Influence of CO2 and nitrogen limitation on the coccolith volume of Emiliania huxleyi (Haptophyta)
1Institute for Marine and Antarctic Studies (IMAS), Private Bag 129, Hobart, TAS 7001, Australia
2CNRS/Université Aix-Marseille, CEREGE, 13545 Aix-en-Provence, Cedex 4, France
3INRIA (French National Institute for Research in Computer Science and Automatic Control), BIOCORE, 2004 Route des Lucioles, 06902 Sophia-Antipolis, France
4UPMC Univ. Paris 06, UMR7093, LOV, Observatoire océanologique, 06234 Villefranche/mer, France
5CNRS, UMR7093, LOV, Observatoire océanologique, 06234 Villefranche/mer, France
Abstract. Coccolithophores, a key phytoplankton group, are one of the best studied organisms with regard to the response to ocean acidification/carbonation. The biogenic production of calcareous coccoliths has made coccolithophores a promising group for paleoceanographic research aiming to reconstruct past environmental conditions. Recently, geochemical and morphological analyses of fossil coccoliths have gained increased interest in regard to changes in seawater carbonate chemistry. The cosmopolitan coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler was cultured over a range of pCO2 levels in controlled laboratory experiments under nutrient replete and nitrogen limited conditions. Measurements of photosynthetic activity and calcification revealed, as previously published, an increase in organic carbon production and a moderate decrease in calcification from ambient to elevated pCO2. The enhancement in particulate organic carbon production was accompanied by an increase in cell diameter. Coccolith volume was best correlated with the coccosphere/cell diameter and no significant correlation was found between coccolith volume and particulate inorganic carbon production rate. The conducted experiments revealed that the coccolith volume of E. huxleyi is variable with aquatic CO2 concentration within the tested range but appears to be a primary function of the coccosphere/cell diameter both under nitrogen limited and nutrient replete conditions. Comparing coccolith morphological and geometrical parameters like volume, mass and size to physiological parameters under controlled laboratory conditions is an important step to understand variations in fossil coccolith geometry.