Climate change has led to an increase in the frequency of cyclones and wildfire events in tropical regions. However, the combined impact of wildfire particulates and tropical cyclones on marine ecosystems remains uncertain. A micro-experiment conducted at the Yongle Atoll in the South China Sea following Typhoon Noru revealed enhanced phytoplankton growth in response to exposure to total suspended particulates (TSP) from wildfires (2mg/L, 6mg/L) under wind-driven upwelling conditions, with Chl-a concentrations increasing by 3.30 to 5.61-fold. Dinoflagellates accounted for 76% of the variances in Chl-a, while diatoms showed no significant relationship with the Chl-a changes. Additionally, there was an increase in the ratio of diatom-to-dinoflagellate in the upwelling conditions. In contrast, both low and high TSP concentrations led to changes in community structure, including a reduction in the diatom-to-dinoflagellate ratio from 11 to 0.3~0.8 and a significant decline in species diversity at high TSP levels. Eight of these species (6 diatoms and 2 dinoflagellates) were most influential in these community changes. Overall, 66.7% of the dinoflagellate species and 32.1% of the diatom species responded positively to N+N and P. Dissolved inorganic nitrogen and soluble reactive phosphorus explained 52.9% of the species variance. This field study suggests that the dual extreme climatic events of wildfires and tropical cyclones may enhance phytoplankton productivity but may alter phytoplankton community structure, potentially posing a threat to coral reef ecosystems.
 

wildfire aerosols, tropical cyclone, N/P ratio, chlorophyll-a, cpecies diversity, coral reefs