How did the floating Ulva prolifera develop into the world's largest green tide?

It has been 16 years since the world's largest Ulva bloom appeared in the Yellow Sea. However, it remains unclear how the floating Ulva prolifera developed into the immense green tide within two months especially considering that source control measures have been conducted since 2019. In this study, we investigated the growth mechanism of the floating population by examining the production and regeneration of U. prolifera explants and constructing a growth model. The results showed that U. prolifera explants exhibited rapid regeneration mainly through branches at 15, 20 and 25 °C. Algivore feeding and sporulation (at 20–25 °C) contributed to mass production of explants. The growth of floating population could be attributed to the coupling of mass production and rapid regeneration of explants through multiple cycles, which accounted for the outbreak of floating green tide. This finding presented a novel population growth model to elucidate macroalgal bloom occurrences.