A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica : reconciling observations with projections

• Published in: Biogeosciences
• Main Authors: N. A. Gafar, K. G. Schulz
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Antarctic; Austral; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/bg-15-3541-2018; https://doaj.org/article/c6287408e2ed4e7c8f3920a45f2c3535

Coccolithophore responses to changes in carbonate chemistry speciation such as CO 2 and H + are highly modulated by light intensity and temperature. Here, we fit an analytical equation, accounting for simultaneous changes in carbonate chemistry speciation, light and temperature, to published and original data for Emiliania huxleyi , and compare the projections with those for Gephyrocapsa oceanica . Based on our analysis, the two most common bloom-forming species in present-day coccolithophore communities appear to be adapted for a similar fundamental light niche but slightly different ones for temperature and CO 2 , with E. huxleyi having a tolerance to lower temperatures and higher CO 2 levels than G. oceanica . Based on growth rates, a dominance of E. huxleyi over G. oceanica is projected below temperatures of 22 °C at current atmospheric CO 2 levels. This is similar to a global surface sediment compilation of E. huxleyi and G. oceanica coccolith abundances suggesting temperature-dependent dominance shifts. For a future Representative Concentration Pathway (RCP) 8.5 climate change scenario (1000 µatm f CO 2 ), we project a CO 2 driven niche contraction for G. oceanica to regions of even higher temperatures. However, the greater sensitivity of G. oceanica to increasing CO 2 is partially mitigated by increasing temperatures. Finally, we compare satellite-derived particulate inorganic carbon estimates in the surface ocean with a recently proposed metric for potential coccolithophore success on the community level, i.e. the temperature-, light- and carbonate-chemistry-dependent CaCO 3 production potential (CCPP). Based on E. huxleyi alone, as there was interestingly a better correlation than when in combination with G. oceanica , and excluding the Antarctic province from the analysis, we found a good correlation between CCPP and satellite-derived particulate inorganic carbon (PIC) with an R 2 of 0.73, p < 0.01 and a slope of 1.03 for austral winter/boreal summer and an R 2 of 0.85, p < 0.01 and a slope of ...