Heatwave Effects on the Photosynthesis and Antioxidant Activity of the Seagrass Cymodocea nodosa under Contrasting Light Regimes

Global climate change, specifically the intensification of marine heatwaves, affect seagrasses. In Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, particularly during low spring tides. However, photophysiological and antioxidant responses seagrasses to such extreme events are poorly known. Here, we evaluated Cymodocea nodosa exposed at 20 °C 40 150 450 ?mol quanta m?2 s?1. After four-days, analyzed (a) photosynthetic irradiance, maximum photochemical efficiency (Fv/Fm), effective quantum yield photosystem II (?PSII); (b) soluble sugars starch; (c) pigments; (d) (ascorbate peroxidase, APX; oxygen radical absorbance capacity, ORAC, TEAC); oxidative damage (malondialdehyde, MDA). four days °C, C. showed relevant changes in pigments, independent intensity. Increased TEAC APX indicated an “investment” control reactive species levels. Dark respiration starch concentration increased, but sugar concentrations were not affected, suggesting higher CO2 assimilation. Our results show that adjusts its processes successfully handle thermal stress, even under light, draws a promising perspective for resilience change scenarios.