Population dynamics and reproduction of the heterotrophic dinoflagellate Noctiluca scintillans in Jiaozhou Bay, China

Outbreaks of the heterotrophic dinoflagellate Noctiluca scintillans have impacted the Chinese coastal ecosystem for decades; however, which and how environmental factors affect its reproductive pattern and further influence its population dynamics remain to be investigated. From January 2019 to January 2020, 9 cruises were conducted at 12 stations in Jiaozhou Bay, China. The different life stages of N. scintillans were distinguished and quantified with the assistance of microscopic observation and quantitative real-time PCR (qRT-PCR). N. scintillans was seasonally abundant in winter-spring and September, but depleted in summer and October. The asexual reproduction of N. scintillans , which appeared as binary fission, mainly occurred in colder water (<11°C), and could be the major mode of reproduction driving population growth in March-April. In September, even though the asexual mode is by this time restricted by high water temperatures (>26°C), N. scintillans blooms still occurred with the assistance of sexual reproduction and the potential coupling effect of a favorable food source and physical environment, in which chain-forming diatoms were dominant in the phytoplankton community and gametes could be accumulated by continuous mild southeast winds and rainless weather. The present study contributes to a better understanding of the life cycle of N. scintillans in natural seawaters and provides valuable information to assess the variation in the abundance of gametes.