Occurrence patterns and causation analysis of Phaeocystis globosa blooms along Guangdong coast over past two decades

Phaeocystis globosa blooms have become one of the typical marine ecological disasters along the Guangdong coast, posing persistent risks to inshore ecological security, mariculture, and cooling water intakes for coastal nuclear power plants. We collected and analyzed data on outbreaks of P. globosa blooms along the Guangdong coast over the past two decades (2005–2024) and investigated the causative factors by examining typical outbreak events in recent years. The results indicate that 47 outbreaks of P. globosa bloom were recorded along the Guangdong coast in the past 20 years, with an annual average of 2.4 events, and 80% of the years had recorded outbreaks. The years 2005, 2007, and 2024 were identified as high-frequency years, and winter was the high-incidence season. The waters of Zhanjiang Port-Donghai Island in western Guangdong and Shanwei Port-Pinqing Lake in eastern Guangdong were high-frequency areas for P. globosa blooms along the Guangdong coast over the years, whereas outbreaks in the Pearl River Estuary in recent years have been characterized by multiple-point, small-scale, and long-duration events. Temperature and nitrate were identified as significant stimulating factors for these outbreaks, and sufficient light is an important condition supporting bloom formation. Diatoms play a driving role in the outbreak of P. globosa blooms, and the competitive advantages endowed by the alga's own diversified carbon-concentrating mechanisms and complex heteromorphic life cycle form the basis for its blooms. Based on the analysis of the patterns and causes of P. globosa blooms along the Guangdong coast, strengthening continuous monitoring in key sea areas during winter and spring, coupled with nutrient input control and coastal ecological environment management, is of significant importance for reducing the risk of P. globosa blooms.