Trophic state assessment of marine ecosystems used for floating net cage aquaculture: a case study in Pegametan Bay, North Bali, Indonesia

This study aimed to assess the trophic status of Pegametan Bay, Bali, Indonesia, as influenced by floating net cage aquaculture activities during June 2019 (dry season) and March 2021 (wet season). The trophic status was assessed using 24 parameters developed from a literature review, and water samples were collected from four observation stations. Data were analyzed using field measurements and laboratory analyses. The results showed that dissolved oxygen ranged between 2.6–9.1 mg/l in June 2019 and 3.4–7.7 mg/l during the March 2021 measurement period, salinity (33.6–34.4 ppt and 31–34 ppt), turbidity (0.77–6.33 FNU and 1.2–3.42 FNU), water clarity (4.18–11.92 m and 4.44–8.44 m), Biological Oxygen Demand (10.5–26 mg/l and 1–17 mg/l), Chemical Oxygen Demand (3.68–11 mg/l and 15.5–46.5 mg/l), chlorophyll-a (0.11–0.24 mg/l and 0–0.56 mg/l), Total Dissolved Solids (20,400–22200 mg/l and 21,300–53400 mg/l), ammonia (0.038–0.178 mg/l and 0.01–0.3 mg/l), nitrate (0.02–0.706 mg/l and 0.01–0.03 mg/l), orthophosphate (0.014–0.174 mg/l and 0.04–1.59 mg/l, and culturable bacteria (0–1.74 ∙ 105 CFU/mL and 0–1.61 ∙ 108 CFU/mL). Pegametan Bay exhibited a significant decrease in water quality between June 2019 and March 2021, with mesotrophic and eutrophic trophic states. The parameters determining changes in the trophic state of Pegametan Bay were orthophosphate, TSS, organic content, E. coli, Salmonella, and Vibrio. This trophic state assessment can be used for early detection, monitoring, water quality control, and eutrophication control, thereby ensuring sustainable aquaculture activities and optimal marine resource production.