Fig 1.
Scheme of the vertical distribution of the studied Antarctic macroalgae coexisting at King George Island indicating the summer light field scenario of relevant solar radiation wavelengths and depth ranges for saturation of photosynthesis (Ek).
Fig 2.
Vertical profile of solar radiation penetration and attenuation coefficients (Kd in m-1) for different wavelengths of UV-B and UV-A radiation and PAR band (400–700 nm).
Values represent average of a representative sunny day at mid-summer (January 2013) at Fildes Bay.
Fig 3.
Variation in photosynthetic parameters (A) ETRmax, (B) initial slope and (C) Ek calculated from electron transport rate based P–E curves of four Antarctic brown collected from three different depths at Fildes Bay.
Values are means ± S.D., n = 4. Asterisks indicate significant difference (p< 0.05) after ANOVA and Tukey HSD post-hoc test.
Fig 4.
Vertical variation in contents of soluble and insoluble phlorotannins (A) and antioxidant capacity (B) determined in extracts of four species of brown algae collected at three different depths at Fildes Bay.
Values are means ± S.D., n = 6–9. Similar letters connect homogeneous means following ANOVA and Tukey HSD post-hoc test.
Fig 5.
Effect of UV radiation on the maximal quantum yield of fluorescence (Fv ⁄ Fm) of four Antarctic algae collected to different depths.
Algae were exposed for 6 h to PAR+UV-A+UV-B (PAR + UV) and PAR conditions (20 μmol m-2 s-1 for PAR, 3 W m-2 for UV-A and 0.25 W m-2), and returned to control culture conditions under dim PAR for 12 h (recovery). Initial is the time cero before the 6 h exposure to UV radiation. Values are means ± S.D., n = 9. The significant decrease in photosynthesis in the UV treatment relative to PAR (ANOVA and Tukey HSD post hoc test) is indicated.
Fig 6.
Effect of UV exposure on the concentration of phlorotannins measured in four brown algae collected at different depth in Fildes Bay.
Algae were exposed for 6 h to PAR+UV-A+UV-B and PAR conditions (20 μmol m-2 s-1 for PAR, 3 W m-2 for UV-A and 0.25 W m-2). Initial is the time cero before the 6 h exposure to UV radiation. Values are means ± S.D., n = 3. Similar letters connect homogeneous mean groups for each species after two-way ANOVA and Tukey’s HSD.
Fig 7.
Effect of UV exposure on the antioxidant capacity measured in four brown algae collected at different depth in Fildes Bay.
Algae were exposed for 6 h to PAR+UV-A+UV-B and PAR conditions (20 μmol m-2 s-1 for PAR, 3 W m-2 for UV-A and 0.25 W m-2). Initial is the time cero before the 6 h exposure to UV radiation. Values are means ± S.D., n = 3. Similar letters connect homogeneous mean groups for each species after two-way ANOVA and Tukey’s HSD.
Fig 8.
Multi-dimensional Scaling Ordinations (MDS) of physiological profiles associated with light use characteristics (A) and UV stress tolerance parameters (B) in relation with depth.
Table 1.
SIMPER analysis of different photosynthetic and biochemical variables measured in four Antarctic brown algae that contribute to the dissimilarity across different depth strata.
Photosynthetic parameters: maximal photosynthesis measured as ETR values; saturation irradiance for photosynthesis (Ek); maximum electron transport rate (ETRmax); initial slope of the ETR-I curve (α); maximum quantum yield (Fv/Fm).
Fig 9.
Relationship between different physiological variables determined in four species of endemic Antarctic brown algae collected at three different depths.