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

Abstract

<p><strong>Abstract.</strong> Increasing atmospheric carbon dioxide (CO<sub>2</sub>) is changing seawater chemistry towards reduced pH, which consequently 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 CO<sub>2</sub> and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO<sub>2</sub> 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 off-shore mesocosms and subjected to a CO<sub>2</sub> gradient ranging from natural concentrations (~347 μatm <i>p</i>CO<sub>2</sub>) up to values projected for the year 2100 (~1333 μatm <i>p</i>CO<sub>2</sub>). We show that the phytoplankton community composition was resilient to CO<sub>2</sub> 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 CO<sub>2</sub> treatments. These results suggest that CO<sub>2</sub> effects are dampened in coastal communities that already experience high natural fluctuations in <i>p</i>CO<sub>2</sub>. Although this coastal plankton community was tolerant to high <i>p</i>CO<sub>2</sub> levels, hypoxia and CO<sub>2</sub> uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.</p>

Predictable ecological response to rising CO2 of a community of marine phytoplankton

“…Studies of natural assemblages of marine phytoplankton have found that high CO 2 resulted in an increase in the abundance of the cyanobacterium Synechococcus and a decrease in the abundance of the coccolithophore Emiliania huxleyi (Paulino, Egge, & Larsen, ). Similar experiments also found a decrease in fucoxanthin‐containing phytoplankton including diatoms (Yoshimura et al., ) or that community composition remains unchanged (Bermúdez et al., ). Within taxonomic groups, an increase in CO 2 benefits larger over smaller diatoms (Tortell et al., ) as expected from facilitation of CO 2 diffusion with larger surface area to volume ratios.…”

Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

“…For more detailed descriptions of the primary variables and the different methods used during this CO 2 mesocosm campaign, we refer to other papers in this joint volume: i.e., total particulate carbon (TPC), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) are described by Paul et al (2015); micro-and nanophytoplankton enumeration by Bermúdez et al (2016); picophytoplankton, heterotrophic prokaryotes, and viruses by Crawfurd et al (2016); zooplankton community by Lischka et al (2015); primary production and respiration by Spilling et al (2016a); BP by Hornick et al (2016); and sedimentation by Boxhammer et al (2016) and Paul et al (2015).…”

Effect of elevated CO<sub>2</sub> on organic matter pools and fluxes in a summer Baltic Sea plankton community

“…: every 4th day until t29; copepods: weekly (t3, t10, t17, t24, t31, t38) Almén et al (2015); Bermúdez et al (2015) Fatty acid concentrations (E. affinis adults and eggs from reproduction incubations)…”