Heterocapsa cf. bohaiensis (dinoflagellate): identification and response to nickel and iron stress revealed through chlorophyll a fluorescence

Metal toxicity in marine ecosystems is a growing issue owing to terrestrial runoff and anthropogenic pollution. Heterocapsa cf. bohaiensis, a newly isolated dinoflagellate from New Caledonia, was cultivated in photobioreactors operating continuously with high concentrations of nickel (1.70 10^-5M) (Ni²⁺) and/or iron (1.79 10^-5M) (Fe²⁺) and their photosynthetic efficiency was assessed. The photosynthetic measurements indicated that H. cf. bohaiensis was tolerant to Ni²⁺ but sensitive to Fe²⁺ high concentrations. In the presence of Fe²⁺, maximum quantum efficiency and maximal relative electron transport rate decreased from 0.62 to 0.47 and from 156 to 102, respectively. The JIP-tests suggested a reduction of the photosynthesis in response to Fe²⁺ due to a disruption in the electron transport chain rather than a defect in the light absorption and trapping capacity which were on the contrary enhanced by Fe²⁺. These results bring new knowledge on the impact of nickel and iron on microalgae photosynthetic pathways.