Articles | Volume 13, issue 24
Biogeosciences, 13, 6625–6635, 2016

Special issue: Effects of rising CO2 on a Baltic Sea plankton...

Biogeosciences, 13, 6625–6635, 2016

Research article 16 Dec 2016

Research article | 16 Dec 2016

Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea

Rafael Bermúdez1,2, Monika Winder3, Annegret Stuhr1, Anna-Karin Almén4, Jonna Engström-Öst4,5, and Ulf Riebesell1 Rafael Bermúdez et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Facultad de Ingeniería Marítima, Ciencias Biológicas, Oceánicas y Recursos Naturales, Escuela Superior Politécnica del Litoral, ESPOL, Guayaquil, Ecuador
  • 3Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden
  • 4Novia University of Applied Sciences, Coastal Zone Research Team, Ekenäs, Finland
  • 5Tvärminne Zoological Station, University of Helsinki, J.A. Palménin tie 260, 10900 Hanko, Finland

Abstract. Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations ( ∼  347 µatm fCO2) up to values projected for the year 2100 ( ∼  1333 µatm fCO2). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO2. Although this coastal plankton community was tolerant of high pCO2 levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.

Short summary
Increasing CO2 is changing seawater chemistry towards a lower pH, which affects marine organisms. We investigate the response of a brackish plankton community to a CO2 gradient in terms of structure and fatty acid composition. The structure was resilient to CO2 and did not diverge between treatments. FA was influenced by community structure, which was driven by silicate and phosphate. This suggests that CO2 effects are dampened in communities already experiencing high natural pCO2 fluctuation.
Final-revised paper