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

Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores
Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores
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.
1726-4170
1493-1509
Sheward, Rosie M.
21a9f84a-f0b2-4488-9ab9-1482ce26e18e
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Gibbs, Samantha J.
82dfbcbc-3a8a-40da-8a80-fe7ad83f3110
Daniels, Chris J.
aec2572b-e302-4f8e-ab7a-86b8bdf1c155
Bown, Paul R.
773e1a6d-1c12-4e57-af3b-ec981390a64a
Sheward, Rosie M.
21a9f84a-f0b2-4488-9ab9-1482ce26e18e
Poulton, Alex J.
14bf64a7-d617-4913-b882-e8495543e717
Gibbs, Samantha J.
82dfbcbc-3a8a-40da-8a80-fe7ad83f3110
Daniels, Chris J.
aec2572b-e302-4f8e-ab7a-86b8bdf1c155
Bown, Paul R.
773e1a6d-1c12-4e57-af3b-ec981390a64a

Sheward, Rosie M., Poulton, Alex J., Gibbs, Samantha J., Daniels, Chris J. and Bown, Paul R. (2017) Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores. Biogeosciences, 14 (6), 1493-1509. (doi:10.5194/bg-14-1493-2017).

Record type: Article

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.

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More information

Accepted/In Press date: 24 February 2017
e-pub ahead of print date: 24 March 2017
Organisations: Ocean and Earth Science, Ocean Biochemistry & Ecosystems, National Oceanography Centre, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 407673
URI: http://eprints.soton.ac.uk/id/eprint/407673
ISSN: 1726-4170
PURE UUID: 22489862-6c0d-48d9-99c7-ae96d8451ad9

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Date deposited: 22 Apr 2017 01:03
Last modified: 27 Apr 2022 12:18

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Contributors

Author: Rosie M. Sheward
Author: Alex J. Poulton
Author: Samantha J. Gibbs
Author: Chris J. Daniels
Author: Paul R. Bown

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