Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula

Abstract

The Western Antarctic Peninsula (WAP), one of the most productive regions of the Southern Ocean, is currently undergoing rapid environmental changes such as ocean acidification (OA) and increased daily irradiances from enhanced surface-water stratification. To assess the potential for future biological CO 2 sequestration of this region, we incubated a natural phytoplankton assemblage from Ryder Bay, WAP, under a range of pCO 2 levels (180 μatm, 450 μatm, and 1000 μatm) combined with either moderate or high natural solar radiation (MSR: 124 μmol photons m −2 s −1 and HSR: 435 μmol photons m −2 s −1 , respectively). The initial and final phytoplankton communities were numerically dominated by the prymnesiophyte Phaeocystis antarctica, with the single cells initially being predominant and solitary and colonial cells reaching similar high abundances by the end. Only when communities were grown under ambient pCO 2 in conjunction with HSR did the small diatom Fragilariopsis pseudonana outcompete P. antarctica at the end of the experiment. Such positive light-dependent growth response of the diatom was, however, dampened by OA. These changes in community composition were caused by an enhanced photosensitivity of diatoms, especially F. pseudonana, under OA and HSR, reducing thereby their competitiveness toward P. antarctica. Moreover, community primary production (PP) of all treatments yielded similar high rates at the start and the end of the experiment, but with the main contributors shifting from initially large to small cells toward the end. Even though community PP of Ryder Bay phytoplankton was insensitive to the changes in light and CO 2 availability, the observed size-dependent shift in productivity could, however, weaken the biological CO 2 sequestration potential of this region in the future.

Ocean acidification and high irradiance stimulate the photo-physiological fitness, growth and carbon production of the Antarctic cryptophyte <i>Geminigera cryophila</i>

“…Even though most studies on temperate cryptophytes report a photo-protective function of Allo, with higher amounts of this carotenoid toward high irradiance (Funk et al, 2011;Laviale and Neveux, 2011), the reduction in cellular Allo quotas from LL to ML in our tested species (Table 2) rather suggests its role in light absorption. Similarly, cellular Allo contents also declined between 40 and 100 µmol photons m −2 s −1 in the temperate cryptophyte Rhodomonas marina (Henriksen et al, 2002). In this study, various photo-physiological parameters (P , σ PSII , τ Q a , Fig.…”

“…1). Compared with the Antarctic diatoms and P. antarctica tested so far, which exhibited either negative or neutral effects in response to OA and high irradiance on growth and/or photo-synthesis (Feng et al, 2010;Heiden et al, 2016Heiden et al, , 2019Trimborn et al, 2017a, b;Koch et al, 2019), growth and photosynthesis of the cryptophyte benefitted synergistically from OA and HL. Looking at the significantly higher amounts of Chl a and Allo per cell and its larger σ PSII between ML and HL under OA (Table 2, Fig.…”

“…For various Antarctic diatoms and the prymnesiophyte P. antarctica, growth and/or carbon fixation remained unaltered by OA alone (Riebesell et al, 1993;Boelen et al, 2011;Hoogstraten et al, 2012;Trimborn et al, 2013;Hoppe et al, 2015;Heiden et al, 2016). Recent studies suggest that Southern Ocean diatoms are more prone to OA especially in conjunction with high light than the prymnesiophyte Phaeocystis antarctica (Feng et al, 2010;Trimborn et al, 2017a, b;Beszteri et al, 2018;Heiden et al, 2018Heiden et al, , 2019Koch et al, 2018). The response of cryptophytes to OA is hitherto almost unexplored.…”

Impacts of Temperature, CO2, and Salinity on Phytoplankton Community Composition in the Western Arctic Ocean

“…Negative interactive effect of higher CO 2 and light levels on two Antarctic diatom isolates have observed but it was not evident for prymnesiophyte Phaeocystis antarctica (Trimborn et al, 2017). In contrast, higher light intensity diminished the negative impact of high CO 2 levels on the productivity of Antarctic phytoplankton community (Heiden et al, 2019). In the present study, although the PAR levels were about three times higher in the MR16exp., the fertilization effect of higher CO 2 levels on the growth rate of many non-diatom phytoplankton appeared only in the MR16-exp.…”

Ocean acidification and high irradiance stimulate growth of the Antarctic cryptophyte <i>Geminigera cryophila</i>

“…connectivity, p), functional absorption cross section of PSII photochemistry recovery were determined for Geminigera cryophila acclimated to ambient or high CO 2 conditions combined with low (LL), medium (ML) or high light (HL). G. cryophila did not grow under5 ambient pCO 2 and HL as indicated by ng. Photosynthetic parameters were derived from at least three independent measurements.…”