Climate Change Drives Long-Term Spatiotemporal Shifts in Red Noctiluca scintillans Blooms Along China's Coast.

Climate change has significantly altered the spatiotemporal distribution and phenology of marine organisms, yet the long-term trends and mechanisms driving these changes remain insufficiently understood. In this study, we analysed historical Noctiluca scintillans bloom data from coastal China (1933, 1952, 1981-2023), sea surface temperature (SST) records from the past 40 years, and 509 field samples using Single Molecule Real-Time (SMRT) sequencing (2019-2024). Our results indicate that SST is the primary driver of N. scintillans blooms, exhibiting a nonlinear unimodal correlation. Long-term SST warming has caused a northward shift in bloom locations, aligning with the 21.9°C-22.7°C isotherms, as reflected by the increasing average latitudes of bloom occurrences. Over the past 4 decades, bloom frequency and duration have followed an overall increasing trend, displaying an approximate 10-year cyclical pattern. Ocean warming has also contributed to earlier bloom initiation, extended peak bloom periods and delayed bloom termination, shaping the long-term dynamics of N. scintillans blooms. SMRT sequencing confirmed that local N. scintillans populations persist year-round, serving as latent seed sources that can rapidly bloom when environmental conditions become favourable. These findings provide critical insights into the dynamics of harmful algal blooms in the context of climate change and lay a foundation for future ecological and environmental research.