Ulva prolifera green tide in the Yellow Sea of China is a typical cross-regional marine ecological disaster. We hypothesized that the complex interactions between U. prolifera and its associated bacterial communities possibly impact the formation and outbreak of green tide. To test this hypothesis, the U. prolifera-associated bacterial community changes in the entire migration area were investigated through field sampling and high-throughput sequencing. The results showed that (1) with the green tide migration, the richness and diversity increased for U. prolifera epiphytic bacterial communities, while they decreased for seawater bacterial communities in the phycosphere. (2) The richness, diversity, and community composition of U. prolifera-associated bacteria changed more dramatically in the 35.00°N sea area. (3) Potential interactions between bacteria and U. prolifera existed during the entire long-distance migration of green tide, and six bacterial functional groups (BFGs) were defined. Growth-regulating BFG I and antibacterial and stress-resistance BFG II were the dominant communities in the early stage of the green tide migration, which have the role of regulating algal growth and synergistic protection. Heterotrophic BFG III and algicidal BFG IV were the dominant communities in the late stage of the green tide migration, and they were able to compete with algae for nutrients and inhibit algal growth. Nutritive BFG V and algae-derived nutritional type BFG VI symbiotically lived with algal host. Our study highlights the spatial and temporal complexity of U. prolifera-associated bacterial communities and provides valuable insights into the potential contribution of U. prolifera-associated bacterial communities to green tide outbreaks.

黄海石莼绿潮是典型的跨区域海洋生态灾害。我们假设U. prolifera及其相关细菌群落之间复杂的相互作用可能会影响绿潮的形成和爆发。为了验证这一假设，我们通过现场采样和高通量测序研究了整个迁移区域中与美国增殖相关的细菌群落变化。结果表明：（1）随着绿潮迁徙，U. prolifera附生细菌群落的丰富度和多样性增加，而藻类中海水细菌群落的丰富度和多样性下降。(2) 丰富度、多样性和群落组成U. 增殖相关细菌在 35.00°N 海域发生了更显着的变化。(3) 细菌与U. prolifera之间的潜在相互作用在绿潮的整个长距离迁移过程中存在，并定义了六个细菌功能群（BFGs）。调节生长的BFG I和抗菌抗逆BFG II是绿潮迁徙早期的优势群落，具有调节藻类生长和协同保护的作用。异养BFG III和溶藻BFG IV是绿潮迁徙后期的优势群落，能够与藻类竞争养分，抑制藻类生长。营养型 BFG V 和藻类来源的营养型 BFG VI 与藻类宿主共生。我们的研究突出了U. 增殖相关细菌群落的时空复杂性，并提供了对潜在贡献的宝贵见解美国增殖相关细菌群落与绿潮爆发。