Seasonal interactive effects of pCO 2 and irradiance on the ecophysiology of brown macroalga Fucus vesiculosus L.

• Main Authors: Takolander, Antti, Cabeza, Mar, Leskinen, Elina
• Format: Text
• Language: unknown
• Published: Taylor & Francis 2019
• Subjects: 59999 Environmental Sciences not elsewhere classified; FOS Earth and related environmental sciences; Ecology; FOS Biological sciences; 69999 Biological Sciences not elsewhere classified; Ocean acidification
• Online Access: https://dx.doi.org/10.6084/m9.figshare.8052344.v1; https://tandf.figshare.com/articles/journal_contribution/Seasonal_interactive_effects_of_pCO_sub_2_sub_and_irradiance_on_the_ecophysiology_of_brown_macroalga_i_Fucus_vesiculosus_i_L_/8052344/1

Stochastic upwelling of seawater in the Baltic Sea from the deep, anoxic bottoms may bring low-pH water rich in CO 2 close to the surface. Such events may become more frequent with climate change and ongoing ocean acidification (OA). Photoautotrophs, such as macroalgae, which are important foundation species, have been proposed to benefit from increased carbon availability due to reduced energetic cost in carbon acquisition. However, the exact effects of CO 2 fertilization may depend on the ambient light environment, as photosynthesis rates depend on available irradiance. In this experimental study, interacting effects of CO 2 addition and irradiance on the habitat-forming macroalga Fucus vesiculosus were investigated during two seasons – winter and summer – in the northern Baltic Sea. Growth rates remained unaffected by CO 2 or irradiance during both seasons, suggesting that direct effects of elevated CO 2 on mature F. vesiculosus are small. Increases in CO 2 affected algal elemental ratios by increasing carbon and decreasing nitrogen content, with resulting changes in the C:N ratio, but only in winter. In summer, chlorophyll a content increased under low irradiance. Increases in CO 2 caused a decline in light-harvesting efficiency (decrease in F v /F m and α) under high irradiance in summer, and conversely increased α under low irradiance. High irradiance caused increases in the maximum relative electron transport rate (rETR max ) in summer, but not in winter. Differences between winter and summer indicate that F. vesiculosus responses to CO 2 and irradiance are season-specific. Increases in carbon content during winter could indicate slightly positive effects of CO 2 addition in the long run if the extra carbon gained may be capitalized in growth. The results of this study suggest that increases in CO 2 , either through upwelling or OA, may have positive effects on F. vesiculosus , but these effects are probably small.