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Front. Mar. Sci. | doi: 10.3389/fmars.2018.00067

Reading the fine print: Ultra-microstructures of foraminiferal calcification revealed using focused ion beam microscopy

  • 1Graduate School of Environment and Information Sciences, Yokohama National University, Japan
  • 2Department of Biodivesity (B-DIVE), Japan Agency for Marine-Earth Science and Technology, Japan
  • 3Marine Works Japan LTD, Japan
  • 4Faculty of Environment and Information Sciences, Yokohama National University, Japan
  • 5Tokyo University of Marine Science and Technology, Japan

The elemental composition of calcite is of critical value in paleoceanographic reconstructions, yet little is known about biological processes underlying elemental uptake by foraminifers during calcification. Especially crucial in the understanding of elemental composition and distribution is the involvement of organic templates separating different layers of calcite forming the wall of a foraminiferal chamber. In this study, we applied the focused ion beam (FIB) scanning electron microscopy (SEM) technique to the site of calcification (SOC) in a newly growing chamber of Ammonia beccarii, a benthic foraminifer, to reveal the ultra- and microstructure during calcification. This allowed cross-sections of both soft and hard tissues, allowing detailed observation of the SOC across a series of calcification stages. For the first time, we show that numerous voids of calcareous layers and internal organic structures are present within the SOC during the calcification process. The series of SEM observations suggest that organic layers are actively involved in calcite precipitation. We provide the first evidence that the SOC is isolated from surrounding seawater during calcification. Our findings improve the understanding of foraminiferal biomineralization and characterize key conditions under which element partitioning and isotope fractionation occur.

Keywords: Foraminifera, Biomineralization, ultrastructure, calcification, FIB, SEM, Marine Biology, micropaleontology

Received: 25 Jul 2017; Accepted: 14 Feb 2018.

Edited by:

Andrew S. Mount, Clemson University, United States

Reviewed by:

Dennis A. Bazylinski, University of Nevada, Las Vegas, United States
Gary H. Dickinson, The College of New Jersey, United States  

Copyright: © 2018 Nagai, Uematsu, Wani and Toyofuku. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Takashi Toyofuku, Japan Agency for Marine-Earth Science and Technology, Department of Biodivesity (B-DIVE), Natsushima-cho 2-15, Yokosuka, 237-0061, Kanagawa, Japan, toyofuku@jamstec.go.jp