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Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores

Sheward, RM; Poulton, AJ; Gibbs, SJ; Daniels, CJ; Bown, PR; (2017) Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores. Biogeosciences , 14 (6) pp. 1493-1509. 10.5194/bg-14-1493-2017. Green open access

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Abstract

Coccolithophores are an abundant phytoplankton group that exhibit remarkable diversity in their biology, ecology and calcitic exoskeletons (coccospheres). Their extensive fossil record is a testament to their important biogeochemical role and is a valuable archive of biotic responses to environmental change stretching back over 200 million years. However, to realise the full potential of this archive for (palaeo-)biology and biogeochemistry requires an understanding of the physiological processes that underpin coccosphere architecture. Using culturing experiments on four modern coccolithophore species (Calcidiscus leptoporus, Calcidiscus quadriperforatus, Helicosphaera carteri and Coccolithus braarudii) from three long-lived families, we investigate how coccosphere architecture responds to shifts from exponential (rapid cell division) to stationary (slowed cell division) growth phases as cell physiology reacts to nutrient depletion. These experiments reveal statistical differences in coccosphere size and the number of coccoliths per cell between these two growth phases, specifically that cells in exponential-phase growth are typically smaller with fewer coccoliths, whereas cells experiencing growth-limiting nutrient depletion have larger coccosphere sizes and greater numbers of coccoliths per cell. Although the exact numbers are species-specific, these growth-phase shifts in coccosphere geometry demonstrate that the core physiological responses of cells to nutrient depletion result in increased coccosphere sizes and coccoliths per cell across four different coccolithophore families (Calcidiscaceae, Coccolithaceae, Isochrysidaceae and Helicosphaeraceae), a representative diversity of this phytoplankton group. Building on this, the direct comparison of coccosphere geometries in modern and fossil coccolithophores enables a proxy for growth phase to be developed that can be used to investigate growth responses to environmental change throughout their long evolutionary history. Our data also show that changes in growth rate and coccoliths per cell associated with growth-phase shifts can substantially alter cellular calcite production. Coccosphere geometry is therefore a valuable tool for accessing growth information in the fossil record, providing unprecedented insights into the response of species to environmental change and the potential biogeochemical consequences.

Type: Article
Title: Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores
Open access status: An open access version is available from UCL Discovery
DOI: 10.5194/bg-14-1493-2017
Publisher version: http://doi.org/10.5194/bg-14-1493-2017
Language: English
Additional information: © Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License.
Keywords: Science & Technology, Life Sciences & Biomedicine, Physical Sciences, Ecology, Geosciences, Multidisciplinary, Environmental Sciences & Ecology, Geology, EMILIANIA-HUXLEYI PRYMNESIOPHYCEAE, SEAWATER CARBONATE CHEMISTRY, CALCIDISCUS-LEPTOPORUS, OCEAN ACIDIFICATION, ENVIRONMENTAL CONTROLS, PELAGICUS HAPTOPHYTA, NUTRIENT LIMITATION, FOSSIL COCCOSPHERES, CRYPTIC SPECIATION, THERMAL MAXIMUM
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1550556
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