Impact of climate change on frequency and community structure of red tide events in the northern South China Sea

Red tide events are increasingly impacting economies, public health, ecosystems, and aquaculture worldwide, with China experiencing particularly severe effects. This study investigates the changes of red tide events in the Northern South China Sea (NSCS) from 1998 to 2018, focusing on frequency, composition, and environmental drivers. A total of 278 red tide events were reported, with peak in 2003 with 19 events, followed by 14 events in 2004, 9 in 2005, and 7 in 2023. The results indicate that Daya Bay (DYB) is a hotspot for red tide occurrences, with 166 events predominantly caused by Phaeocystis globosa and Noctiluca scintillans. Factors such as thermal discharge and nutrient-rich effluents contribute to the high frequency of red tides in DYB. Other significant locations include Zhanjiang Port (ZJP) with 48 events, Qinzhou Bay (QZB) with 31 events, and Qianjiang Bay (QJB) with 21 events. In contrast, Hongsha Port (HSP) recorded the fewest events, with only 12. The study identified a total of 33 algal species, revealing changes in species composition over the study period. Shifts in dominant species are linked to changing environmental conditions, including rising seawater temperatures and increased nutrient availability. A potential correlation between red tide events and the Nino 3.4 index suggests that global climate patterns may influence red tide occurrences in the NSCS. Additionally, anthropogenic activities, such as industrial wastewater discharge, contribute to the prevalence of red tide events. The study highlights the complex interactions driving red tide blooms in the NSCS and underscores the need for effective management strategies to mitigate their impacts.