Cell size as a biomarker for proliferation in Noctiluca scintillans: Insights from controlled experiments

Harmful algal blooms (HABs) present increasingly threaten marine ecosystems on a global scale. Noctiluca scintillans, a globally prevalent dinoflagellate, frequently forms HABs characterized by substantial fluctuations in cell size linked to growth and division. To understand how environmental factors modulate these dynamics, we investigated the effects of prey availability, prey type, temperature, and light-dark cycles on the growth and cell size of N. scintillans under controlled laboratory conditions. It was observed that binary cell division occured mostly during dark-to-light transitions, with division resulting in marked reductions in cell diameter. Optimal proliferation was observed at 20-25 °C with sufficient prey, and higher growth rates consistently corresponded to smaller mean cell sizes. In accordance, cells in exponential growth were notably smaller than those in stationary phase. A significant inverse relationship between cell size and growth rate was quantified (Cell size = -617.1 × Growth rate + 485.1; R² = 0.53, p = 0.005). These findings highlight the potential of cell size as an indicator of growth rate and establish a foundation for developing size-based monitoring strategies to enhance N. scintillans bloom prediction.