Effects of ocean acidification on marine photosynthetic organisms under the concurrent influences of warming, UV radiation, and deoxygenation

• Published in: Frontiers in Marine Science
• Main Authors: Gao, Kunshan, Beardall, John, Hader, Donat-P., Hall-Spencer, Jason M., Gao, Guang, Hutchins, David A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Algae; Global warming; Hypoxia; Light; Multiple stressors; Nutrients; Phytoplankton; Primary productivity; Ocean acidification
• Online Access: https://research.monash.edu/en/publications/3f4243c9-8620-4167-ac82-714369f67668; https://doi.org/10.3389/fmars.2019.00322; https://researchmgt.monash.edu/ws/files/278077686/278077512_oa.pdf; http://www.scopus.com/inward/record.url?scp=85068564922&partnerID=8YFLogxK

The oceans take up over 1 million tons of anthropogenic CO 2 per hour, increasing dissolved pCO 2 and decreasing seawater pH in a process called ocean acidification (OA). At the same time greenhouse warming of the surface ocean results in enhanced stratification and shoaling of upper mixed layers, exposing photosynthetic organisms dwelling there to increased visible and UV radiation as well as to a decreased nutrient supply. In addition, ocean warming and anthropogenic eutrophication reduce the concentration of dissolved O 2 in seawater, contributing to the spread of hypoxic zones. All of these global changes interact to affect marine primary producers. Such interactions have been documented, but to a much smaller extent compared to the responses to each single driver. The combined effects could be synergistic, neutral, or antagonistic depending on species or the physiological processes involved as well as experimental setups. For most calcifying algae, the combined impacts of acidification, solar UV, and/or elevated temperature clearly reduce their calcification; for diatoms, elevated CO 2 and light levels interact to enhance their growth at low levels of sunlight but inhibit it at high levels. For most photosynthetic nitrogen fixers (diazotrophs), acidification associated with elevated CO 2 may enhance their N 2 fixation activity, but interactions with other environmental variables such as trace metal availability may neutralize or even reverse these effects. Macroalgae, on the other hand, either as juveniles or adults, appear to benefit from elevated CO 2 with enhanced growth rates and tolerance to lowered pH. There has been little documentation of deoxygenation effects on primary producers, although theoretically elevated CO 2 and decreased O 2 concentrations could selectively enhance carboxylation over oxygenation catalyzed by ribulose-1,5-bisphosphate carboxylase/oxygenase and thereby benefit autotrophs. Overall, most ocean-based global change biology studies have used single and/or double stressors in ...