| Summary: | Identifying adaptive or mitigating solutions for climate change is especially important for high conservation value ecosystems, such as kelp forests. The effects of Marine Heatwaves (MHWs), short-term increased temperature events, on the physiology of such organisms have been greatly overlooked when addressing thermal stress impacts, with a greater attention given to ocean warming. By testing the combined effect of heatwaves and ocean acidification, it has been demonstrated that the extra Carbon source helped organisms on their resilience to the thermal stressor, yet the effect extra light sources could have has never been analysed. In this study the combined effect of MHWs (+3ºC) and Artificial Light at Night (ALAN) (24hlight-0h dark), exposure was tested on the photosynthetic parameters (Fv, Fv/Fm, ETRm and Alfa), growth and respiration (R) rates and C/N tissue ratio of the species Laminaria digitata. A 14-day MHW simulation was performed followed by a 10-day recovery period, in short term mesocosm experiments at the Plymouth Marine Laboratory. A “collapsed factorial design”, was used with “SW Temperature” set as the main driver and “Light availability nested within SW Temperature” as the secondary one. As expected MHW alone caused significant negative impacts on growth and C/N tissue ratios, with organisms presenting the lowest rates, even in the recovery period, while it increased their fluorescence responses, with the highest’s values of Fv and Fv/FM observed only during the exposure period. On the other hand, MHW combined with ALAN treatments showed the highest values of growth and C/N ratios, while presenting the lowest values of Alfa, due to down regulations of light consumption mechanisms. It was concluded that by exposing organisms to ALAN this could help them on their resilience to MHW events, by enhancing their carbon fixation rates, and hence producing the extra amount of energy necessary to withstand the thermal stressor. No atual contexto das mudanças ambientais observadas a nível global, ...
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