the orthophosphate values, the algae presented better removal compared to the control. Only in experiment 02, where the bacteria present were already stable and the nitrification process occurred rapidly, the production of nitrate was greater than the alga could assimilate, resulting in accumulation. However, nitrate concentrations in the algae treatment system were always lower than the control. In conclusion, P. beachiae managed to survive in environments with high turbidity and excess nutrients, but adjustments in experimental systems and better sorting of algae may contribute to better results.