Abstract
Short-term ecophysiological and biochemical responses of Cystoseira tamariscifolia and Ellisolandia elongata to changes in solar irradiance and nutrient levels were analyzed in situ in oligotrophic coastal waters by transferring macroalgae collected at 0.5 and 2.0 m depth and exposing them to 2 irradiance levels (100 and 70% of surface irradiance) and nutrient conditions (nutrient-enriched and non-enriched). Both species were affected by changes in irradiance and nutrient levels. Few interactive effects between these 2 physical stressors were found, suggesting major additive effects on both species. C. tamariscifolia collected at 0.5 m and exposed to 70% irradiance had the highest maximal electron transport rate (ETRmax), saturated irradiance (EkETR) and chl a content and the lowest antioxidant activity. Under the same conditions, E. elongata had increased EkETR, antheraxanthin and β-carotene content. At 100% irradiance, C. tamariscifolia collected at 2.0 m had higher maximal quantum yield (Fv/Fm), photosynthetic efficiency (αETR), ETRmax, maximal non-photochemical quenching (NPQmax), saturation irradiance for NPQ (EkNPQ), and antheraxanthin and polyphenol content increased, whereas in E. elongata only αETR increased. In nutrient-enriched conditions, phenolic compounds, several carotenoids and N con- tent increased in C. tamariscifolia at both depths. E. elongata from 2.0 m depth at 100% irradiance and nutrient-enriched conditions showed increased N content and total mycosporine-like amino acids (MAAs). Our results show rapid photophysiological responses of C. tamariscifolia to varia- tions in in situ irradiance and nutrient conditions, suggesting efficient photoacclimation to envi- ronmental changes. In E. elongata, Fv/Fm and ETRmax did not change in the transplant experiment; in contrast, N content, pigment and MAAs (biochemical variables) changed. The responses of these macroalgae to nutrient enrichment indicate oligotrophic conditions at the study site and environmental stress.
Highlights
Environmental stressors can interact and have synergistic or antagonistic effects on physiological responses (Bischof et al 2006)
EC50 in C. tamariscifolia collected at 0.5 m depth showed a significant interaction between nutrients and irradiance
We found high photoacclimation in Cystoseira tamariscifolia and Ellisolandia elongata, with photosynthetic parameters and biochemical composition changing in response to the short-term irradiance and nutrient treatments (60 h)
Summary
Environmental stressors can interact and have synergistic or antagonistic effects on physiological responses (Bischof et al 2006). It is important to understand the mechanisms of combined environmental stressors in order to predict an organism’s responses to future climate scenarios. Benthic intertidal organisms are subjected to major changes during the tidal cycle (Davison & Pearson 1996). The responses of intertidal and benthic organisms to stressors can be very rapid, and involve adjustments in their photosynthetic and respiratory activities (Southward et al 1995, HoeghGuldberg & Bruno 2010, Sorte et al 2010). The algae provide food and shelter, and reduce environmental stress (Davison & Pearson 1996, Jones 1997, Helmuth et al 2002, 2006). The increasing environmental stresses associated with climatic changes and anthropogenic impacts (e.g. coastal eutrophication, increase in UV light) can affect macroalgal communities at the biochemical, ecophysiological, morphological and population levels (Figueroa & Gómez 2001, Bischof et al 2006)
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