Evaluation of Floating Net Cage (FNC) in Penerusan Bay, Bali Based on Their Plankton Community

Floating net cages (FNC) are one of the common methods to cultivate fish, in Indonesia, affecting the physicochemical and biological parameters. This study evaluated the water quality conditions in two different FNCs based on the physiochemical and biological parameters. There were four locations to be sampled: two FNC (snappers (KP) and groupers (KR)) and two control sites that were placed outside of FNC (Non-KP and Non-KR). Several water physicochemical parameters were measured, and the plankton community was identified. The observation showed the total suspended solid (TSS) (2.57-2.64 mg/L), pH (8.26-8.3), biochemical oxygen demand (BOD) (0.75-1.52 mg/L) and orthophosphate (P) (0.008-0.044 mg/L). Furthermore, in certain sites, some parameters did not meet the Indonesian Government Standard No. 22 in 2021, including nitrate concentration (KP, Non-KP, and KR), dissolved oxygen (KR and Non-KR), and P (KR and Non-KR). Meanwhile, the phyto- and zooplankton diversity index (H') was 3.61-4.69 and 1.27-2.54, which confirmed that the level of diversity of phyto- and zooplankton was high and moderate status. Four sites showed low phyto- and zooplankton dominance levels and were distributed evenly (E ≥ 0.81). This study concludes that based on water quality parameters, KP and KR did not meet the Indonesian Government Regulation in some parameters, but they had a stable ecosystem based on the phyto- and zooplankton structure community.