On culture artefacts in coccolith morphology
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ORIGINAL ARTICLE
On culture artefacts in coccolith morphology Gerald Langer • Kerstin Oetjen • Tina Brenneis
Received: 11 January 2012 / Revised: 31 July 2012 / Accepted: 9 August 2012 / Published online: 5 September 2012 Ó Springer-Verlag and AWI 2012
Abstract Coccolith malformations occur more frequently in cultured specimens than in specimens from natural samples, a phenomenon commonly termed ‘culture artefacts’. The causes of culture artefacts are unknown. Here, we tested the effect of culture flask shape, mixing, and cell density on the morphology of Emiliania huxleyi coccoliths. While there was no effect of different culture flask types typically used in coccolithophore culturing, continuous mixing reduced the percentage of malformations by ca. 11 % in exponential-phase cells (cell density ca. 80 9 103 cells per ml) and ca. 17 % in stationary-phase cells (cell density ca. 2 9 106 cells per ml). Stationary-phase cells displayed 19 % more malformations than mid-exponentialphase cells when not mixed at all and 20 % more malformations when continuously mixed. It is concluded that the lack of mixing and unnaturally high cell densities, typical for coccolithophore stock cultures, are partly responsible for culture artefacts. Keywords Emiliania huxleyi Coccolith morphology Culture artefacts
Communicated by H.-D. Franke. G. Langer (&) Department of Earth Sciences, Cambridge University, Downing St., Cambridge CB2 3EQ, UK e-mail: [email protected] K. Oetjen T. Brenneis Biogeosciences, Alfred Wegener Institute for Polar and Marine Research, 27570 Bremerhaven, Germany
Introduction Coccolithophores, unicellular haptophyte algae, surround themselves with a sphere consisting of coccoliths, elaborately crafted calcareous platelets. Coccolith-calcite is, besides foraminiferal calcite, the most important pelagic source of calcium carbonate (Baumann et al. 2004). The latter feature, amongst others, renders coccolithophore biology in general and coccolith production in particular a topic of broad interest. Over the last decade, the potential response of coccolithophores to ocean acidification (Royal Society 2005) has received special attention. Ocean acidification refers to the decrease in sea surface water pH caused by anthropogenic CO2 emissions and the subsequent uptake of CO2 by the oceans. In a seminal study, it was first put forth that coccolith malformations (for details, see below) increase with increasing CO2/decreasing pH in a particular culture strain of Emiliania huxleyi (Riebesell et al. 2000). The latter observation gave rise to the notion that coccolith malformations can be used as an indicator of ocean acidification. Subsequently, the applicability of laboratory observations to the coccolith sedimentary record was explored using a, with respect to morphology, particularly sensitive species (Langer et al. 2006). Recently, it was argued that coccolith malformations in response to ocean acidification are crucial to the question of how coccolithophores will perform in an acidifying ocean (Langer et al. 2011).
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