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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 21
Biogeosciences, 15, 6607-6619, 2018
https://doi.org/10.5194/bg-15-6607-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 6607-6619, 2018
https://doi.org/10.5194/bg-15-6607-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Nov 2018

Research article | 07 Nov 2018

Factors influencing test porosity in planktonic foraminifera

Janet E. Burke1, Willem Renema2, Michael J. Henehan1,3, Leanne E. Elder1, Catherine V. Davis4, Amy E. Maas5, Gavin L. Foster6, Ralf Schiebel7, and Pincelli M. Hull1 Janet E. Burke et al.
  • 1Department of Geology and Geophysics, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA
  • 2Naturalis Biodiversity Center, P.O. Box 91517, 2300 RA Leiden, the Netherlands
  • 3GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
  • 4School of the Earth, Ocean, and Environment, University of South Carolina, 701 Sumter Street, EWS 617, Columbia, SC 29208, USA
  • 5Bermuda Institute of Ocean Sciences, 17 Biological Station, Ferry Reach, St. George's GE 01, Bermuda
  • 6Ocean and Earth Science, University of Southampton, National Oceanography Centre, University Road, Southampton, SO17 1BJ, UK
  • 7Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany

Abstract. The clustering of mitochondria near pores in the test walls of foraminifera suggests that these perforations play a critical role in metabolic gas exchange. As such, pore measurements could provide a novel means of tracking changes in metabolic rate in the fossil record. However, in planktonic foraminifera, variation in average pore area, density, and porosity (the total percentage of a test wall that is open pore space) have been variously attributed to environmental, biological, and taxonomic drivers, complicating such an interpretation. Here we examine the environmental, biological, and evolutionary determinants of pore characteristics in 718 individuals, representing 17 morphospecies of planktonic foraminifera from 6 core tops in the North Atlantic. Using random forest models, we find that porosity is primarily correlated to test surface area, test volume, and habitat temperature, key factors in determining metabolic rates. In order to test if this correlation arose spuriously through the association of cryptic species with distinct biomes, we cultured Globigerinoides ruber in three different temperature conditions, and found that porosity increased with temperature. Crucially, these results show that porosity can be plastic: changing in response to environmental drivers within the lifetime of an individual foraminifer. This demonstrates the potential of porosity as a proxy for foraminiferal metabolic rates, with significance for interpreting geochemical data and the physiology of foraminifera in non-analog environments. It also highlights the importance of phenotypic plasticity (i.e., ecophenotypy) in accounting for some aspects of morphological variation in the modern and fossil record.

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Metabolic rates are sensitive to environmental conditions and can skew geochemical measurements. However, there is no way to track these rates through time. Here we investigate the controls of test porosity in planktonic foraminifera (organisms commonly used in paleoclimate studies) as a potential proxy for metabolic rate. We found that the porosity varies with body size and temperature, two key controls on metabolic rate, and that it can respond to rapid changes in ambient temperature.
Metabolic rates are sensitive to environmental conditions and can skew geochemical measurements....
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