Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer

Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO<sub>2</sub> tolerance in phytoplankton productivity

“…Tolerance to CO 2 levels up to ∼ 800 µatm have been reported for natural coastal communities in the West Antarctic Peninsula and Prydz Bay, East Antarctica (Young et al, 2015;Davidson et al, 2016). Although in Prydz Bay, when CO 2 levels exceeded 780 µatm, primary productivity declined and community composition shifted toward smaller picoeukaryotes Thomson et al, 2016;Westwood et al, 2018). In contrast, Ross Sea phytoplankton communities responded to CO 2 levels ≥ 750 µatm with an increase in primary productivity and abundance of large chain-forming diatoms, suggesting that as CO 2 increases in this region, diatoms may increase in dominance over the prymnesiophyte Phaeocystis antarctica (Tortell et al, 2008b;Feng et al, 2010).…”

“…Bacterial populations respond to increases in phytoplankton primary productivity by increasing their productivity and abundance, with maximum abundance often occurring after the peak of the phytoplankton bloom (Pearce et al, 2007). High CO 2 levels have been observed to have either no effect on abundance and productivity (Grossart et al, 2006;Allgaier et al, 2008;Paulino et al, 2008;Baragi et al, 2015;Wang et al, 2016) or increase growth rate and production only during the postbloom phase of an experiment (Grossart et al, 2006;Sperling et al, 2013;Westwood et al, 2018). Thus, bacterial communities appear to be relatively tolerant to ocean acidification, with bacterial growth indirectly affected by the ocean acidification responses of the phytoplankton community (Grossart et al, 2006;Allgaier et al, 2008;Engel et al, 2013;Piontek et al, 2013;Sperling et al, 2013;Bergen et al, 2016).…”

“…Previous community-level studies investigating the effects of ocean acidification on natural coastal marine microbial communities in East Antarctica reported declines in primary and bacterial productivity when CO 2 levels exceeded 780 µatm (Westwood et al, 2018). To build upon the results of Westwood et al (2018), a similar experimental design was utilised, with a natural marine microbial community from the same region exposed to CO 2 levels ranging from 343 to 1641 µatm in 650 L minicosms.…”

“…To build upon the results of Westwood et al (2018), a similar experimental design was utilised, with a natural marine microbial community from the same region exposed to CO 2 levels ranging from 343 to 1641 µatm in 650 L minicosms. The methods were refined in our study to include an acclimation period to the CO 2 treatment under low light.…”

“…The methods were refined in our study to include an acclimation period to the CO 2 treatment under low light. Rates of primary productivity, bacterial productivity, and the accumulation of particulate organic matter (POM) were examined to ascertain whether the threshold for tolerance to CO 2 was similar to that reported by Westwood et al (2018) or if acclimation affected the community response to high CO 2 . Photophysiological measurements were also undertaken to assess underlying mechanisms that caused shifts in phytoplankton community productivity.…”