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

Gafar, Natasha A.; Schulz, Kai G.

Coccolithophore responses to changes in carbonate chemistry speciation such as inline-formulaCO2 and inline-formulaH+ 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 inline-formulaCO2, with E. huxleyi having a tolerance to lower temperatures and higher inline-formulaCO2 levels than G. oceanica. Based on growth rates, a dominance of E. huxleyi over G. oceanica is projected below temperatures of 22 inline-formulaC at current atmospheric inline-formulaCO2 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 inline-formulaµatm inline-formulafinline-formulaCO2), we project a inline-formulaCO2 driven niche contraction for G. oceanica to regions of even higher temperatures. However, the greater sensitivity of G. oceanica to increasing inline-formulaCO2 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 inline-formulaCaCO3 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 inline-formulaR2 of 0.73, inline-formulap < 0.01 and a slope of 1.03 for austral winter/boreal summer and an inline-formulaR2 of 0.85, inline-formulap < 0.01 and a slope of 0.32 for austral summer/boreal winter.



Gafar, Natasha A. / Schulz, Kai G.: A three-dimensional niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica: reconciling observations with projections. 2018. Copernicus Publications.


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