The expansion of Ulva prolifera O.F. Müller macroalgal blooms in the Yellow Sea, PR China, through asexual reproduction

- Four different growth and reproductive strategies of U. prolifera segments were discovered.
- Polarized growth is one of the most important developmental pathways for U. prolifera segments.
- Formation of many bladelets from a single segment may enhance the rapid growth of the macroalgal blooms.

Since 2007, Ulva macroalgal blooms have occurred along the coastal areas of the Yellow Sea, China. These blooms are dominated by fragments of Ulva prolifera in the early stages of development. The objectives of this study were to identify the primary mode of asexual reproduction for U. prolifera and to evaluate the contribution of these thalli fragments to the formation of blooms. Four different growth and reproductive strategies of U. prolifera segments were found including: 1) tubular diameter becoming larger; 2) formation of new branches; 3) release of zoids; and 4) polarized growth. This is the first report showing the development of numerous blade-lets from a single segment, which is remarkably different from previous studies on other Ulva species. The results in the present study provide critical information to understand how this species is able to support its explosive growth during a bloom.