Growth of the coccolithophore &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; in light- and nutrient-limited batch reactors: relevance for the BIOSOPE deep ecological niche of coccolithophores

Laura Perrin,Ian Probert,Giovanni Aloisi,Gerald Langer

doi:10.5194/bg-13-5983-2016

Abstract

Abstract. Coccolithophores are unicellular calcifying marine algae that play an important role in the oceanic carbon cycle via their cellular processes of photosynthesis (a CO2 sink) and calcification (a CO2 source). In contrast to the well-studied, surface-water coccolithophore blooms visible from satellites, the lower photic zone is a poorly known but potentially important ecological niche for coccolithophores in terms of primary production and carbon export to the deep ocean. In this study, the physiological responses of an Emiliania huxleyi strain to conditions simulating the deep niche in the oligotrophic gyres along the BIOSOPE transect in the South Pacific Gyre were investigated. We carried out batch culture experiments with an E. huxleyi strain isolated from the BIOSOPE transect, reproducing the in situ conditions of light and nutrient (nitrate and phosphate) limitation. By simulating coccolithophore growth using an internal stores (Droop) model, we were able to constrain fundamental physiological parameters for this E. huxleyi strain. We show that simple batch experiments, in conjunction with physiological modelling, can provide reliable estimates of fundamental physiological parameters for E. huxleyi that are usually obtained experimentally in more time-consuming and costly chemostat experiments. The combination of culture experiments, physiological modelling and in situ data from the BIOSOPE cruise show that E. huxleyi growth in the deep BIOSOPE niche is limited by availability of light and nitrate. This study contributes more widely to the understanding of E. huxleyi physiology and behaviour in a low-light and oligotrophic environment of the ocean.

Highlights

Coccolithophores are unicellular, photosynthetic and calcifying algae that are very abundant in the marine environment and play key roles in the global carbon cycle (Paasche, 2002; Roth, 1994)
We show that batch cultures, if coupled to simple physiological modelling, may provide valuable estimates of fundamental physiological parameters that are more widely obtained in more time-consuming and costly chemostat experiments (Eppley and Renger, 1974; Terry, 1982; Riegman et al, 2000; Müller et al, 2012)
Experiments run in high-light conditions attained target cell densities or nutrient limitation in a shorter time compared to experiments run in low-light conditions

Summary

Introduction

Coccolithophores are unicellular, photosynthetic and calcifying algae that are very abundant in the marine environment and play key roles in the global carbon cycle (Paasche, 2002; Roth, 1994). Through photosynthesis they contribute to the upper ocean carbon pump (CO2 sink), while via calcification they contribute to the carbonate counter-pump (CO2 source) (Paasche, 2002; Westbroek et al, 1993). The relative importance of calcification and photosynthesis is one of the factors that dictates the effect of coccolithophores on ocean– atmosphere CO2 fluxes (Shutler et al, 2013).

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