History of Harmful Algal Blooms (HABs) in Indonesia: Factors involved in outbreaks in Lampung Bay

In Indonesia, the world’s largest island nation, HABs have been observed since the 1970s, where blooms often occur in eutrophic waters surrounding large population centres (e.g., Ambon Bay, Jakarta Bay, and Lampung Bay). Lampung Bay, in particular, has undergone extensive development and is a major economic hub, hosting a large port and a significant aquaculture industry. Margalefidinium polykrikoides blooms have been recorded in the inner-middle bay and Legundi Island, in the southern part of the bay. Here, we analyse the monitoring data of M. polykrikoides blooms in Lampung Bay from 2012 to 2020 using multivariate analysis (distancebased redundancy analysis). Outbreaks have caused mortality of caged fish including cobia (Rachycentron canadum; at low bloom density; from 103 to 104 cells L-1), pomfret (Trachinotus blochii; moderate bloom; 105 cells L-1), and grouper (Cromileptes altivelis, Epinephelus fuscoguttatus, and E. lanceolatus; dense bloom; >105 cells L-1). Bloom density was strongly correlated with salinity and phosphate (DIP) concentration (P < 0.05), where dense blooms (from 1.68 x 107 to 4.70 x 107 cells L-1) were associated with high DIP (7 - 12 μM) and moderate to high blooms (from 4.34 x 105 to 4.81 x 106 cells L-1) associated with higher salinity (31.8 - 32). In addition, low (from 1.45 x 103 to 2.81 x 104 cells L-1) and moderate (from 3.1 x 104 to 9.5 x 104 cells L-1) bloom density may be influenced by high nitrate, DO, pH, and temperature (P < 0.05). At moderate salinity (31.3 - 31.6), the blooms showed that nitrate and DIP are the dominant macronutrient that limits overall M. polykrikoides density in the bay. This study suggests that M. polykrikoides blooms in Lampung Bay under wide environmental conditions but that cell densities may be regulated by nutrient availability.corresponding author's emails: marianadestilabayu.intan@student.uts.edu.au; mari015@brin.go.i