A comparison of species specific sensitivities to changing light and carbonate chemistry in calcifying marine phytoplankton

Abstract

Coccolithophores are unicellular marine phytoplankton and important contributors to global carbon cycling. Most work on coccolithophore sensitivity to climate change has been on the small, abundant bloom-forming species Emiliania huxleyi and Gephyrocapsa oceanica . However, large coccolithophore species can be major contributors to coccolithophore community production even in low abundances. Here we fit an analytical equation, accounting for simultaneous changes in CO 2 and light intensity, to rates of photosynthesis, calcification and growth in Scyphosphaera apsteinii . Comparison of responses to G. oceanica and E. huxleyi revealed S. apsteinii is a low-light adapted species and, in contrast, becomes more sensitive to changing environmental conditions when exposed to unfavourable CO 2 or light. Additionally, all three species decreased their light requirement for optimal growth as CO 2 levels increased. Our analysis suggests that this is driven by a drop in maximum rates and, in G. oceanica , increased substrate uptake efficiency. Increasing light intensity resulted in a higher proportion of muroliths (plate-shaped) to lopadoliths (vase shaped) and liths became richer in calcium carbonate as calcification rates increased. Light and CO 2 driven changes in response sensitivity and maximum rates are likely to considerably alter coccolithophore community structure and productivity under future climate conditions.

Particulate inorganic to organic carbon production as a predictor for coccolithophorid sensitivity to ongoing ocean acidification

“…The influence of average cell size, cell volume, and surface area to volume ratio (calculated from Table ) on OA sensitivity was also examined. Fit coefficients for G. oceanica , E. huxleyi , and S. apsteinii were taken from Gafar et al (), Gafar and Schulz (), and N. A. Gafar et al (). Fit coefficients for C. leptoporus and C. pelagicus strains RCC1198 and RCC1200 are presented in Supporting Information Tables S1–S3, respectively.…”

“…Within a physiologically broad CO 2 /pH range, simulating OA, optimum curve responses for PIC and POC production, and growth rates have been observed in all coccolithophores so far (Langer et al ; Bach et al ; Sett et al ; Zhang et al ). Sensitivities of PIC, POC, and growth rates to OA vary as a result of differing substrate use (Kottmeier et al ), with those for PIC production being the most sensitive (Bach et al ; Gafar and Schulz ; N. A. Gafar et al ). As a result, OA influences the relative production of PIC and POC in coccolithophores.…”

“…Fit coefficients for G. oceanica, E. huxleyi, and S. apsteinii were taken from Gafar et al (2018b), Gafar and Schulz (2018), and N. A. Gafar et al (2019). Fit coefficients for C. leptoporus and C. pelagicus strains RCC1198 and RCC1200 are presented in Supporting Information Tables S1-S3, respectively.…”

“…Carbon production and growth rates of coccolithophores are significantly affected by environmental conditions (i.e., temperature, light, and CO 2 ; Langer et al 2006;Bach et al 2011;Sett et al 2014;Zhang et al 2015;N. A. Gafar et al 2019).…”

“…As a result, OA influences the relative production of PIC and POC in coccolithophores. Sensitivities to OA also vary between species with some such as G. oceanica being much more sensitive than others like E. huxleyi and S. apsteinii (Gafar et al 2018b;Gafar and Schulz 2018;N. A. Gafar et al 2019).…”