Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; under future ocean climate change conditions

Yong Zhang,Sinéad Collins,Kunshan Gao

doi:10.5194/bg-17-6357-2020

Abstract

Abstract. Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on the growth rate, particulate organic carbon (POC) and particulate inorganic carbon (PIC) quotas of the cosmopolitan coccolithophore Emiliania huxleyi. The population growth rate increased with increasing temperature (16 to 20 ∘C) and light intensities (60 to 240 µmolphotonsm-2s-1) but decreased with elevated pCO2 concentrations (370 to 960 µatm) and reduced availability of nitrate (24.3 to 7.8 µmol L−1) and phosphate (1.5 to 0.5 µmol L−1). POC quotas were predominantly enhanced by the combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected the growth, photosynthetic carbon fixation and calcification of E. huxleyi and imply that plastic responses to progressive ocean acidification, warming, and decreasing availability of nitrate and phosphate reduce the population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

Highlights

Ocean acidification (OA), due to continuous oceanic absorption of anthropogenic CO2, is occurring alongside ocean warming
We found that future ocean scenario treatments with OA, warming, increased light and reduced availability of nutrients led to a lower growth rate and larger particulate organic carbon (POC) and particulate inorganic carbon (PIC) quotas of E. huxleyi
Seawater pCO2 concentrations decreased by 8.8 % ± 1.1 % in low pCO2 + low temperature (LCLT), by 6.1 % ± 4.4 % in high pCO2 + low temperature (HCLT), by 6.6 % ± 1.7 % in low pCO2 + high temperature (LCHT), and by 5.4 % ± 3.6 % in high pCO2 + high temperature (HCHT) conditions (Fig. 1k–o; Table 1)

Summary

Introduction

Ocean acidification (OA), due to continuous oceanic absorption of anthropogenic CO2, is occurring alongside ocean warming. While most studies on the effects of ocean global climate changes on marine primary producers have focused on organismal responses to one, two or three environmental drivers, there is an increasing awareness of the need to measure the combined effects of multiple drivers (see reviews by Riebesell and Gattuso, 2015; Boyd et al, 2018; Gao et al, 2019; Kwiatkowski et al, 2019) For this purpose, several manipulative experimental approaches have been recommended (Boyd et al, 2018).

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Results

Conclusion