The Effectiveness of Gracilaria sp. as a Biofilter in Reducing Aquaculture Waste Based on Planting Location in the Waters of Ujung Betok, East Lombok

Abstrak

Aquaculture waste can increase dissolved inorganic nutrient concentrations, making seaweed-based treatment an important component of integrated biological nutrient management. This study aimed to evaluate strategic planting locations of Gracilaria sp. around floating net cages and assess its effectiveness as a natural biofilter for reducing nitrogenous waste in Ujung Betok waters, East Lombok. A Completely Randomized Design (CRD) was applied with three planting-distance treatments and three replicates. Total Ammonia Nitrogen (TAN) concentrations ranged from 0.29–0.31 mg/L at the beginning and 0.24–0.29 mg/L at the end of the 30-day culture period. ANOVA showed no significant difference in initial TAN among treatments (p = 0.868), whereas final TAN differed significantly among planting locations (p = 0.001). Final total nitrogen content in Gracilaria sp. tissue ranged from 0.287–0.330%, with the highest value in T2 (0.330 ± 0.050%), followed by T3 (0.303 ± 0.006%) and T1 (0.287 ± 0.015%). Planting location did not significantly affect tissue total nitrogen content (p > 0.05). Tissue nitrogen reduction was 13.03% in T1, 0.00% in T2, and 8.18% in T3. TAN reduction was highest in T1, decreasing from 0.31 to 0.24 mg/L or 22.58%, followed by T2 at 3.33%, while T3 showed no reduction. These results indicate that Gracilaria sp. can contribute to nitrogen removal, with the 25 m planting location showing the best biofiltration performance.