Phytoplankton play an important role in marine primary productivity and the cycling of matter and energy flow in marine ecosystems. Many phytoplankton species are causative species for harmful algae blooms. Although many phytoplankton species have been found to develop biogeographic patterns, mechanisms responsible for the development of such biogeographic patterns remain elusive. Recent research on chlorophyll-a uncovered that phytoplankton blooms are modulated by ocean fronts, which are narrow transition zones between distinct water masses. As different phytoplankton species can display differential responses to environmental factors, we hypothesize that different phytoplankton taxa may follow unique biogeographical patterns and be differentially regulated by fronts. Here, the impacts of temperature fronts on phytoplankton composition and their differential biogeographical distribution patterns in the Bohai and Yellow Seas were investigated using metabarcoding analysis, which enabled the identification of phytoplankton taxa at high resolution. Clear geographic distribution patterns of the phytoplankton community structure were identified. Distance-decay analysis showed that the phytoplankton communities were significantly correlated with environmental distance and geographical distance. In addition, geographic distribution pattern of phytoplankton was also shaped by their correlations with other plankton species. Integrated analyses demonstrated that temperature fronts could form transition zones with high richness and chlorophyll-a concentrations, physical barriers delimiting independent distribution of phytoplankton community, as well as chemical factors, among different water masses. Overall, this study uncovered high molecular diversity and clear geographic pattern of phytoplankton communities, highlighting that temperature fronts serve as the driving force for the distributions and assembly of phytoplankton community.

Bohai and Yellow Seas, temperature fronts, metabarcoding analysis, co-occurrence network