Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice‐associated diatom compared to a pelagic diatom

Abstract

Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic and sympagic (sea-ice-associated) diatom communities. We investigated the effects of light stress (shift from 20 to 380 µmol photons m À2 s À1 , resembling upwelling or ice break-up) under contemporary and future pCO 2 (400 vs 1000 µatm).The responses in growth, elemental composition, pigmentation and photophysiology were followed over 120 h and are discussed together with underlying gene expression patterns.Stress response and subsequent re-acclimation were efficiently facilitated by T. hyalina, which showed only moderate changes in photophysiology and elemental composition, and thrived under high light after 120 h. In N. frigida, photochemical damage and oxidative stress appeared to outweigh cellular defenses, causing dysfunctional photophysiology and reduced growth. pCO 2 alone did not specifically influence gene expression, but amplified the transcriptomic reactions to light stress, indicating that pCO 2 affects metabolic equilibria rather than sensitive genes.Large differences in acclimation capacities towards high light and high pCO 2 between T. hyalina and N. frigida indicate species-specific mechanisms in coping with the two stressors, which may reflect their respective ecological niches. This could potentially alter the balance between sympagic and pelagic primary production in a future Arctic.

Spatial and Temporal Variability of Ice Algal Trophic Markers—With Recommendations about Their Application

“…Experimental studies with diatom cultures in outdoor aquaria and in situ incubations further confirmed this observation [18,45]. A recent comparison of physiological responses to sudden high light stress in a dominant sea ice diatom with a typical pelagic diatom indicates that the sea ice diatom was strongly negatively affected by high light stress, and hardly recovered over several days [46], whereas its pelagic counterpart was able to successfully acclimate to the new light levels within less than three days. Molecular analyses point towards differences in the antioxidant reaction scheme between the two algal groups, with the sea ice diatom having a less efficient functional response in place.…”

Sea‐ice microbial communities in the Central Arctic Ocean: Limited responses to short‐term pCO2 perturbations

“…The vast majority of ocean acidification studies on sea‐ice microbes have focused on single organisms from Antarctica (reviewed in McMinn 2017) or the Arctic (Torstensson et al 2019; Kvernvik et al 2020), although microbial communities in Southern Ocean brine and bottom ice have recently been investigated (McMinn et al 2017; Castrisios et al 2018; Cummings et al 2019). Our study is the first to report findings on sea‐ice microbial community responses to ocean acidification in the Arctic Ocean and to consider different nutrient regimes.…”

Under-Ice Phytoplankton Blooms: Shedding Light on the “Invisible” Part of Arctic Primary Production

“…This acclimation strategy also enables phytoplankton to adjust quickly to the higher light conditions at ice edges (e.g., leads and polynyas; Palmer et al, 2011;Assmy et al, 2017;Lowry et al, 2018). In particular, pelagic diatoms were found to be able to rapidly acclimate successfully to drastically increased light conditions, in strong contrast to that of sea-ice diatoms (Kvernvik et al, 2020).…”