Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt;

Yuanyuan Feng,Philip W Boyd,Michael Y Roleda,Evelyn Armstrong,Catriona L Hurd,Cliff S Law

doi:10.5194/bg-15-581-2018

Abstract

Abstract. A series of semi-continuous incubation experiments were conducted with the coccolithophore Emiliania huxleyi strain NIWA1108 (Southern Ocean isolate) to examine the effects of five environmental drivers (nitrate and phosphate concentrations, irradiance, temperature, and partial pressure of CO2 (pCO2)) on both the physiological rates and elemental composition of the coccolithophore. Here, we report the alteration of the elemental composition of E. huxleyi in response to the changes in these environmental drivers. A series of dose–response curves for the cellular elemental composition of E. huxleyi were fitted for each of the five drivers across an environmentally representative gradient. The importance of each driver in regulating the elemental composition of E. huxleyi was ranked using a semi-quantitative approach. The percentage variations in elemental composition arising from the change in each driver between present-day and model-projected conditions for the year 2100 were calculated. Temperature was the most important driver controlling both cellular particulate organic and inorganic carbon content, whereas nutrient concentrations were the most important regulator of cellular particulate nitrogen and phosphorus of E. huxleyi. In contrast, elevated pCO2 had the greatest influence on cellular particulate inorganic carbon to organic carbon ratio, resulting in a decrease in the ratio. Our results indicate that the different environmental drivers play specific roles in regulating the elemental composition of E. huxleyi with wide-reaching implications for coccolithophore-related marine biogeochemical cycles, as a consequence of the regulation of E. huxleyi physiological processes.

Highlights

The global climate change induced by anthropogenic activities is causing a wide range of alterations to the marine environment including ocean acidification (OA), rising sea surface temperature (SST), and intensified stratification due to increased density gradients between surface and subsurface waters, with associated shifts in mean irradiance levels and nutrient availability in the upper water column (Boyd and Doney, 2002; Rost and Riebesell, 2004; Stocker, 2013)
It is the first to rank the importance of the predicted changes in these environmental drivers on E. huxleyi elemental stoichiometry for the year 2100 relative to the present-day conditions
Relating changes in elemental composition is an important addition to the responses of growth, photosynthesis, and calcification rates (Feng et al, 2017), providing insights into the biogeochemical consequences of the physiological effects induced by change in the five essential environmental drivers

Summary

Introduction

The global climate change induced by anthropogenic activities is causing a wide range of alterations to the marine environment including ocean acidification (OA), rising sea surface temperature (SST), and intensified stratification due to increased density gradients between surface and subsurface waters, with associated shifts in mean irradiance levels and nutrient availability in the upper water column (Boyd and Doney, 2002; Rost and Riebesell, 2004; Stocker, 2013) All these global changes in environmental variables will affect the physiology and ecology of phytoplankton, both individually and interactively, in a complex way (Boyd and Hutchins, 2012; Boyd et al, 2010, 2016; Feng et al, 2017). Such deviations subsequently influence the accumulation of these elements in the upper food web and marine biogeochemistry (Finkel et al, 2010; Ho et al, 2003; Sardans et al, 2012)

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