Localization and antioxidant capacity of flavonoids in Halophila johnsonii in response to experimental light and salinity variation

► We examine physiological role of flavonoids in H. johnsonii. ► We examine antioxidant and flavonoid responses to light and salinity variations. ► Results suggest flavonoids may perform antioxidant functions. ► Hyposalinity combined with shading can reduce photosynthesis of H. johnsonii.