DETERMINING THE PHYSIOLOGICAL RESPONSES OF THE MARINE COCCOLITHOPHORE GEPHYROCAPSA HUXLEYI TO NUTRIENT LIMITATION AND TEMPERATURE INTERACTIONS

Marine coccolithophores are calcifying phytoplankton that contribute to both organic carbon fixation through photosynthesis and CaCO₃ production via calcification. Calcification releases CO₂ and the denser CaCO₃ shells enhance carbon export through the ballasting effect, so understanding coccolithophores’ role in the marine carbon cycle is essential, especially under changing environmental conditions. Previous studies have explored individual factor effects on organic and inorganic carbon production, but the interactions of multiple factors remain poorly understood. We examined the responses of the most widespread coccolithophore Gephyrocapsa huxleyi to varying temperatures and nutrient availability by measuring growth, organic carbon fixation, and calcification rates across 6 temperatures under 4 nutrient conditions (replete, N-limited, P-limited, Fe-limited). Our results show that nutrient limitation broadens the optimal temperature range for growth and shifts the balance between calcification and carbon fixation relative to nutrient-replete conditions. N-limited cells had a higher calcification-to-carbon fixation rate ratio at lower temperatures, while P-limited cells showed this at warmer temperatures. Fe limitation strongly reduced the calcification rate relative to the organic carbon fixation rate across all temperatures. These findings suggest that in a warming and increasingly nutrient-depleted ocean, coccolithophore blooms in major nutrient-limited and Fe-limited regimes may contribute very differently to oceanic CO₂ fluxes and carbon export efficiency.

Presentation Preference: Oral

Primary Presenter: Yutong Chen, University of Southern California (yutongc@usc.edu)

Authors:

Yutong Chen, University of Southern California  (yutongc@usc.edu)

Amjad Mansour, University of California Davis  (Aamansour@ucdavis.edu)

Ellya Gholmieh, University of Southern Californica  (egholmie@usc.edu)

Shun-Chung Yang, University of Southern California  (shunchuy@usc.edu)

Xiaopeng Bian, University of Southern California  (xiaopenb@usc.edu)

Seth John, University of Southern California  (sethjohn@usc.edu)

Feixue Fu, University of Southern California  (ffu@usc.edu)

David Hutchins, University of Southern California  (dahutch@usc.edu)