Sexual reproduction during diatom bloom

Phytoplankton supports food webs in all aquatic ecosystems. Ecological studies highlighted the links between environmental variables and species successions <i>in situ</i>. However, the role of life cycle characteristics on phytoplankton community dynamics remains poorly characterized. In diatoms, sexual reproduction creates new genetic combinations and prevents excessive cell size miniaturization. It has been extensively studied <i>in vitro</i> but seldom in the natural environment. Here, analyzing metatranscriptomic data in the light of the expression patterns previously characterized <i>in vitro</i>, we identified a synchronized and transient sexual reproduction event during a bloom of the toxic diatom species <i>Pseudo-nitzschia australis</i>. Despite the complexity of environmental conditions encountered <i>in situ,</i> sexual reproduction appeared to be the strongest differential gene expression signal that occurred during the bloom. The potential link between environmental conditions and the initiation of sexual reproduction remain to be determined, but sexual reproduction probably had a major impact on the bloom dynamic.