The effects of a marine heatwave on seagrasses cymodocea nodosa and zostera marina in Ria Formosa, Portugal: photosynthetic activity & oxidative stress indicators

• Main Author: Deguette, Alizé
• Publication Date: 2021
• Format: Master thesis
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10400.1/19805
• topic: Marine Heatwave; Heat stress; Clorophyll fluorescence; Ria Formosa; Zostera marina; Cymodocea nodosa

Seagrasses play a high ecological role and provide a large range of ecosystem services, yet they are globally threatened by climate change. The seagrasses Zostera marina and Cymodocea nodosa share the same ecological niche in Ria Formosa, Southern Portugal, where their thermal distribution limits meet. While C. nodosa has its northern distribution limit in Portugal, Z. marina reaches its southern distribution limit in Ria Formosa. The present work aims to comparatively evaluate the physiological responses of both species to marine heatwaves (MHWs), a phenomenon that is increasing in frequency and intensity with climate change. Shoots of both species were transplanted into a mesocosm experiment where a MHW was simulated. The heatwave design was composed of a heating ramp from 20 to 28 °C, a 7-days heatwave at 28 °C, followed by a cooling ramp and an 8-days recovery period at 20 °C. The potentially stressful effects of the MHW on the plant’s physiology were investigated, both during the MHW peak and after recovery. Photosynthetic performance was assessed with photosynthesis-irradiance (P-I) curves parameters (α, Pm and Ik) and chlorophyll fluorescence imaging (CFI). Complementarily, key biochemical stress indicators (Total phenols, TEAC, ORAC, MDA) were quantified to investigate the oxidative stress level in plant tissues. Only C. nodosa survived the acclimation period. The maximum quantum yield of photosystem II (ΦPSII) was enhanced during the heatwave, probably to maintain the photosynthetic activity at control level. Negative effects on the photosynthetic performance of C. nodosa were observed after recovery, whereas ΦPSII came back to control level. No significant oxidative stress was observed all along the experiment. Overall, although C. nodosa showed a relatively high tolerance to MHWs compared to other species such as Z. marina, C. nodosa population in Ria Formosa is likely to be negatively affected by the forecasted climate change scenarios.