Effects of elevated pCO₂ on the response of coccolithophore Emiliania huxleyi to prolonged darkness

ABSTRACT

Although numerous studies have examined the responses of coccolithophores to ocean acidification, less is known on the fate of those calcifying organisms when they sink to the ocean’s aphotic regions. In this study, the coccolithophore Emiliania huxleyi was first grown under a regular 12/12 light/dark cycle at 20°C, exposed to both high (1000 μatm) and ambient CO₂ (410 μatm) levels. The cultures were then transferred to continuous darkness for 96 h at 20°C or 16°C. We found that elevated CO₂ decreased the specific growth rate while increasing the cellular particulate organic carbon (POC) and nitrogen (PON) contents and the POC/PON ratio of E. huxleyi in the light/dark period. After 96 h of dark acclimation, the cell abundance decreased more obviously at 20°C than at 16°C but showed no significant difference between the two CO₂ treatments. The decrease in volumetric POC concentration was most prominent in the high CO₂/20°C treatment and least in the ambient CO₂/16°C treatment. At 16°C, the PON concentration increased in the high CO₂ cultures and exhibited no change in the ambient CO₂ cultures. While at 20°C, the PON concentration decreased significantly both under high and ambient CO₂ conditions. The final POC/PON ratio showed no significant differences among the different temperature and CO₂ treatments. Overall, a higher percentage of POC relative to that of PON was lost in darkness with increasing CO₂ concentration, with potential implications for the ocean’s nutrient cycle.

KEYWORDS:

• Coccolithophore
• ocean acidification
• carbon cycling

Acknowledgements

This work was supported by National Natural Science Foundation of China under Grant 42006117 and 32072997, Natural Science Foundation of Shandong Province under Grant ZR2020QC042 and Talent Induction Program for Youth Innovation Teams in Colleges and Universities of Shandong Province (2022–2024).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Natural Science Foundation of China under Grant 42006117 and 32072997, Natural Science Foundation of Shandong Province under Grant ZR2020QC042 and Talent Induction Program for Youth Innovation Teams in Colleges and Universities of Shandong Province (2022–2024).