A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change

Coccolithophore responses to changes in carbonate chemistry speciation such as CO2 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 abundant coccolithophores in today’s oceans appear to be adapted for a similar fundamental light niche but slightly different ones for temperature and CO2, with E. huxleyi having a tolerance to lower temperatures and higher CO2 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 CO2 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 RCP 8.5 climate change scenario (1000 μatm fCO2 and +4.8 °C) we project a niche contraction for G. oceanica then being restricted to regions of even higher 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 CaCO3 production potential (CCPP). Excluding the Antarctic province from the analysis we found a good correlation between CCPP and satellite derived PIC in the other regions with an R2 of 0.73 for Austral winter/Boreal summer and 0.85 for Austral summer/Boreal winter.

Gafar N. A. & Schulz K. G., 2018.  A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change. Biogeosciences Discussions. doi:10.5194/bg-2018-88. Article

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