Population-specific responses in physiological rates of <i>Emiliania huxleyi</i> to a broad CO<sub>2</sub> range

Abstract

Abstract. Although coccolithophore physiological responses to CO2-induced changes in seawater carbonate chemistry have been widely studied in the past, there is limited knowledge on the variability of physiological responses between populations from different areas. In the present study, we investigated the specific responses of growth, particulate organic (POC) and inorganic carbon (PIC) production rates of three populations of the coccolithophore Emiliania huxleyi from three regions in the North Atlantic Ocean (Azores: six strains, Canary Islands: five strains, and Norwegian coast near Bergen: six strains) to a CO2 partial pressure (pCO2) range from 120 to 2630 µatm. Physiological rates of each population and individual strain increased with rising pCO2 levels, reached a maximum and declined thereafter. Optimal pCO2 for growth, POC production rates, and tolerance to low pH (i.e., high proton concentration) was significantly higher in an E. huxleyi population isolated from the Norwegian coast than in those isolated near the Azores and Canary Islands. This may be due to the large environmental variability including large pCO2 and pH fluctuations in coastal waters off Bergen compared to the rather stable oceanic conditions at the other two sites. Maximum growth and POC production rates of the Azores and Bergen populations were similar and significantly higher than that of the Canary Islands population. This pattern could be driven by temperature–CO2 interactions where the chosen incubation temperature (16 ∘C) was slightly below what strains isolated near the Canary Islands normally experience. Our results indicate adaptation of E. huxleyi to their local environmental conditions and the existence of distinct E. huxleyi populations. Within each population, different growth, POC, and PIC production rates at different pCO2 levels indicated strain-specific phenotypic plasticity. Accounting for this variability is important to understand how or whether E. huxleyi might adapt to rising CO2 levels.

Effects of Elevated CO2 on a Natural Diatom Community in the Subtropical NE Atlantic

“…Recent OA experiments with Calanus glacialis revealed population-specific CO 2 responses with more robust populations found in naturally CO 2 -rich habitats (Thor et al, 2018). These findings suggest that local carbonate chemistry conditions may be a better predictor to assess CO 2 sensitivities of copepods than their taxonomic affiliation (Thor et al, 2018;Zhang et al, 2018). They also suggest that laboratory-based results can only reliably be used to interpret responses observed in experiments with natural assemblages when both experiments were done with individuals from the same population.…”

Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore <i>Emiliania huxleyi</i> under future ocean climate change conditions

“…In all cases, the cells were acclimated to each unique stressor cluster for at least 14-16 generations before physiological and biochemical parameters were measured. Although this stepwise design introduces a historical effect, physiological traits are generally reported after 10 to 20 generations' acclimation to OA treatment (Perrin et al, 2016;Tong et al, 2016;Li et al, 2017), so the historical effects here are similar to those that would be introduced with standard methods in other physiology studies (Tong et al, 2016;Zhang et al, 2019). Since individually reduced availability of nitrate or phosphate decreased growth, did not change the POC quota, and enhanced the PIC quota under optimal light intensity (HL in this study) in the same E. huxleyi strain (Zhang et al, 2019), we hypothesized that the combination of DIN and DIP limitation would result in a similar trend under the pCO 2 and/or temperature combined treatments.…”

“…In the previous work (Zhang et al, 2019), we transferred E. huxleyi cells stepwise from 80 to 120 µmol photons m −2 s −1 , then to 200, to 320 and to 480 µmol photons m −2 s −1 , at both LC and HC levels under HNHP, LNHP or HNLP conditions, respectively. In this study, we transferred the same strain from LL to HL under HNHP conditions, then from HNHP to LNHP or HNLP, and from HNLP to LNLP under HL conditions under four baseline CO 2 and temperature treatments, in an effort to elucidate the interactive and combined effects of temperature, CO 2 , DIN and DIP (Table S2 in the Supplement), in contrast to the previous work carried out under a constant temperature (Zhang et al, 2019).…”

“…The diameter of detected particles was set to be 3 to 7 µm in the instrument, which excluded detached coccoliths (Müller et al, 2012). Cell concentration was also measured by microscopy (Zeiss), and the variation in the measured cell concentration between the two methods was ±7.9 % (Zhang et al, 2019). The average growth rate (µ) was calculated for each replicate according to the equation…”

“…In order to understand the combined effects of pCO 2 , temperature, light, DIN and DIP on functional traits, we incubated Emiliania huxleyi (Lohmann) under different combinations of environmental conditions that represented subsets of, and eventually the complete set of environments for, this environmental driver cluster. We recently examined the interactive effects of light intensity and the CO 2 level on the growth rate and POC and PIC quotas of E. huxleyi under nutrient-replete, low DIN or low DIP concentrations (Zhang et al, 2019). Light, CO 2 , DIN and DIP levels usually change simultaneously with temperature and temperature-modulated responses of E. huxleyi to other environmental drivers (Gafar and Schulz, 2018;Tong et al, 2019).…”