Vulnerability and acclimation of Mediterranean Sea macroalgae, to environmental stress related to climate change: use of indicators physiological state = Vulnerabilidad y aclimatación de macroalgas del Mar Mediterráneo, frente al estrés ambiental derivado del Cambio Climático: uso de indicadores del estado fisiológico

Abstract

In this thesis, the vulnerability and capacity of acclimation to environmental stress related to Climate change mainly in Cystoseira tamariscifolia and other species as Ellisolandia elongata, Cystoseira compressa and Padina pavonica are evaluated. The effects of physical stressors as elevated irradiance of PAR (lambda=400-700 nm) and UVR (lambda=280-400 nm) and temperature and chemical stressors as nutrient, heavy metals and CO2, separately and in interaction with different levels were evaluated. Six experimental studies were conducted under varying irradiance, temperature, nutrient conditions, acidification and heavy metals. The common approach in these studies was the use functional bioindicators to evaluate the physiological state macroalgal species of Mediterranean Sea (Alboran Sea) in studies conducted both in situ in ultra-oligotrophic (Cabo de Gata-Níjar Natural Park, Almeria) and oligotrophic waters (La Araña beach, Malaga) and with algae transported to controlled experimental systems under out-door conditions. In addition, an indoor experiment study was performed in Cystoseira tamariscifolia collected in the North Atlantic Ocean, the northern limit of distribution of this species.

In this study, the decrease of maximal quantum yield and electron transport rate , the increase of phenolic compounds and antioxidant activity or the increase of C:N ratio are produced in stress conditions and thus they are validated as stress indicator. In addition, it is possible to evaluate the direction of the physiological response i.e. positive or negative to expected changes under climate change factors or other anthropogenic impacts, as eutrophication (increased nitrate levels in the water column) or pollution by heavy metals. However, on the other hand, the increase of phenolic compounds is also produced under increased photosynthetic activity showing a link between antioxidant and algal production. This not a strange result since a high photosynthetic activity is related to a high oxygen production which can be produced oxidative stress. Non-photochemical quenching, oxygen consumption through Mehler reaction and increased antioxidant activities are down regulation mechanisms to survive under promoted oxygenic scenario. Phenolic accumulation under increased nitrate and CO2 levels or the release of phenols under increased irradiance in C. tamariscifolia shows us that this species has effective biochemical mechanisms to acclimate for the expected variations in climate change factors although this is limited by temperature. Phenolic compounds are related to secondary metabolism but in C. tamariscifolia but the direct positive relation found

with photosynthetic activity and internal nitrogen in all experiments seem to link the phenols to primary metabolism. In summary, increased CO2 under high irradiance, but not photoinhibitory, conditions will be favorable growth and physiological responses. The nitrate enrichment reduced stress provoked by irradiance or pollution by Cooper due to the photoprotection mechanisms are favored by nitrate increase. However, the positive effect of CO2 and nitrate is dependent on temperature, summer temperature in the field or 4oC increased temperature in outdoor experiments provoked physiological stress. Consequently, ocean acidification will be favorable for C. tamariscifolia only under no very high increase of temperature, less 2-3ºC and without nutrient limitation.

The oligotrophication produced in certain areas of Mediterranean Sea will be unfavorable for Cystoseira tamariscifolia communities in a climate change scenario. The data on vulnerability and acclimation to climate change factors of Cystoseira tamariscifolia, Ellisolandia elongata and Padina pavonica presented in this study can help the management of macroalgal communities, mainly in protected areas. In addition, the physiological and biochemical data will help to predict the effects of climate change on bioactive compounds with antioxidant capacity and their potential biotechnological uses as phenolic compounds, mycosporine like aminoacids and carotenoids.

En esta tesis, se evaluó la vulnerabilidad y la capacidad de aclimatación al estrés ambiental, relacionada al cambio climático, en las especies Cystoseira tamariscifolia, Ellisolandia elongata, Cystoseira compressa y Padina pavonica. En estas especies, se evaluaron los efectos de los factores de estrés físico, como la irradiancia elevada de PAR (lambda = 400-700 nm) y UVR (lambda = 280-400 nm), la temperatura y factores de estrés químico, como nutrientes, metales pesados y CO2. Se realizaron seis estudios experimentales variando irradiancia, temperatura, condiciones de nutrientes, acidificación y metales pesados. El enfoque común en estos estudios fue el uso bioindicadores funcionales como; rendimiento cuántico máximo de PSII (Fv/Fm) como un indicador de estado fisiológico de macroalgas y de la fotoinhibición, la tasa de transporte de electrones (ETR) como un indicador de la capacidad fotosintética. Como indicadores bioquímicos se utilizaron; las relaciones estequiometrias (C:N) como indicador del estado nutricional y el contenido de compuestos fenólicos y micosporinas, tales como sustancias fotoprotectoras y antioxidantes. Con el objetivo de evaluar el estado fisiológico de estas especies de macroalgas en el Mar Mediterráneo (Mar de Alborán). La disminución del rendimiento cuántico y la tasa máxima de transporte de electrones, el aumento de compuestos fenólicos y actividad antioxidante o el aumento de la relación C: N se producen en condiciones de estrés y por lo tanto, estas variables se validan como indicadores de estrés. Sin embargo, se encontró un aumento de los compuestos fenólicos y de la actividad fotosintética, que muestra una relación entre la actividad antioxidante y la producción algal. Este no es un resultado extraño ya que una alta actividad fotosintética se relaciona con una producción alta de oxígeno lo que puede producir estrés oxidativo. La acumulación de compuestos fenólicos en condiciones de aumento de los niveles de nitrato y de CO2 o la liberación de fenoles bajo mayor radiación solar en C. tamariscifolia, nos muestra que esta especie tiene mecanismos bioquímicos eficaces para aclimatarse a las variaciones esperadas en los factores del cambio climático aunque esté limitado por la temperatura.