Dinoflagellates are key marine primary producers whose responses to combined stressors remain limited understanding. Oxyrrhis marina, a cosmopolitan heterotrophic dinoflagellate tolerant of variable coastal conditions, provides a useful model for assessing the interactive effects of polycyclic aromatic hydrocarbons (PAHs) and ultraviolet (UV) radiation. This study aims to quantify how PAHs type and concentration, together with varying UV intensities, influence the growth, survival, and physiology of O. marina. Cultures of O. marina, initially fed Isochrysis galbana, are exposed in f/2 medium to 3 kinds of  representative PAHs (Naphthalene, Phenanthrene, Pyrene) at 0μg L⁻¹, 50μg L⁻¹, 500μg L⁻¹, and 2000 μg L⁻¹ under low, medium, and high UV regimes (UVA: 0.3–2.5 W m⁻²; UVB: 0.1–1.0 W m⁻²). UV levels are manipulated using controlled lamp distance and UV-screening materials. Cells abundance and net growth rates are determined periodically, and prey ingestion rates are estimated using established grazing models. PAHs concentrations in water and algal pellets are quantified by GC/MS. Cellular stress is evaluated by measuring intracellular reactive oxygen species (ROS) via 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescence and antioxidant responses through superoxide dismutase (SOD) activity.
  Based on current experimental results, the control group showed very rapid growth. Using day 3 and day 7 as the time intervals for calculation, the growth rate of Oxyrrhis marina reached 0.5278d-1, the average density of prey algae (Isochrysis galbana,) during the growth period was 76,000 cells/mL, and the feeding rate was 4.3742cells⋅ind-1⋅d-1. In the ongoing multi-factor stress experiment, the results from day 0 and day 3 show that the higher the concentration of naphthalene, the greater the inhibition of Oxyrrhis marina growth; simultaneously, due to the higher level of UV radiation, the growth of both Oxyrrhis marina and Isochrysis galbana, was affected, and the inhibition became stronger with increasing naphthalene concentration. These preliminary experimental results still need to be verified by subsequent experiments over a period of time.

 

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