Short-term effects of increasing CO2, nitrate and temperature on three Mediterranean macroalgae: biochemical composition

Short-term effects of increasing pCO2; 380 ppm (LC) vs. 700 ppm (HC); at different nitrogen levels; 5 µM nitrate (LN) vs. 50 µM (HN); on the contents of protein, mycosporine-like amino acids (MAAs), phenolic compounds and total fatty acids, antioxidant activity, calcification and C:N ratios were analyzed in 3 eulittoral Mediterranean macroalgae with different bio-optical characteristics and carbon assimilation efficiencies: Cystoseira tamariscifolia (Heterokontophyta), Ulva rigida (Chlorophyta) and Ellisolandia elongata (Rhodophyta). After acclimation to different pCO2 and nitrogen conditions for 6 d, the algae were subjected to a 4°C temperature increase for 3 d. Increasing temperature and pCO2 produced alterations in the biochemical composition of the 3 macroalgae. Short-term variations of protein levels were observed in U. rigida, with clearly decreased values in the HCLN treatment. In C. tamariscifolia, protein decreased after the temper- ature increase but only under LC. The interaction of temperature and N affected phenolic com- pounds only in U. rigida and the content of MAAs in E. elongata. The functional patterns of the 3 macroalgae in response to the pCO2, nitrogen and temperature regimes may be explained in terms of their bio-optical characteristics and antioxidant activity. The vulnerability and acclima- tion of the 3 species to the expected variations of climate change factors are discussed.