Long-term spatio-temporal analysis of red tides in Hong Kong and their environmental drivers and ecological implications

Red tides, or harmful algal blooms, are a growing concern due to their potential environmental, economic, and health impacts. Nutrient loading and climate change are often cited as the main drivers, but the causes remain inconclusive. The Hong Kong Agriculture, Fisheries and Conservation Department (HKAFCD) has extensive records of red tide sightings (since 1975) and the Hong Kong Environmental Protection Department (HKEPD) has extensive records of environmental data (since 1986). This study examined the spatio-temporal patterns of red tide sightings and their relationship with environmental parameters. The results suggest a change in causative species, with seasonal and spatial influences. The impact of environmental factors on red tide frequency is still unclear. Additionally, the water quality in Hong Kong has improved as a result of the Water Pollution Control Ordinance, Tolo Harbour Effluent Export Scheme (THEES), and implementation of the Harbour Area Treatment Scheme (HATS).